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  • 1.
    Abegunawardana, Sidath
    et al.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Bodhika, J A P
    Univ Ruhuna, Dept Phys, Matara, Sri Lanka.
    Abewardhana, Ruwan
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Fernando, Mahendra
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Sound Source Localization of Lightning Discharges2018Conference paper (Refereed)
    Abstract [en]

    The lightning channel can be retraced by thunder signature recorded with an array of microphones. Four microphones were arranged to capture thunder sound, and acoustic cross-correlation of captured pressure signals estimated the time lag of each pair of microphones. A wave segment with 0.25 s or 0.5 s of duration was compared with the acoustic signal recorded by other microphones to estimate time lapse. The direction of channel propagation has been estimated by the time difference of arrival of each pair of microphones. Thunder source locations estimated by this method can be extended to investigate the channel propagation inside clouds.

  • 2.
    Abegunawardana, Sidath
    et al.
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Bodhika, J A P
    Univ Ruhuna, Dept Phys, Matara, Sri Lanka.
    Nanayakkara, Sankha
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Sonnadara, Upul
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Fernando, Mahendra
    Univ Colombo, Dept Phys, Colombo, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Audible Frequency Analysis of Ground Flashes2018Conference paper (Refereed)
    Abstract [en]

    Thunder signatures categorized into three types based on peak pressure and variation in fundamental frequency, have been studied by using acoustic spectrum of thunder. S-transformation has been used to estimate the dominant frequency variation around the peak pressure. The mean fundamental frequencies of type 3 ground and cloud flashes are 160 Hz and 98 Hz respectively. The mean frequencies of type 2 ground and cloud flashes are 108 Hz and 82 Hz respectively.

  • 3.
    Agnihotri, Sagar Narhari
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Liu, Zhenhua
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Barbe, Laurent
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Fornell, Anna
    Tenje, Maria
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering. Uppsala University, Science for Life Laboratory, SciLifeLab.
    Droplet Acoustofluidics and Pico-injection for Long-term Cell Culture2022Conference paper (Other academic)
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  • 4.
    Aihara, Aya
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Aeroacoustic Prediction for Vertical Axis Wind Turbines2021Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis investigates the aerodynamic and aeroacoustic prediction of vertical axis wind turbines, using computational fluid dynamics simulations. Noise pollution from wind turbines is one of the disadvantages of wind energy, calling for strategies to reduce noise levels. Yet for vertical axis wind turbines in particular, there is insufficient knowledge of how to identify sound sources and mitigate the sound level. The aim of this study is to predict aerodynamic noise, using large eddy simulation and acoustic analogy, so as to better understand the mechanism of sound generation for vertical axis wind turbines. First, the prediction method is validated for a static single blade in stall. This model is able to capture the dominant frequency, but it does not well reproduce the broadband characteristics. Next, the aerodynamic behavior of the 12 kW H-rotor vertical axis wind turbine is studied, whereby the focus is on the importance of properly modeling the strut influence for an accurate prediction of the blade forces. To achieve this, the flow field is solved for three different tip speed ratios. The results show that the struts significantly affect on the force distribution along the blade. The reduction of the blade force is observed to occur not only at the attachment points of the struts, but also over a large area of the blade section in the downwind side where the blade interacts with the wake created in the upwind. Finally, the noise radiated from the vertical axis wind turbine operating at high tip speed ratio is predicted. Measurements are conducted to validate the prediction, with the experimental data representing the broadband noise characteristics dominant at around 800 Hz. The prediction reproduces the sound pressure level observed at a radial distance of 1.4 rotor diameter, with a few decibels difference. However, these discrepancies become more pronounced at double distance, which can be considered to arise due to the effect of the ground reflection being ignored. The simulation furthermore indicates, that the main sound sources are emitted when the blade rotates in the downwind. It is suggested that future work should properly consider the atmospheric turbulence for more accurate predictions.

    List of papers
    1. LES prediction for acoustic noise of airfoil at high angle of attack
    Open this publication in new window or tab >>LES prediction for acoustic noise of airfoil at high angle of attack
    2020 (English)Conference paper, Oral presentation with published abstract (Refereed)
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-426027 (URN)10.2514/6.2020-1723 (DOI)
    Conference
    AIAA Scitech 2020 Forum
    Available from: 2020-11-23 Created: 2020-11-23 Last updated: 2021-12-28
    2. Numerical prediction of noise generated from airfoil in stall using LES and acoustic analogy
    Open this publication in new window or tab >>Numerical prediction of noise generated from airfoil in stall using LES and acoustic analogy
    2021 (English)In: Noise & Vibration Worldwide, ISSN 0957-4565, E-ISSN 2048-4062, Vol. 52, no 10, p. 295-305Article in journal (Other academic) Published
    Abstract [en]

    This article presents the aerodynamic noise prediction of a NACA 0012 airfoil in stall region using Large Eddy Simulation and the acoustic analogy. While most numerical studies focus on noise for an airfoil at a low angle of attack, prediction of stalled noise has been made less sufficiently. In this study, the noise of a stalled airfoil is calculated using the spanwise correction where the total noise is estimated from the sound source of the simulated span section based on the coherence of turbulent flow structure. It is studied for the airfoil at the chord-based Reynolds number of 4.8 × 105 and the Mach number of 0.2 with the angle of attack of 15.6° where the airfoil is expected to be under stall condition. An incompressible flow is resolved to simulate the sound source region, and Curle’s acoustic analogy is used to solve the sound propagation. The predicted spectrum of the sound pressure level observed at 1.2 m from the trailing edge of the airfoil is validated by comparing measurement data, and the results show that the simulation is able to capture the dominant frequency of the tonal peak. However, while the measured spectrum is more broadband, the predicted spectrum has the tonal character around the primary frequency. This difference can be considered to arise due to insufficient mesh resolution.

    Place, publisher, year, edition, pages
    Sage Publications, 2021
    Keywords
    Acoustics, noise; airfoil, computational fluid dynamics, LES, Curle’s acoustic analogy
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-426035 (URN)10.1177/09574565211030706 (DOI)
    Available from: 2020-11-23 Created: 2020-11-23 Last updated: 2023-03-13Bibliographically approved
    3. A numerical study of strut influence on blade forces of vertical axis wind turbine using computational fluid dynamics simulation
    Open this publication in new window or tab >>A numerical study of strut influence on blade forces of vertical axis wind turbine using computational fluid dynamics simulation
    (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824Article in journal (Other academic) Submitted
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-426033 (URN)
    Available from: 2020-11-23 Created: 2020-11-23 Last updated: 2020-12-07
    4. Comparison of three-dimensional numerical methods for modeling of strut effect on aerodynamic forces of a vertical axis wind turbine
    Open this publication in new window or tab >>Comparison of three-dimensional numerical methods for modeling of strut effect on aerodynamic forces of a vertical axis wind turbine
    (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824Article in journal (Other academic) Submitted
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-426034 (URN)
    Available from: 2020-11-23 Created: 2020-11-23 Last updated: 2020-12-07
    5. Aeroacoustic noise prediction of a vertical axis wind turbine using Large Eddy Simulation
    Open this publication in new window or tab >>Aeroacoustic noise prediction of a vertical axis wind turbine using Large Eddy Simulation
    2021 (English)In: International Journal of Aeroacoustics, ISSN 1475-472X, E-ISSN 2048-4003, Vol. 20, no 8, p. 959-978Article in journal (Other academic) Published
    Abstract [en]

    This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

    Place, publisher, year, edition, pages
    Sage PublicationsSAGE Publications, 2021
    Keywords
    Vertical axis wind turbine, acoustics, aerodynamic noise, CFD, LES
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-426037 (URN)10.1177/1475472X211055179 (DOI)000721550900001 ()
    Funder
    Swedish National Infrastructure for Computing (SNIC)Swedish Research Council, 2020/5-321
    Available from: 2020-11-23 Created: 2020-11-23 Last updated: 2024-01-15Bibliographically approved
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  • 5.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    LES prediction for acoustic noise of airfoil at high angle of attack2020Conference paper (Refereed)
  • 6.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Numerical prediction of noise generated from airfoil in stall using LES and acoustic analogy2021In: Noise & Vibration Worldwide, ISSN 0957-4565, E-ISSN 2048-4062, Vol. 52, no 10, p. 295-305Article in journal (Other academic)
    Abstract [en]

    This article presents the aerodynamic noise prediction of a NACA 0012 airfoil in stall region using Large Eddy Simulation and the acoustic analogy. While most numerical studies focus on noise for an airfoil at a low angle of attack, prediction of stalled noise has been made less sufficiently. In this study, the noise of a stalled airfoil is calculated using the spanwise correction where the total noise is estimated from the sound source of the simulated span section based on the coherence of turbulent flow structure. It is studied for the airfoil at the chord-based Reynolds number of 4.8 × 105 and the Mach number of 0.2 with the angle of attack of 15.6° where the airfoil is expected to be under stall condition. An incompressible flow is resolved to simulate the sound source region, and Curle’s acoustic analogy is used to solve the sound propagation. The predicted spectrum of the sound pressure level observed at 1.2 m from the trailing edge of the airfoil is validated by comparing measurement data, and the results show that the simulation is able to capture the dominant frequency of the tonal peak. However, while the measured spectrum is more broadband, the predicted spectrum has the tonal character around the primary frequency. This difference can be considered to arise due to insufficient mesh resolution.

    Download full text (pdf)
    fulltext
  • 7.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Karl, Bolin
    The Marcus Wallenberg Laboratory, Department of Engineering Mechanics, KTH, Sweden.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Aeroacoustic noise prediction of a vertical axis wind turbine using Large Eddy Simulation2021In: International Journal of Aeroacoustics, ISSN 1475-472X, E-ISSN 2048-4003, Vol. 20, no 8, p. 959-978Article in journal (Other academic)
    Abstract [en]

    This study investigates the numerical prediction for the aerodynamic noise of the vertical axis wind turbine using large eddy simulation and the acoustic analogy. Low noise designs are required especially in residential areas, and sound level generated by the wind turbine is therefore important to estimate. In this paper, the incompressible flow field around the 12 kW straight-bladed vertical axis wind turbine with the rotor diameter of 6.5 m is solved, and the sound propagation is calculated based on the Ffowcs Williams and Hawkings acoustic analogy. The sound pressure for the turbine operating at high tip speed ratio is predicted, and it is validated by comparing with measurement. The measured spectra of the sound pressure observed at several azimuth angles show the broadband characteristics, and the prediction is able to reproduce the shape of these spectra. While previous works studying small-scaled vertical axis wind turbines found that the thickness noise is the dominant sound source, the loading noise can be considered to be a main contribution to the total sound for this turbine. The simulation also indicates that the received noise level is higher when the blade moves in the downwind than in the upwind side.

    Download full text (pdf)
    fulltext
  • 8.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Uppsala Univ, Dept Elect Engn, Div Elect, Uppsala, Sweden..
    Mendoza, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Hexicon, Slupskjulsvagen 30, S-11149 Stockholm, Sweden..
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    A numerical study of strut and tower influence on the performance of vertical axis wind turbines using computational fluid dynamics simulation2022In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 25, no 5, p. 897-913Article in journal (Refereed)
    Abstract [en]

    This paper presents the influence of the strut and the tower on the aerodynamic force of the blade for the vertical axis wind turbine (VAWT). It has been known that struts degrade the performance of VAWTs due to the inherent drag losses. In this study, three-dimensional Reynolds-averaged Navier-Stokes simulations have been conducted to investigate the effect of the strut and the tower on the flow pattern around the rotor region, the blade force distribution, and the rotor performance. A comparison has been made for three different cases where only the blade; both the blade and the strut; and all of the blade, the strut, and the tower are considered. A 12-kW three-bladed H-rotor VAWT has been studied for tip speed ratio of 4.16. This ratio is relatively high for this turbine, so the influence of the strut is expected to be crucial. The numerical model has been validated first for a single pitching blade and full VAWTs. The simulations show distinguished differences in the force distribution along the blade between two cases with and without struts. Since the wake from the struts interacts with the blades, the tangential force is reduced especially in the downwind side when the struts are considered. The calculated power coefficient is decreased by 43 %, which shows the importance of modeling the strut effect properly for accurate prediction of the turbine performance. The simulations also indicate that including the tower does not yield significant difference in the force distribution and the rotor power.

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  • 9.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering.
    Mendoza, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    A numerical study of strut influence on blade forces of vertical axis wind turbine using computational fluid dynamics simulationIn: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824Article in journal (Other academic)
  • 10.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Mendoza, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Hexicon AB, Ostra Jarnvagsgatan 27, S-11120 Stockholm, Sweden..
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Comparison of Three-Dimensional Numerical Methods for Modeling of Strut Effect on the Performance of a Vertical Axis Wind Turbine2022In: Energies, E-ISSN 1996-1073, Vol. 15, no 7, article id 2361Article in journal (Refereed)
    Abstract [en]

    This paper compares three different numerical models to evaluate their accuracy for predicting the performance of an H-rotor vertical-axis wind turbine (VAWT) considering the influence of struts. The strut of VAWTs is one factor that makes the flow feature around the turbine more complex and thus influences the rotor performance. The focus of this study is placed on analyzing how accurately three different numerical approaches are able to reproduce the force distribution and the resulting power, taking the strut effect into account. For the 12 kW straight-bladed VAWT, the blade force is simulated at three tip speed ratios by the full computational fluid dynamics (CFD) model based on the Reynolds-averaged Navier-Stokes (RANS) equations, the actuator line model (ALM), and the vortex model. The results show that all the models do not indicate a significant influence of the struts in the total force over one revolution at low tip speed ratio. However, at middle and high tip speed ratio, the RANS model reproduces the significant decrease of the total tangential force that is caused due to the strut. Additionally, the RANS and vortex models present a clear influence of the struts in the force distribution along the blade at all three tip speed ratios investigated. The prediction by the ALM does not show such distinctive features of the strut impact. The RANS model is superior to the other two models for predicting the power coefficient considering the strut effect, especially at high tip speed ratio.

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  • 11. Aihara, Aya
    et al.
    Mendoza, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Comparison of three-dimensional numerical methods for modeling of strut effect on aerodynamic forces of a vertical axis wind turbineIn: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824Article in journal (Other academic)
  • 12.
    Aihara, Aya
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Uzunoğlu, Bahri
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Florida State Univ, Dept Math, Tallahassee, FL, USA.
    Vortex induced vibration energy extraction modeling via forced versus free vibration2017In: Proceedings Of Oceans 2017 - Aberdeen, IEEE, 2017Conference paper (Refereed)
    Abstract [en]

    Vortex induced vibrations (VIV) for energy extraction have been revisited in last years by both marine power and wind power communities. Even though vortex induced vibrations have been focus of research for many years, energy extraction from vortex induced vibrations is relevantly new field which needs more detailed investigation and modeling. To this end, there has been recent experimental and modeling parametric studies where VIV was modeled by solution of one-degree-of-freedom ordinary differential equation spring system where engineering modeling of vortex induced vibration for energy extraction has been investigated based on a spring system with the forces defined from forced oscillation experiments where full coupling of free oscillations were not taken into account. Herein a Computational Fluid Dynamics (CFD) modeling of a circular cylinder will be studied to compare forced and free vibrations in the context of vortex-induced energy extraction. The model is essentially solved by partial differential isothermal incompressible Navier-Stokes equations to model fully mathematical model of the fluid-structure interaction of vortex induced vibration. The comparison between forced and free oscillation response studies of this paper will serve to improve the scientific knowledge where vortex induced vibration modeling are comparatively more limited. The preliminary results are presented herein for forced and free oscillations for the Reynolds number regimes Re = 100 and Re = 3800 in two dimensions for combinations of amplitudes and frequency of oscillations in the context of energy extraction modeling.

  • 13.
    Arnqvist, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Olivares-Espinosa, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Investigation of Turbulence Accuracy When Modeling Wind in Realistic Forests Using LES2019In: Progress In Turbulence Viii / [ed] Orlu, R Talamelli, A Peinke, J Oberlack, M, SPRINGER INTERNATIONAL PUBLISHING AG , 2019, p. 291-296Conference paper (Refereed)
    Abstract [en]

    This study presents an evaluation of wind field simulations, in neutral atmospheric conditions, above a heterogeneous forest. The calculations were performed with Large-Eddy Simulation (LES) code OpenFOAM, with explicit modelling of the forest through drag coefficient and forest density. The findings indicate that a large modelling domain is needed in order to reproduce the measurements in different wind directions, since the effect of far upwind forest characteristics influence the wind and turbulence profiles. It is further shown that even though the low resolution of the LES simulations lead to slightly misrepresented single point turbulence characteristics, two point turbulence characteristics are well predicted due to spatial filtering of the small scales.

  • 14.
    Asalya, Oday
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Nanotechnology and Functional Materials.
    Fjällborg, Joar
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Nanotechnology and Functional Materials.
    Effects of surface roughness on spillway flow behaviors2023Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This thesis examines the impact of spillway surface roughness on discharge capacity determination in hydraulic models. The study combines physical hydraulic modeling in a laboratory with Computational Fluid Dynamics (CFD) modeling using Fluent. The aim is to evaluate the effect of material roughness on spillway discharge determination for prototype spillways and outlets. The project includes a literature review, data collection, 3D modeling, model setup, numerical modeling, result analysis, comparison with other reports, and report writing. The results concluded that varying roughness heights as well as changing turbulence model and mesh settings did not significantly impact the final discharge (kg/s) at steady state. P-values less than 1e-7 for the average discharge at flowtime of [150 − tfinal[s]] suggests strong confidence in the statistical insignificance of varying roughness height affecting the discharge.

     

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  • 15.
    Asmuth, Henrik
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Efficient Large-­eddy Simulation for Wind Energy Applications2022Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Modelling the interaction of wind turbines with the ambient flow is essential for almost all technical aspects of wind energy exploitation. Large-eddy simulation (LES) is the most detailed approach feasible to model this complex interaction of wind turbines with the atmospheric boundary layer and the wakes of upstream turbines. Despite more than twenty years of fundamental research on wind turbine modelling with LES, applications of the method remain limited to academic use cases to date. The main bottleneck hindering a broader adoption of LES in the industrial practice is the large computational demand of the method. Nevertheless, it holds enormous potential for addressing various modelling challenges arising from current trends in wind energy.

    A promising alternative to classical numerical approaches for LES is the lattice Boltzmann method (LBM). In particular, GPU-based (graphics processing unit) implementations of the method provide significant performance gains and have enabled unprecedented computational efficiencies for LES in different fields of fluid dynamics. Still, the LBM´s potential for wind energy applications remains untapped due to open questions, some of which are specific to the field. This thesis addresses two specific problems in applications of LES to wind turbine and farm simulations. First, is the representation of wind turbines with the actuator line technique. And, second, is the modelling of the surface shear stress in simulations of atmospheric boundary layers. Both aspects are crucial to enable LES for wind energy applications with the LBM, as is usually done with conventional approaches.

    As for the former, an LBM implementation of the actuator line model is applied in multiple studies on wind turbine wakes. Code-to-code comparisons and experimental validations show that the model can accurately capture the aerodynamic forces acting on the turbine blades as well as the wake characteristics. For the simulation of boundary layer flows a novel LBM-specific wall model is developed. The model, referred to as inverse momentum exchange method, imposes the surface shear stress at the first offwall grid points by adjusting the slip velocity in bounce-back boundary schemes. Simulations are compared to theoretical, numerical, and experimental reference data of isothermal boundary layer flows. It is consistently found that both mean quantities and higherorder turbulence statistics can be well-captured by wall-modelled lattice Boltzmann LES using the presented wall model and the employed cumulant collision scheme.

    The results presented illustrate that the LBM is a suitable approach for state-of-the-art LES of wind turbine wakes and boundary layer flows. Moreover, the applied method is shown to be robust, and, above all, extremely computationally efficient. Based on the observed computational efficiencies, it is concluded that industry LES for wind energy applications is possible with GPU-based LBM solvers. Furthermore, additional studies presented in this thesis illustrate further potentials of the method. Such are applications of reinforcement learning to wind farm control or large-scale data generation for the training of deep learning models for wake predictions.

    List of papers
    1. The Actuator Line Model in Lattice Boltzmann Frameworks: Numerical Sensitivity and Computational Performance
    Open this publication in new window or tab >>The Actuator Line Model in Lattice Boltzmann Frameworks: Numerical Sensitivity and Computational Performance
    2019 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1256, article id 012022Article in journal (Refereed) Published
    Abstract [en]

    The growing use of large-eddy simulations for the modelling of wind farms makes the need for efficient numerical frameworks more essential than ever. GPU-accelerated implementations of the Lattice Boltzmann Method (LBM) have shown to provide significant performance gains over classical Navier-Stokes-based computational fluid dynamics. Yet, their use in the field of wind energy remains limited to date. In this fundamental study the cumulant LBM is scrutinised for actuator line simulations of wind turbines. The numerical sensitivity of the method in a simple uniform inflow is investigated with respect to spatial and temporal resolution as well as the width of the actuator line’s regularisation kernel. Comparable accuracy and slightly better stability properties are shown in relation to a standard Navier-Stokes implementation. The results indicate the overall suitability of the cumulant LBM for wind turbine wake simulations. The potential of the LBM for future wind energy applications is clarified by means of a brief comparison of computational performance.

    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-411385 (URN)10.1088/1742-6596/1256/1/012022 (DOI)000560954100022 ()
    Conference
    Wake Conference 2019, 22–24 May 2019, Visby, Sweden
    Funder
    Swedish National Infrastructure for Computing (SNIC)
    Available from: 2020-06-01 Created: 2020-06-01 Last updated: 2022-02-28Bibliographically approved
    2. Actuator line simulations of wind turbine wakes using the lattice Boltzmann method
    Open this publication in new window or tab >>Actuator line simulations of wind turbine wakes using the lattice Boltzmann method
    2020 (English)In: Wind Energy Science, ISSN 2366-7443, E-ISSN 2366-7451, Vol. 5, no 2, p. 623-645Article in journal (Refereed) Published
    Abstract [en]

    The high computational demand of large-eddy simulations (LESs) remains the biggest obstacle for a wider applicability of the method in the field of wind energy. Recent progress of GPU-based (graphics processing unit) lattice Boltzmann frameworks provides significant performance gains alleviating such constraints. The presented work investigates the potential of LES of wind turbine wakes using the cumulant lattice Boltzmann method (CLBM). The wind turbine is represented by the actuator line model (ALM). The implementation is validated and discussed by means of a code-to-code comparison to an established finite-volume Navier–Stokes solver. To this end, the ALM is subjected to both laminar and turbulent inflow while a standard Smagorinsky sub-grid-scale model is employed in the two numerical approaches. The resulting wake characteristics are discussed in terms of the first- and second-order statistics as well the spectra of the turbulence kinetic energy. The near-wake characteristics in laminar inflow are shown to match closely with differences of less than 3 % in the wake deficit. Larger discrepancies are found in the far wake and relate to differences in the point of the laminar-turbulent transition of the wake. In line with other studies, these differences can be attributed to the different orders of accuracy of the two methods. Consistently better agreement is found in turbulent inflow due to the lower impact of the numerical scheme on the wake transition. In summary, the study outlines the feasibility of wind turbine simulations using the CLBM and further validates the presented set-up. Furthermore, it highlights the computational potential of GPU-based LBM implementations for wind energy applications. For the presented cases, near-real-time performance was achieved using a single, off-the-shelf GPU on a local workstation.

    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-411386 (URN)10.5194/wes-5-623-2020 (DOI)000537585500003 ()
    Funder
    Swedish National Infrastructure for Computing (SNIC)
    Available from: 2020-06-01 Created: 2020-06-01 Last updated: 2022-02-28Bibliographically approved
    3. Assessment of Weak Compressibility in Actuator Line Simulations of Wind Turbine Wakes
    Open this publication in new window or tab >>Assessment of Weak Compressibility in Actuator Line Simulations of Wind Turbine Wakes
    Show others...
    2020 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1618, article id 062057Article in journal (Refereed) Published
    Abstract [en]

    The trend of increasing rotor diameters and tip-speeds has brought about concerns of non-negligible compressibility effects in wind turbine aerodynamics. The investigation of such effects on wakes is particularly difficult when using actuator line models (ALM). This is because crucial regions of the flow, i.e. the direct vicinity of the blade, are not simulated but represented by body forces. To separately assess the impact of compressibility on the wake and the ALM itself, we conduct large-eddy simulations (LES) where the forces of the ALM are prescribed and based on the local sampled velocity (standard procedure), respectively. The LES are based on the weakly-compressible Lattice Boltzmann Method (LBM). Further to the comparison of (near-)incompressible to compressible simulations we investigate cases with artificially increased compressibility. This is commonly done in weakly-compressible approaches to reduce the computational demand. The investigation with prescribed forces shows that compressibility effects in the wake flow are negligible. Small differences in the wake velocity (of max. 1%) are found to be related to local compressibility effects in the direct vicinity of the ALM. Most significantly, compressibility is found to affect the sampled velocity and thereby accuracy of the ALM.

    Place, publisher, year, edition, pages
    IOP Publishing, 2020
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-411388 (URN)10.1088/1742-6596/1618/6/062057 (DOI)000686550403047 ()
    Conference
    Science of making torque from wind (TORQUE 2020), Delft Univ Technol, Online, Sep 28- Oct 02, 2020
    Available from: 2020-06-01 Created: 2020-06-01 Last updated: 2022-02-28Bibliographically approved
    4. Exploring the application of reinforcement learning to wind farm control
    Open this publication in new window or tab >>Exploring the application of reinforcement learning to wind farm control
    2021 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1934, article id 012022Article in journal (Refereed) Published
    Abstract [en]

    Optimal control of wind farms to maximize power is a challenging task since the wake interaction between the turbines is a highly nonlinear phenomenon. In recent years the field of Reinforcement Learning has made great contributions to nonlinear control problems and has been successfully applied to control and optimization in 2D laminar flows. In this work, Reinforcement Learning is applied to wind farm control for the first time to the authors' best knowledge. To demonstrate the optimization abilities of the newly developed framework, parameters of an already existing control strategy, the helix approach, are tuned to optimize the total power production of a small wind farm. This also includes an extension of the helix approach to multiple turbines. Furthermore, it is attempted to develop novel control strategies based on the control of the generator torque. The results are analysed and difficulties in the setup in regards to Reinforcement Learning are discussed. The tuned helix approach yields a total power increase of 6.8 % on average for the investigated case, while the generator torque controller does not yield an increase in total power. Finally, an alternative setup is proposed to improve the design of the problem.

    Place, publisher, year, edition, pages
    Institute of Physics Publishing (IOPP)IOP Publishing, 2021
    National Category
    Energy Engineering Control Engineering
    Identifiers
    urn:nbn:se:uu:diva-459807 (URN)10.1088/1742-6596/1934/1/012022 (DOI)000712011500022 ()
    Conference
    Wake Conference, JUN 15-17, 2021, ELECTR NETWORK
    Available from: 2021-11-29 Created: 2021-11-29 Last updated: 2024-01-15Bibliographically approved
    5. Wall-modeled lattice Boltzmann large-eddy simulation of neutral atmospheric boundary layers
    Open this publication in new window or tab >>Wall-modeled lattice Boltzmann large-eddy simulation of neutral atmospheric boundary layers
    2021 (English)In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 33, no 10, p. 105111-105111Article in journal (Refereed) Published
    Abstract [en]

    The lattice Boltzmann method (LBM) sees a growing popularity in the field of atmospheric sciences and wind energy, largely due to itsexcellent computational performance. Still, LBM large-eddy simulation (LES) studies of canonical atmospheric boundary layer flows remainlimited. One reason for this is the early stage of development of LBM-specific wall models. In this work, we discuss LBM–LES of isothermalpressure-driven rough-wall boundary layers using a cumulant collision model. To that end, we also present a novel wall modeling approach,referred to as inverse momentum exchange method (iMEM). The iMEM enforces a wall shear stress at the off-wall grid points by adjustingthe slip velocity in bounce-back boundary schemes. In contrast to other methods, the approach does not rely on the eddy viscosity, nor doesit require the reconstruction of distribution functions. Initially, we investigate different aspects of the modeling of the wall shear stress, i.e.,an averaging of the input velocity as well as the wall-normal distance of its sampling location. Particularly, sampling locations above the firstoff-wall node are found to be an effective measure to reduce the occurring log-layer mismatch. Furthermore, we analyze the turbulence statis-tics at different grid resolutions. The results are compared to phenomenological scaling laws, experimental, and numerical references. Theanalysis demonstrates a satisfactory performance of the numerical model, specifically when compared to a well-established mixed pseudo-spectral finite difference (PSFD) solver. Generally, the study underlines the suitability of the LBM and particularly the cumulant LBM forcomputationally efficient LES of wall-modeled boundary layer flows.

    Place, publisher, year, edition, pages
    American Institute of Physics (AIP)AIP Publishing, 2021
    National Category
    Fluid Mechanics and Acoustics
    Research subject
    Meteorology
    Identifiers
    urn:nbn:se:uu:diva-468298 (URN)10.1063/5.0065701 (DOI)000756198200038 ()
    Available from: 2022-02-23 Created: 2022-02-23 Last updated: 2024-01-15Bibliographically approved
    6. Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements
    Open this publication in new window or tab >>Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements
    Show others...
    2022 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 191, p. 868-887Article in journal (Refereed) Published
    Abstract [en]

    Predicting the power and loads of wind turbines in waked inflow conditions still presents a major modelling challenge. It requires the accurate modelling of the atmospheric flow conditions, wakes of upstream turbines and the response of the turbine of interest. Rigorous validations of model frameworks against measurements of utility-scale wind turbines in such scenarios remain limited to date. In this study, six models of different fidelity are compared against measurements from the DanAero experiment. The two benchmark cases feature a full-wake and partial-wake scenario, respectively. The simulations are compared against local pressure forces and inflow velocities measured on several blade sections of the downstream turbine, as well as met mast measurements and standard SCADA data. Regardless of the model fidelity, reasonable agreements are found in terms of the wake characteristics and turbine response. For instance, the azimuth variation of the mean aerodynamic forces acting on the blade was captured with a mean relative error of 15–20%. While various model-specific deficiencies could be identified, the study highlights the need for further full-scale measurement campaigns with even more extensive instrumentation. Furthermore, it is concluded that validations should not be limited to integrated and/or time-averaged quantities that conceal characteristic spatial or temporal variations.

    Place, publisher, year, edition, pages
    Elsevier, 2022
    National Category
    Fluid Mechanics and Acoustics
    Research subject
    Engineering Science
    Identifiers
    urn:nbn:se:uu:diva-468302 (URN)10.1016/j.renene.2022.04.047 (DOI)000798981500007 ()
    Available from: 2022-02-23 Created: 2022-02-23 Last updated: 2022-09-22Bibliographically approved
    7. Towards a complete model chain for ice accretion effects on wind turbines
    Open this publication in new window or tab >>Towards a complete model chain for ice accretion effects on wind turbines
    Show others...
    (English)Manuscript (preprint) (Other academic)
    National Category
    Fluid Mechanics and Acoustics
    Research subject
    Engineering Science
    Identifiers
    urn:nbn:se:uu:diva-468303 (URN)
    Available from: 2022-02-23 Created: 2022-02-23 Last updated: 2022-02-28
    8. WakeNet 0.1: A Simple Three-dimensional Wake Model Based on Convolutional Neural Networks
    Open this publication in new window or tab >>WakeNet 0.1: A Simple Three-dimensional Wake Model Based on Convolutional Neural Networks
    2022 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 2265, no 2, article id 022066Article in journal (Refereed) Published
    Abstract [en]

    Deep convolutional neural networks are a promising machine learning approach for computationally efficient predictions of flow fields. In this work we present a simple modelling framework for the prediction of the time-averaged three-dimensional flow field of wind turbine wakes. The proposed model requires the mean inflow upstream of the turbine, aerodynamic data of the turbine and the tip-speed ratio as input data. The output comprises all three mean velocity components as well as the turbulence intensity. The model is trained with the flow statistics of 900 actuator line large-eddy simulations of a single turbine in various inflow and operating conditions. The model is found to accurately predict the characteristic features of the wake flow. The overall accuracy and efficiency of the model render it as a promising approach for future wind turbine wake predictions.

    Place, publisher, year, edition, pages
    Institute of Physics Publishing (IOPP), 2022
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-468304 (URN)10.1088/1742-6596/2265/2/022066 (DOI)
    Conference
    The Science of Making Torque from Wind (TORQUE 2022), 1-3 June, Delft, Netherlands
    Available from: 2022-02-23 Created: 2022-02-23 Last updated: 2023-09-04Bibliographically approved
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  • 16.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Janßen, Christian F.
    Institute for Fluid Dynamics and Ship Theory, Hamburg University of Technology, Am Schwarzenberg-Campus 4, 21073 Hamburg, Germany.
    Olivares-Espinosa, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Wall-modeled lattice Boltzmann large-eddy simulation of neutral atmospheric boundary layers2021In: Physics of fluids, ISSN 1070-6631, E-ISSN 1089-7666, Vol. 33, no 10, p. 105111-105111Article in journal (Refereed)
    Abstract [en]

    The lattice Boltzmann method (LBM) sees a growing popularity in the field of atmospheric sciences and wind energy, largely due to itsexcellent computational performance. Still, LBM large-eddy simulation (LES) studies of canonical atmospheric boundary layer flows remainlimited. One reason for this is the early stage of development of LBM-specific wall models. In this work, we discuss LBM–LES of isothermalpressure-driven rough-wall boundary layers using a cumulant collision model. To that end, we also present a novel wall modeling approach,referred to as inverse momentum exchange method (iMEM). The iMEM enforces a wall shear stress at the off-wall grid points by adjustingthe slip velocity in bounce-back boundary schemes. In contrast to other methods, the approach does not rely on the eddy viscosity, nor doesit require the reconstruction of distribution functions. Initially, we investigate different aspects of the modeling of the wall shear stress, i.e.,an averaging of the input velocity as well as the wall-normal distance of its sampling location. Particularly, sampling locations above the firstoff-wall node are found to be an effective measure to reduce the occurring log-layer mismatch. Furthermore, we analyze the turbulence statis-tics at different grid resolutions. The results are compared to phenomenological scaling laws, experimental, and numerical references. Theanalysis demonstrates a satisfactory performance of the numerical model, specifically when compared to a well-established mixed pseudo-spectral finite difference (PSFD) solver. Generally, the study underlines the suitability of the LBM and particularly the cumulant LBM forcomputationally efficient LES of wall-modeled boundary layer flows.

    Download full text (pdf)
    fulltext
  • 17.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Janßen, Christian F.
    Hamburg University of Technology, Institute of Fluid Dynamics and Ship Theory, Hamburg .
    Olivares-Espinosa, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Nilsson, Karl
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Assessment of Weak Compressibility in Actuator Line Simulations of Wind Turbine Wakes2020In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1618, article id 062057Article in journal (Refereed)
    Abstract [en]

    The trend of increasing rotor diameters and tip-speeds has brought about concerns of non-negligible compressibility effects in wind turbine aerodynamics. The investigation of such effects on wakes is particularly difficult when using actuator line models (ALM). This is because crucial regions of the flow, i.e. the direct vicinity of the blade, are not simulated but represented by body forces. To separately assess the impact of compressibility on the wake and the ALM itself, we conduct large-eddy simulations (LES) where the forces of the ALM are prescribed and based on the local sampled velocity (standard procedure), respectively. The LES are based on the weakly-compressible Lattice Boltzmann Method (LBM). Further to the comparison of (near-)incompressible to compressible simulations we investigate cases with artificially increased compressibility. This is commonly done in weakly-compressible approaches to reduce the computational demand. The investigation with prescribed forces shows that compressibility effects in the wake flow are negligible. Small differences in the wake velocity (of max. 1%) are found to be related to local compressibility effects in the direct vicinity of the ALM. Most significantly, compressibility is found to affect the sampled velocity and thereby accuracy of the ALM.

    Download full text (pdf)
    fulltext
  • 18.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Korb, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    WakeNet 0.1: A Simple Three-dimensional Wake Model Based on Convolutional Neural Networks2022In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 2265, no 2, article id 022066Article in journal (Refereed)
    Abstract [en]

    Deep convolutional neural networks are a promising machine learning approach for computationally efficient predictions of flow fields. In this work we present a simple modelling framework for the prediction of the time-averaged three-dimensional flow field of wind turbine wakes. The proposed model requires the mean inflow upstream of the turbine, aerodynamic data of the turbine and the tip-speed ratio as input data. The output comprises all three mean velocity components as well as the turbulence intensity. The model is trained with the flow statistics of 900 actuator line large-eddy simulations of a single turbine in various inflow and operating conditions. The model is found to accurately predict the characteristic features of the wake flow. The overall accuracy and efficiency of the model render it as a promising approach for future wind turbine wake predictions.

    Download full text (pdf)
    fulltext
  • 19.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy. Carl von Ossietzky Univ Oldenburg, Inst Phys, ForWind Ctr Wind Energy Res, D-26129 Oldenburg, Germany..
    Korb, Henry
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    How Fast is Fast Enough?: Industry Perspectives on the Use of Large-eddy Simulation in Wind Energy2023In: WAKE CONFERENCE 2023 / [ed] Bottasso, C Schepers, G Larsen, G Meyers, J Uzol, O Chatelain, P Aubrun, S Leweke, T, Institute of Physics Publishing (IOPP), 2023, Vol. 2505Conference paper (Refereed)
    Abstract [en]

    The use of graphics processing units (GPUs) has facilitated unprecedented performance gains for computational fluids dynamics in recent years. In many industries this has enabled the integration of large-eddy simulation (LES) in the engineering practice. Flow modelling in the wind industry though still primarily relies on models with significantly lower fidelity. This paper seeks to investigate the reasons why wind energy applications of LES are still an exception in the industrial practice. On that account, we present a survey among industry experts on the matter. The survey shows that the large runtimes and computational costs of LES are still seen as a main obstacle. However, other reasons such as a lack of expertise and user experience, the need for more validation, and lacking trust in the potential benefits of LES reveal that computational efficiency is not the only concern. Lastly, we present an exemplary simulation of a generic offshore wind farm using a GPU-resident Lattice Boltzmann LES framework. The example shows that the runtime requirements stated by a large part of the respondents can already now be fulfilled with reasonable hardware effort.

    Download full text (pdf)
    fulltext
  • 20.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Navarro Diaz, Gonzalo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Madsen, Helge Aagard
    DTU Wind Energy, Technical University of Denmark, Frederiksborgvej 399, 4000, Roskilde, Denmark.
    Branlard, Emmanuel
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
    Meyer Forsting, Alexander R.
    DTU Wind Energy, Technical University of Denmark, Frederiksborgvej 399, 4000, Roskilde, Denmark.
    Nilsson, Karl
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Jonkman, Jason
    National Renewable Energy Laboratory, 15013 Denver West Parkway, Golden, CO, 80401, USA.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Wind Energy.
    Wind Turbine Response in Waked Inflow: A Modelling Benchmark Against Full-Scale Measurements2022In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 191, p. 868-887Article in journal (Refereed)
    Abstract [en]

    Predicting the power and loads of wind turbines in waked inflow conditions still presents a major modelling challenge. It requires the accurate modelling of the atmospheric flow conditions, wakes of upstream turbines and the response of the turbine of interest. Rigorous validations of model frameworks against measurements of utility-scale wind turbines in such scenarios remain limited to date. In this study, six models of different fidelity are compared against measurements from the DanAero experiment. The two benchmark cases feature a full-wake and partial-wake scenario, respectively. The simulations are compared against local pressure forces and inflow velocities measured on several blade sections of the downstream turbine, as well as met mast measurements and standard SCADA data. Regardless of the model fidelity, reasonable agreements are found in terms of the wake characteristics and turbine response. For instance, the azimuth variation of the mean aerodynamic forces acting on the blade was captured with a mean relative error of 15–20%. While various model-specific deficiencies could be identified, the study highlights the need for further full-scale measurement campaigns with even more extensive instrumentation. Furthermore, it is concluded that validations should not be limited to integrated and/or time-averaged quantities that conceal characteristic spatial or temporal variations.

    Download full text (pdf)
    fulltext
  • 21.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Olivares-Espinosa, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Actuator line simulations of wind turbine wakes using the lattice Boltzmann method2020In: Wind Energy Science, ISSN 2366-7443, E-ISSN 2366-7451, Vol. 5, no 2, p. 623-645Article in journal (Refereed)
    Abstract [en]

    The high computational demand of large-eddy simulations (LESs) remains the biggest obstacle for a wider applicability of the method in the field of wind energy. Recent progress of GPU-based (graphics processing unit) lattice Boltzmann frameworks provides significant performance gains alleviating such constraints. The presented work investigates the potential of LES of wind turbine wakes using the cumulant lattice Boltzmann method (CLBM). The wind turbine is represented by the actuator line model (ALM). The implementation is validated and discussed by means of a code-to-code comparison to an established finite-volume Navier–Stokes solver. To this end, the ALM is subjected to both laminar and turbulent inflow while a standard Smagorinsky sub-grid-scale model is employed in the two numerical approaches. The resulting wake characteristics are discussed in terms of the first- and second-order statistics as well the spectra of the turbulence kinetic energy. The near-wake characteristics in laminar inflow are shown to match closely with differences of less than 3 % in the wake deficit. Larger discrepancies are found in the far wake and relate to differences in the point of the laminar-turbulent transition of the wake. In line with other studies, these differences can be attributed to the different orders of accuracy of the two methods. Consistently better agreement is found in turbulent inflow due to the lower impact of the numerical scheme on the wake transition. In summary, the study outlines the feasibility of wind turbine simulations using the CLBM and further validates the presented set-up. Furthermore, it highlights the computational potential of GPU-based LBM implementations for wind energy applications. For the presented cases, near-real-time performance was achieved using a single, off-the-shelf GPU on a local workstation.

    Download full text (pdf)
    fulltext
  • 22.
    Asmuth, Henrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Olivares-Espinosa, Hugo
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Nilsson, Karl
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Ivanell, Stefan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    The Actuator Line Model in Lattice Boltzmann Frameworks: Numerical Sensitivity and Computational Performance2019In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 1256, article id 012022Article in journal (Refereed)
    Abstract [en]

    The growing use of large-eddy simulations for the modelling of wind farms makes the need for efficient numerical frameworks more essential than ever. GPU-accelerated implementations of the Lattice Boltzmann Method (LBM) have shown to provide significant performance gains over classical Navier-Stokes-based computational fluid dynamics. Yet, their use in the field of wind energy remains limited to date. In this fundamental study the cumulant LBM is scrutinised for actuator line simulations of wind turbines. The numerical sensitivity of the method in a simple uniform inflow is investigated with respect to spatial and temporal resolution as well as the width of the actuator line’s regularisation kernel. Comparable accuracy and slightly better stability properties are shown in relation to a standard Navier-Stokes implementation. The results indicate the overall suitability of the cumulant LBM for wind turbine wake simulations. The potential of the LBM for future wind energy applications is clarified by means of a brief comparison of computational performance.

    Download full text (pdf)
    fulltext
  • 23.
    Augustin, Xenia
    et al.
    ETH Zurich.
    Zhang, Lin
    ETH Zurich.
    Goksel, Orcun
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction. ETH Zurich.
    Estimating Mean Speed-of-Sound from Sequence-Dependent Geometric Disparities2021Conference paper (Refereed)
  • 24.
    Baudoin, Antoine
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saury, Didier
    Univ Poitiers, ENSMA, CNRS, Inst PPRIME, BP 40109, F-86961 Futuroscope, France.
    Temperature and velocity measurements in a buoyant flow induced by a heat source array on a vertical plate2017In: Experimental Thermal and Fluid Science, ISSN 0894-1777, E-ISSN 1879-2286, Vol. 88, p. 234-245Article in journal (Refereed)
    Abstract [en]

    Heat source arrays are common in engineering applications. Natural convection is a reliable and silent cooling strategy. Therefore, an array of flush-mounted heat sources has been studied under conjugate conduction and natural convection condition. This studies was performed for a system with relatively large dimensions, typical for power electronics, and a modified Rayleigh number up to 2 . 10(10) A modular set of heaters was designed to vary the distribution of heat sources on the plate and investigate the influence of the spacing. Velocity and temperature were measured in the convective flow with particle image velocimetry and micro-thermocouple. The velocity field was analyzed with proper orthogonal decomposition. The first instabilities of the convective flows were described. The results gave abetter understanding of the heat transfers in these configurations and are valuable for model validation.

  • 25.
    Berglund, Albin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Evolution of Cavity Tip Vortices in High-Pressure Turbines2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    This degree project in applied physics studies the tip gap flows over the rotor blades of a high-pressure turbine. The rotor blade used in the study has an improved design that utilizes both a cavity tip and an uneven profiling to reduce turbine loss. The designed rotor blade is shown to admit a 21% lower leakage mass flow rate across the tip gap than a reference rotor blade with a flat tip. By studying the designed rotor blade using transient CFD, the flow field of the tip gap region has been studied through one blade passage. The flow field characteristics of particular interest are the leakage mass flow rate across the tip gap region, which is proportional to turbine loss, and the characteristic vortices that reside within the cavity tip. By using post-processing scripts, the leakage mass flow rate has been calculated for every time step across one blade passage, showing a strong time dependence. The characteristic vortices are found using two different vortex detection algorithms, and their respective vorticity magnitude is shown to depend on the leakage mass flow rate. The simulation shows that the vorticity magnitude is increasing above a threshold of leakage mass flow rate, and that it is decreasing under this threshold. This effect is shown to destabilize the leakage mass flow rate, increasing its amplitude over its period of one blade passage.

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    Evolution of Cavity Tip Vortices in High-Pressure Turbines
  • 26.
    Bergstrand, David
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Investigation of Internal Diesel Injector Deposits on fuel injector performance for proposal of injector test rig test method.2020Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With increasing demands for lowering emissions from diesel engines, bio fuel has been introduced to the fuel mixture. This fuel is based on vegetable oil with a much smaller carbon footprint than fossil fuel. The chemical composition of bio fuel has lead to deposits forming inside the fuel injector in diesel engines, these deposits are usually denoted as Internal Diesel Injector Deposits (IDID). At Scania CV AB an injector test rig is designed with the goal of creating and investigating IDID. This project has made a theoretical investigation of how IDID are formed and how this affects the mechanics inside the injector. It has also analysed injector components from a worst case scenario perspective in order to find a testing method for creating IDID in the test rig. By analysing performance changes from a build-up perspective, where IDID decreases the tolerances inside the injector, as well as friction, formed when deposits cause injector mechanics to stick together, it has been found that injector performance does hardly change from build-up and that performance changes only occur when friction is introduced. From the injector component analysis it is found that the limiting factors in rig testing come from fuel system components rather than the injector itself. This is the base for a rig running test method presented.

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    fulltext
  • 27. Birken, Philipp
    et al.
    Bull, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Jameson, Antony
    A study of multigrid smoothers used in compressible CFD based on the convection diffusion equation2016In: Proc. 7th ECCOMAS Congress, European Community on Computional Methods in Applied Sciences (ECCOMAS), 2016, p. 2648-2663Conference paper (Refereed)
  • 28. Birken, Philipp
    et al.
    Bull, Jonathan
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Scientific Computing. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Numerical Analysis.
    Jameson, Antony
    Preconditioned smoothers for the Full Approximation Scheme for the RANS equations2019In: Journal of Scientific Computing, ISSN 0885-7474, E-ISSN 1573-7691, Vol. 78, p. 995-1022Article in journal (Refereed)
  • 29.
    Blomström, Hanna
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Effektiviseringspotential inom industrisektorn: Energibesparing vid frekvensstyrning av centrifugalpumpar – en fallstudie2013Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The project was performed at Siemens

    Industry Drive Technologies with the

    objective to provide actual values for

    the energy savings potential within

    Siemens scope of practice.

    In Sweden the electrical drives stand

    for about 30 % of the total electricity

    consumption and about 60 % of the

    electricity consumption within the

    industry. During the pre-study phase

    electrical drives with pump applications

    were identified as large energy users.

    Because of this a case study at one of

    Siemens customers, Stora Enso Fors was

    performed. The system that was evaluated

    during the case study was a throttled

    system with a centrifugal pump for

    pumping pulp.

    The results yielded that a saving of

    over 50 % could be achieved by replacing

    the throttle valve with a variable speed

    drive, a frequency converter. The

    payback period was two years and two

    months and the present value for the

    total life cycle cost of the variable

    speed system was 662.566 SEK lower than

    for the throttled system. As a

    consequence, Stora Enso Fors is advised

    to invest in a frequency converter for

    regulation of the system.

    The general conclusion is that a focus

    on system efficiency is the most

    important factor in energy efficiency

    projects and that the system regulation

    method has a large impact on the overall

    system losses and hence its efficiency.

    Energy efficiency potential for

    throttled systems with centrifugal pumps

    is large and significant economical

    savings can be made through investments

    with short payback time.

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  • 30.
    Bolin, Karl
    et al.
    Kungliga Tekniska Hgsk, Marcus Wallenberg Lab, SE-10044 Stockholm, Sweden..
    Conrady, Kristina
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Karasalo, Ilkka
    Kungliga Tekniska Hgsk, Marcus Wallenberg Lab, SE-10044 Stockholm, Sweden..
    Sjöblom, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    An investigation of the influence of the refractive shadow zone on wind turbine noise2020In: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 148, no 2, p. EL166-EL171Article in journal (Refereed)
    Abstract [en]

    This article aims to investigate if the proportion of the rotor area of a wind turbine that is in the refractive shadow zone according to a ray tracing algorithm coupled to meteorological forecast data is correlated to sound levels and amplitude modulation. The acoustic station is situated 950 m from a wind farm in Northern Sweden and the measurement period is seven months. On average, 1.9 dBA lower sound levels are measured when the part of the rotor disk of the closest turbine is in the refractive shadow zone. A higher probability of amplitude modulations are observed when around half of the turbine rotor is within the refractive shadow zone compared to conditions with no shadow zone present.

  • 31.
    Bull, Jonathan
    et al.
    Stanford University.
    Jameson, Antony
    High-Order Flux Reconstruction Schemes for LES on Tetrahedral Meshes2014In: Progress in Hybrid RANS-LES Modelling: Volume 130 of the series Notes on Numerical Fluid Mechanics and Multidisciplinary Design / [ed] Sharath Girimaji, Werner Haase, Shia-Hui Peng, Dieter Schwamborn, 2014Conference paper (Refereed)
    Abstract [en]

    The use of the high-order Flux Reconstruction (FR) spatial discretization scheme for LES on unstructured meshes is investigated. Simulations of the compressible Taylor-Green vortex at Re=1,600 demonstrate that the FR scheme has low numerical dissipation and accurately reproduces the turbulent energy cascade at low resolution, making it ideal for high-order LES. To permit the use of subgrid-scale models incorporating explicit filtering on tetrahedral meshes, a high-order filter acting on the modal form of the solution (i.e. the Dubiner basis functions) is developed. The WALE-Similarity mixed (WSM) model using this filter is employed for LES of the flow over a square cylinder at Re=21,400, obtaining reasonable agreement with experiments. Future research will be directed at improved SGS models and filters and at developing high-order hybrid RANS/LES methods.

  • 32.
    Bull, Jonathan
    et al.
    Applied Modelling and Computation Group, Department of Earth Science and Engineering, Imperial College London, London, UK.
    Piggott, Matthew
    Imperial College London.
    Pain, Christopher
    Imperial College London.
    A finite element LES methodology for anisotropic inhomogeneous meshes2012In: Proceedings of the Seventh International Symposium On Turbulence, Heat and Mass Transfer Palermo, Italy, 24-27 September, 2012, Begell House, 2012Conference paper (Refereed)
    Abstract [en]

    Large eddy simulation techniques offer a wealth of valuable information for engineering design purposes, but in many cases the required mesh resolution is prohibitive. Combining the dynamic LES procedure with unstructured mesh adaptivity offers a robust and efficient way of capturing the inhomogeneity and anisotropy of complex turbulent flows. However, this may result in a non-vanishing commutation error due to the filter employed. The inverse Helmholtz filter is used here with a tensor definition of filter width related to the local element size and shape. The formulation, verification and validation of a finite element methodology, designed to yield maximal accuracy from moderate mesh resolution with minimal ad hoc procedures, is described. Results for the 3D backward facing step obtained using the open source CFD code Fluidity are presented. Using adaptive meshing, closer agreement to DNS was obtained compared to fixed meshes while using 60% fewer nodes.

  • 33.
    Burman, Jan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Swedish Def Res Agcy, FOI, Div CBRN Def & Secur, S-90182 Umea, Sweden.
    Jonsson, Lage
    Swedish Def Res Agcy, FOI, Div CBRN Def & Secur, S-90182 Umea, Sweden;Royal Inst Technol, KTH, S-10044 Stockholm, Sweden.
    Rutgersson, Anna
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    On possibilities to estimate local concentration variations with CFD-LES in real urban environments2019In: Environmental Fluid Mechanics, ISSN 1567-7419, E-ISSN 1573-1510, Vol. 19, no 3, p. 719-750Article in journal (Refereed)
    Abstract [en]

    Applied studies with Large Eddy Simulation (LES) of hazardous gas dispersion around buildings in cities have become increasingly feasible due to rapid advancements in computing technology. However, there is little extant literature investigating how each model's results compare with others, as well as their ability to predict near-field dispersion in a real city. In this study, three typical LES sub-grid-scale models are used to simulate gas dispersion, utilizing alternatively constant values and synthetic turbulence at inflow boundaries. The results are compared with data from the Joint Urban 2003 Atmospheric Dispersion Study in Oklahoma City. Flow and turbulence statistics of the simulation is presented at two probe locations, one inside the city-core and one outside. In addition, comparisons with the measured mean concentration and maximum concentration values are conducted. It was found that in the core of the city, simulated turbulence is mainly determined by buildings and their configurations, and is only weakly affected by model type and assumed turbulence at the inflow boundaries. On the other hand, outside and upwind the city center the turbulence set at the inflow boundaries is very important if realistic turbulence statistics is to be achieved. Downstream of the source, all tested models produce similar predictions of maximum concentration values, which in turn are similar to the experimental data. Thus, the results indicate that it could be better to use the LES calculated maximum-concentration instead of the calculated mean-concentration when developing methods for hazard area estimation.

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    FULLTEXT01
  • 34.
    Cai, Tengfei
    et al.
    Univ Sci & Technol Beijing, Sch Mech Engn, Beijing 100083, Peoples R China.;Univ Illinois, Dept Mech Sci & Engn, Urbana, IL 61801 USA..
    Cheng, Shyuan
    Univ Illinois, Dept Mech Sci & Engn, Urbana, IL 61801 USA..
    Segalini, Antonio
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Chamorro, Leonardo P.
    Univ Illinois, Dept Mech Sci & Engn, Urbana, IL 61801 USA.;Univ Illinois, Dept Aerosp Engn, Urbana, IL 61801 USA.;Univ Illinois, Dept Civil & Environm Engn, Urbana, IL 61801 USA.;Univ Illinois, Dept Geol, Urbana, IL 61801 USA..
    Local topography-induced pressure gradient effects on the wake and power output of a model wind turbine2021In: Theoretical and Applied Mechanics Letters, ISSN 2095-0349, Vol. 11, no 5, article id 100297Article in journal (Refereed)
    Abstract [en]

    Wind-tunnel experiments were performed to study the effect of favorable and adverse constant pressure gradients (PG) from local changes in the topography right downwind of a model wind turbine. Particle image velocimetry was used to characterize the near and intermediate wake regions. We explored five scenarios, two favorable, two adverse PG, and a case with negligible PG. Results show that the PGs induce a wake deflection and modulate the wake. They imposed a relatively small impact on the turbulence kinetic energy and kinematic shear stress but a comparatively dominant effect on the bulk flow on the flow recovery. Based on this, a simple formulation is used to describe the impact of PG on the wake. We modeled the base flow through a linearized perturbation method; the wake is obtained by solving a simplified, integrated streamwise momentum equation. This approach reasonably estimated the flow profile and PG-induced power output variations. (C) 2021 The Authors. Published by Elsevier Ltd on behalf of The Chinese Society of Theoretical and Applied Mechanics.

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  • 35.
    Chang, Bo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Shah, Ali
    Aalto University.
    Zhou, Quan
    Aalto University.
    Ras, Robin
    Aalto University.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Self-transport and self-alignment of microchips using microscopic rain2015In: Scientific Reports, E-ISSN 2045-2322, Vol. 5, article id 14966Article in journal (Refereed)
    Abstract [en]

    Alignment of microchips with receptors is an important process step in the construction of integrated micro- and nanosystems for emerging technologies, and facilitating alignment by spontaneous self-assembly processes is highly desired. Previously, capillary self-alignment of microchips driven by surface tension effects on patterned surfaces has been reported, where it was essential for microchips to have sufficient overlap with receptor sites. Here we demonstrate for the first time capillary self-transport and self-alignment of microchips, where microchips are initially placed outside the corresponding receptor sites and can be self-transported by capillary force to the receptor sites followed by self-alignment. The surface consists of hydrophilic silicon receptor sites surrounded by superhydrophobic black silicon. Rain-induced microscopic droplets are used to form the meniscus for the self-transport and self-alignment. The boundary conditions for the self-transport have been explored by modeling and confirmed experimentally. The maximum permitted gap between a microchip and a receptor site is determined by the volume of the liquid and by the wetting contrast between receptor site and substrate. Microscopic rain applied on hydrophilic-superhydrophobic patterned surfaces greatly improves the capability, reliability and error-tolerance of the process, avoiding the need for accurate initial placement of microchips, and thereby greatly simplifying the alignment process.

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  • 36.
    Chang, Bo
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Zhou, Quan
    Aalto University, Finland.
    Ras, Robin
    Aalto University, Finland.
    Shah, Ali
    Aalto University, Finland.
    Wu, Zhigang
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Sliding droplets on hydrophilic/superhydrophobic patterned surfaces for liquid deposition2016In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 108, no 15, article id 154102Article in journal (Refereed)
    Abstract [en]

    A facile gravity-induced sliding droplets method is reported for deposition of nanoliter sized droplets on hydrophilic/superhydrophobic patterned surface. The deposition process is parallel where multiple different liquids can be deposited simultaneously. The process is also high-throughput, having a great potential to be scaled up by increasing the size of the substrate.

  • 37.
    Chintada, Bhaskara R.
    et al.
    ETH Zurich.
    Rau, Richard
    ETH Zurich.
    Goksel, Orcun
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Visual Information and Interaction. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction. Computer-assisted Applications in Medicine, ETH Zurich, Zurich, Switzerland.
    Phase-Aberration Correction in Shear-Wave Elastography Imaging Using Local Speed-of-Sound Adaptive Beamforming2021In: Frontiers in Physics, E-ISSN 2296-424X, Vol. 9, article id 690385Article in journal (Refereed)
    Abstract [en]

    Shear wave elasticity imaging (SWEI) is a non-invasive imaging modality that provides tissue elasticity information by measuring the travelling speed of an induced shear-wave. It is commercially available on clinical ultrasound scanners and popularly used in the diagnosis and staging of liver disease and breast cancer. In conventional SWEI methods, a sequence of acoustic radiation force (ARF) pushes are used for inducing a shear-wave, which is tracked using high frame-rate multi-angle plane wave imaging (MA-PWI) to estimate the shear-wave speed (SWS). Conventionally, these plane waves are beamformed using a constant speed-of-sound (SoS), assuming an a-priori known and homogeneous tissue medium. However, soft tissues are inhomogeneous, with intrinsic SoS variations. In this work, we study the SoS effects and inhomogeneities on SWS estimation, using simulation and phantoms experiments with porcine muscle as an abbarator, and show how these aberrations can be corrected using local speed-of-sound adaptive beamforming. For shear-wave tracking, we compare standard beamform with spatially constant SoS values to software beamforming with locally varying SoS maps. We show that, given SoS aberrations, traditional beamforming using a constant SoS, regardless of the utilized SoS value, introduces a substantial bias in the resulting SWS estimations. Average SWS estimation disparity for the same material was observed over 4.3 times worse when a constant SoS value is used compared to that when a known SoS map is used for beamforming. Such biases are shown to be corrected by using a local SoS map in beamforming, indicating the importance of and the need for local SoS reconstruction techniques.

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  • 38.
    Cruz, F. Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
    High pressure inertial focusing: integration in parallel and series2018Conference paper (Other academic)
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    JC_MSW2018
  • 39.
    Cruz, Javier
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Microfluidics for High-Pressure Inertial Focusing: Focusing, Separation and Concentration of Micro and Sub-micron Particles2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The birth of microsystems set the ground for technologies never imagined before, for it is not only the small size what characterizes the miniaturized systems, but unique phenomena arise in the micro scale. This thesis relates to one such unique phenomenon, inertial focusing, a phenomenon that occurs in microfluidic systems if very special conditions are met and that allows for fine manipulation of particles in fluid samples. This ability is key in a bigger picture: the analysis of complex fluids, where rare particles of interest may be present in very few numbers amongst a myriad of others, making the task difficult – if not impossible. A system exploiting inertial focusing allows, for instance, to focus, separate, isolate and concentrate such rare particles of interest, and even to transfer them to another fluid, thereby enabling/facilitating their detection and analysis. Examples of rare particles of interest in complex fluids are circulating tumor cells in blood, that give away the presence of cancer, extracellular vesicles also in blood, that contain biomarkers with physiological and pathological information about the patient, or bacteria in natural water, where the species present and their numbers are to be monitored for safety reasons and/or biological studies. This thesis covers the state of art physical principles behind the phenomenon and extends the understanding both in theory and applications. Specifically, the technology is extended to allow for manipulation of sub-micron particles, a range of interest as it comprises bacteria, viruses and organelles of eukaryotic cells. This was possible by an analysis of the balance of forces in play and by the integration of inertial focusing in high-pressure systems (up to 200 bar). In a second block, a very special line of inertial focusing is introduced and developed; inertial focusing in High Aspect Ratio Curved (HARC) microfluidics. These systems, engineered to rearrange the force field responsible for the particle manipulation, not only achieve excellent performances for focusing and concentration of particles, but also extreme resolution in their separation (mathematically unlimited; demonstrated experimentally for differences in size down to 80 nm). Perhaps more important than the performance, the systems are stable, intuitive and simpler to design, attributes that we hope will make the technology and its outstanding benefits more accessible to the community. With its remarkable performance, it would not come as a surprise if, in the near future, inertial focusing makes a strong impact on how analyses are performed nowadays and opens up for possibilities beyond the current state of the art.

    List of papers
    1. High pressure inertial focusing for separating and concentrating bacteria at high throughput
    Open this publication in new window or tab >>High pressure inertial focusing for separating and concentrating bacteria at high throughput
    Show others...
    2017 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 27, no 8, article id 084001Article in journal (Refereed) Published
    Abstract [en]

    Inertial focusing is a promising microfluidic technology for concentration and separation of particles by size. However, there is a strong correlation of increased pressure with decreased particle size. Theory and experimental results for larger particles were used to scale down the phenomenon and find the conditions that focus 1 mu m particles. High pressure experiments in robust glass chips were used to demonstrate the alignment. We show how the technique works for 1 mu m spherical polystyrene particles and for Escherichia coli, not being harmful for the bacteria at 50 mu l min(-1). The potential to focus bacteria, simplicity of use and high throughput make this technology interesting for healthcare applications, where concentration and purification of a sample may be required as an initial step.

    Place, publisher, year, edition, pages
    IOP PUBLISHING LTD, 2017
    Keywords
    bacteria separation, particle separation, inertial focusing, high pressure, glass chips, PDMS, microfluidic channel
    National Category
    Condensed Matter Physics Other Materials Engineering Analytical Chemistry Physical Chemistry
    Identifiers
    urn:nbn:se:uu:diva-329919 (URN)10.1088/1361-6439/aa6b14 (DOI)000404540500001 ()
    Funder
    EU, Horizon 2020, 644669
    Available from: 2018-02-22 Created: 2018-02-22 Last updated: 2020-12-07Bibliographically approved
    2. Inertial focusing with sub-micron resolution for separation of bacteria
    Open this publication in new window or tab >>Inertial focusing with sub-micron resolution for separation of bacteria
    2019 (English)In: Lab on a Chip, ISSN 1473-0197, E-ISSN 1473-0189, Vol. 19, no 7, p. 1257-1266Article in journal (Refereed) Published
    Abstract [en]

    In this paper, we study inertial focusing in curved channels and demonstrate the alignment of particles with diameters between 0.5 and 2.0 m, a range of biological relevance since it comprises a multitude of bacteria and organelles of eukaryotic cells. The devices offer very sensitive control over the equilibrium positions and allow two modes of operation. In the first, particles having a large variation in size are focused and concentrated together. In the second, the distribution spreads in a range of sizes achieving separation with sub-micron resolution. These systems were validated with three bacteria species (Escherichia coli, Salmonella typhimurium and Klebsiella pneumoniae) showing good alignment while maintaining the viability in all cases. The experiments also revealed that the particles follow a helicoidal trajectory to reach the equilibrium positions, similar to the fluid streamlines simulated in COMSOL, implying that these positions occupy different heights in the cross section. When the equilibrium positions move to the inner wall as the flow rate increases, they are at a similar distance from the centre than in straight channels (approximate to 0.6R), but when the equilibrium positions move to the outer wall as the flow rate increases, they are closer to the centre and the particles pass close to the inner wall to elevate their position before reaching them. These observations were used along with COMSOL simulations to explain the mechanism behind the local force balance and the migration of particles, which we believe contributes to further understanding of the phenomenon. Hopefully, this will make designing more intuitive and reduce the high pressure demands, enabling manipulation of particles much smaller than a micrometer.

    Place, publisher, year, edition, pages
    ROYAL SOC CHEMISTRY, 2019
    National Category
    Biochemistry and Molecular Biology
    Identifiers
    urn:nbn:se:uu:diva-382383 (URN)10.1039/c9lc00080a (DOI)000462723900009 ()30821308 (PubMedID)
    Funder
    EU, Horizon 2020, 644669
    Available from: 2019-04-25 Created: 2019-04-25 Last updated: 2020-12-07Bibliographically approved
    3. Stable 3D Inertial Focusing by High Aspect Ratio Curved Microfluidics
    Open this publication in new window or tab >>Stable 3D Inertial Focusing by High Aspect Ratio Curved Microfluidics
    2021 (English)In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 31, article id 015008Article in journal (Refereed) Published
    Abstract [en]

    Fine manipulation of particles is essential for the analysis of complex samples such as blood or environmental water, where rare particles of interest may be masked by millions of others. Inertial focusing is amongst the most promising techniques for this task, enabling label-free manipulation of particles with sub-micron resolution at very high flow rates. However, the phenomenon still remains difficult to predict due to the focus position shifting in tortuous ways as function of the channel geometry, flow rate and particle size. Here, we present a new line of microfluidics that exploit inertial focusing in High Aspect Ratio Curved (HARC) microchannels and overcome this limitation. Consisting of a single curved channel, HARC systems provide a highly predictable, single focus position near the centre of the inner wall, largely independent of the flow rate and particle size.

    An explanation of the mechanism of migration and focus of particles, together with its governing equations, is provided based on simulations in COMSOL Multiphysics and experimental results. HARC microchannels built in silicon-glass were used for experimental validation, achieving a high quality, single focus position for a range of microparticles with sizes of 0.7 - 1 µm and bacterial cells (Escherichia coli). The recovery of 1 µm particles was 99.84% with a factor four in concentration.

    With a stable focus position, we envision that HARC systems will bring the technology closer to implementation in laboratories for analysis of complex fluids with biological particles like cells and organelles.

    Place, publisher, year, edition, pages
    Institute of Physics Publishing (IOPP), 2021
    Keywords
    Microfluidics, Particle manipulation, Inertial Focusing
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-427307 (URN)10.1088/1361-6439/abcae7 (DOI)000595695600001 ()
    Available from: 2020-12-06 Created: 2020-12-06 Last updated: 2024-01-15Bibliographically approved
    4. Fundamentals of Inertial Focusing in High Aspect Ratio Curved Microfluidics
    Open this publication in new window or tab >>Fundamentals of Inertial Focusing in High Aspect Ratio Curved Microfluidics
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    Microfluidics exploiting the phenomenon of inertial focusing have attracted much attention in the last decade, as they provide the means to facilitate the detection and analysis of rare particles of interest in complex fluids such as blood and natural water. Although many interesting applications have been demonstrated, the systems remain difficult to engineer. A recently presented line of the technology, inertial focusing in High Aspect Ration Curved (HARC) microfluidics, has the potential to change this and make the benefits of inertial focusing more accessible to the community. In this paper, with experimental evidence and fluid simulations, we provide the two necessary equations to design the systems and successfully focus the desired targets in a single, stable, and high-quality position. Last, the experiments revealed an interesting scaling law of the lift force, which we believe provides a valuable insight into the phenomenon of inertial microfluidics.

    Keywords
    Microfluidics, Particle manipulation, Inertial Focusing
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-427308 (URN)
    Available from: 2020-12-06 Created: 2020-12-06 Last updated: 2021-01-28Bibliographically approved
    5. High-resolution Particle Separation by Inertial Focusing in High Aspect Ratio Curved Microfluidics
    Open this publication in new window or tab >>High-resolution Particle Separation by Inertial Focusing in High Aspect Ratio Curved Microfluidics
    (English)Manuscript (preprint) (Other academic)
    Abstract [en]

    The ability to focus, separate and concentrate specific targets in a fluid is essential for the analysis of complex samples such as biological fluids, where a myriad of different particles may be present. Inertial focusing is a very promising technology for such tasks. Recently, inertial focusing in High Aspect Ratio Curved (HARC) microchannels was presented, which simplifies the focusing and concentration of targets by positioning particles close together over a wide range of particle size and flow rate. However, by focusing all particles together, HARC systems lose an essential feature of inertial focusing: the possibility of particle separation by size. Within this work, we report that HARC systems not only do have the capacity to separate particles but can do so with extremely high resolution, which we demonstrate for particles with a size difference down to 80 nm.

    A model considering the main flow, the secondary flow and a simplified expression for the lift force in HARC microchannels was developed and proven accurate for the prediction of the performance of the systems. The concept was also demonstrated experimentally with three different sub-micron particles (0.79, 0.92 and 1.0 µm in diameter) in silicon-glass microchannels, whose separation distance could be modulated by the radius of the channel.

    With the capacity to focus sub-micron particles and to separate them with high resolution, inertial focusing in HARC systems are a technology with a strong potential for particle manipulation. We believe that this will facilitate the analysis of complex fluid samples containing bioparticles like bacteria, viruses or eukaryotic organelles.

    Keywords
    Microfluidics, Particle manipulation, Inertial Focusing
    National Category
    Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-427309 (URN)
    Available from: 2020-12-06 Created: 2020-12-06 Last updated: 2021-01-28Bibliographically approved
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  • 40.
    Cruz, Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Hjort, Karin
    Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Medicine, Department of Medical Biochemistry and Microbiology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Stable 3D Inertial Focusing by High Aspect Ratio Curved Microfluidics2021In: Journal of Micromechanics and Microengineering, ISSN 0960-1317, E-ISSN 1361-6439, Vol. 31, article id 015008Article in journal (Refereed)
    Abstract [en]

    Fine manipulation of particles is essential for the analysis of complex samples such as blood or environmental water, where rare particles of interest may be masked by millions of others. Inertial focusing is amongst the most promising techniques for this task, enabling label-free manipulation of particles with sub-micron resolution at very high flow rates. However, the phenomenon still remains difficult to predict due to the focus position shifting in tortuous ways as function of the channel geometry, flow rate and particle size. Here, we present a new line of microfluidics that exploit inertial focusing in High Aspect Ratio Curved (HARC) microchannels and overcome this limitation. Consisting of a single curved channel, HARC systems provide a highly predictable, single focus position near the centre of the inner wall, largely independent of the flow rate and particle size.

    An explanation of the mechanism of migration and focus of particles, together with its governing equations, is provided based on simulations in COMSOL Multiphysics and experimental results. HARC microchannels built in silicon-glass were used for experimental validation, achieving a high quality, single focus position for a range of microparticles with sizes of 0.7 - 1 µm and bacterial cells (Escherichia coli). The recovery of 1 µm particles was 99.84% with a factor four in concentration.

    With a stable focus position, we envision that HARC systems will bring the technology closer to implementation in laboratories for analysis of complex fluids with biological particles like cells and organelles.

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  • 41.
    Cruz, Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Fundamentals of Inertial Focusing in High Aspect Ratio Curved MicrofluidicsManuscript (preprint) (Other academic)
    Abstract [en]

    Microfluidics exploiting the phenomenon of inertial focusing have attracted much attention in the last decade, as they provide the means to facilitate the detection and analysis of rare particles of interest in complex fluids such as blood and natural water. Although many interesting applications have been demonstrated, the systems remain difficult to engineer. A recently presented line of the technology, inertial focusing in High Aspect Ration Curved (HARC) microfluidics, has the potential to change this and make the benefits of inertial focusing more accessible to the community. In this paper, with experimental evidence and fluid simulations, we provide the two necessary equations to design the systems and successfully focus the desired targets in a single, stable, and high-quality position. Last, the experiments revealed an interesting scaling law of the lift force, which we believe provides a valuable insight into the phenomenon of inertial microfluidics.

  • 42.
    Cruz, Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    High-resolution Particle Separation by Inertial Focusing in High Aspect Ratio Curved MicrofluidicsManuscript (preprint) (Other academic)
    Abstract [en]

    The ability to focus, separate and concentrate specific targets in a fluid is essential for the analysis of complex samples such as biological fluids, where a myriad of different particles may be present. Inertial focusing is a very promising technology for such tasks. Recently, inertial focusing in High Aspect Ratio Curved (HARC) microchannels was presented, which simplifies the focusing and concentration of targets by positioning particles close together over a wide range of particle size and flow rate. However, by focusing all particles together, HARC systems lose an essential feature of inertial focusing: the possibility of particle separation by size. Within this work, we report that HARC systems not only do have the capacity to separate particles but can do so with extremely high resolution, which we demonstrate for particles with a size difference down to 80 nm.

    A model considering the main flow, the secondary flow and a simplified expression for the lift force in HARC microchannels was developed and proven accurate for the prediction of the performance of the systems. The concept was also demonstrated experimentally with three different sub-micron particles (0.79, 0.92 and 1.0 µm in diameter) in silicon-glass microchannels, whose separation distance could be modulated by the radius of the channel.

    With the capacity to focus sub-micron particles and to separate them with high resolution, inertial focusing in HARC systems are a technology with a strong potential for particle manipulation. We believe that this will facilitate the analysis of complex fluid samples containing bioparticles like bacteria, viruses or eukaryotic organelles.

  • 43.
    Cruz, Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    High-resolution particle separation by inertial focusing in high aspect ratio curved microfluidics2021In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, article id 13959Article in journal (Refereed)
    Abstract [en]

    The ability to focus, separate and concentrate specific targets in a fluid is essential for the analysis of complex samples such as biological fluids, where a myriad of different particles may be present. Inertial focusing is a very promising technology for such tasks, and specially a recently presented variant, inertial focusing in High Aspect Ratio Curved systems (HARC systems), where the systems are easily engineered and focus the targets together in a stable position over a wide range of particle sizes and flow rates. However, although convenient for laser interrogation and concentration, by focusing all particles together, HARC systems lose an essential feature of inertial focusing: the possibility of particle separation by size. Within this work, we report that HARC systems not only do have the capacity to separate particles but can do so with extremely high resolution, which we demonstrate for particles with a size difference down to 80 nm. In addition to the concept for particle separation, a model considering the main flow, the secondary flow and a simplified expression for the lift force in HARC microchannels was developed and proven accurate for the prediction of the performance of the systems. The concept was also demonstrated experimentally with three different sub-micron particles (0.79, 0.92 and 1.0 mu m in diameter) in silicon-glass microchannels, where the resolution in the separation could be modulated by the radius of the channel. With the capacity to focus sub-micron particles and to separate them with high resolution, we believe that inertial focusing in HARC systems is a technology with the potential to facilitate the analysis of complex fluid samples containing bioparticles like bacteria, viruses or eukaryotic organelles.

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    FULLTEXT01
  • 44.
    Cruz, Javier
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Hjort, Klas
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    The upper limit and lift force within inertial focusing in high aspect ratio curved microfluidics2021In: Scientific Reports, E-ISSN 2045-2322, Vol. 11, no 1, article id 6473Article in journal (Refereed)
    Abstract [en]

    Microfluidics exploiting the phenomenon of inertial focusing have attracted much attention in the last decade as they provide the means to facilitate the detection and analysis of rare particles of interest in complex fluids such as blood and natural water. Although many interesting applications have been demonstrated, the systems remain difficult to engineer. A recently presented line of the technology, inertial focusing in High Aspect Ratio Curved microfluidics, has the potential to change this and make the benefits of inertial focusing more accessible to the community. In this paper, with experimental evidence and fluid simulations, we provide the two necessary equations to design the systems and successfully focus the targets in a single, stable, and high-quality position. The experiments also revealed an interesting scaling law of the lift force, which we believe provides a valuable insight into the phenomenon of inertial focusing.

    Download full text (pdf)
    FULLTEXT01
  • 45.
    Decuyper, J.
    et al.
    Vrije Univ Brussel, Dept Engn Technol INDI, Pl Laan 2, B-1050 Brussels, Belgium.;Vrije Univ Brussel, Thermo & Fluid Dynam FLOW, Pl Laan 2, B-1050 Brussels, Belgium..
    De Troyer, T.
    Vrije Univ Brussel, Dept Engn Technol INDI, Pl Laan 2, B-1050 Brussels, Belgium.;Vrije Univ Brussel, Thermo & Fluid Dynam FLOW, Pl Laan 2, B-1050 Brussels, Belgium..
    Tiels, K.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology.
    Schoukens, J.
    Vrije Univ Brussel, Dept Engn Technol INDI, Pl Laan 2, B-1050 Brussels, Belgium.;Eindhoven Univ Technol TU E, Dept Elect Engn, Eindhoven, Netherlands..
    Runacres, M. C.
    Vrije Univ Brussel, Dept Engn Technol INDI, Pl Laan 2, B-1050 Brussels, Belgium.;Vrije Univ Brussel, Thermo & Fluid Dynam FLOW, Pl Laan 2, B-1050 Brussels, Belgium..
    A nonlinear model of vortex-induced forces on an oscillating cylinder in a fluid flow2020In: Journal of Fluids and Structures, ISSN 0889-9746, E-ISSN 1095-8622, Vol. 96, article id UNSP 103029Article in journal (Refereed)
    Abstract [en]

    A nonlinear model relating the imposed motion of a circular cylinder, submerged in a fluid flow, to the transverse force coefficient is presented. The nonlinear fluid system, featuring vortex shedding patterns, limit cycle oscillations and synchronisation, is studied both for swept sine and multisine excitation. A nonparametric nonlinear distortion analysis (FAST) is used to distinguish odd from even nonlinear behaviour. The information which is obtained from the nonlinear analysis is explicitly used in constructing a nonlinear model of the polynomial nonlinear state-space (PNLSS) type. The latter results in a reduction of the number of parameters and an increased accuracy compared to the generic modelling approach where typically no such information of the nonlinearity is used. The obtained model is able to accurately simulate time series of the transverse force coefficient over a wide range of the frequency-amplitude plane of imposed cylinder motion. (C) 2020 Elsevier Ltd. All rights reserved.

  • 46.
    Deglaire, Paul
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Analytical Aerodynamic Simulation Tools for Vertical Axis Wind Turbines2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wind power is a renewable energy source that is today the fastest growing solution to reduce CO2 emissions in the electric energy mix. Upwind horizontal axis wind turbine with three blades has been the preferred technical choice for more than two decades. This horizontal axis concept is today widely leading the market. The current PhD thesis will cover an alternative type of wind turbine with straight blades and rotating along the vertical axis. A brief overview of the main differences between the horizontal and vertical axis concept has been made. However the main focus of this thesis is the aerodynamics of the wind turbine blades.

    Making aerodynamically efficient turbines starts with efficient blades. Making efficient blades requires a good understanding of the physical phenomena and effective simulations tools to model them. The specific aerodynamics for straight bladed vertical axis turbine flow are reviewed together with the standard aerodynamic simulations tools that have been used in the past by blade and rotor designer. A reasonably fast (regarding computer power) and accurate (regarding comparison with experimental results) simulation method was still lacking in the field prior to the current work. This thesis aims at designing such a method.

    Analytical methods can be used to model complex flow if the geometry is simple. Therefore, a conformal mapping method is derived to transform any set of section into a set of standard circles. Then analytical procedures are generalized to simulate moving multibody sections in the complex vertical flows and forces experienced by the blades. Finally the fast semi analytical aerodynamic algorithm boosted by fast multipole methods to handle high number of vortices is coupled with a simple structural model of the rotor to investigate potential aeroelastic instabilities.

    Together with these advanced simulation tools, a standard double multiple streamtube model has been developed and used to design several straight bladed rotor ranging from 2 kW to 20 kW.

    List of papers
    1. Conformal mapping and efficient boundary element method without, boundary elements for fast vortex particle simulations
    Open this publication in new window or tab >>Conformal mapping and efficient boundary element method without, boundary elements for fast vortex particle simulations
    2008 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 27, no 2, p. 150-176Article in journal (Refereed) Published
    Abstract [en]

    In this paper, a revitalization of conformal mapping methods applied to fluid flows in two dimensions is proposed. The present work addresses several important issues concerning their application for vortex particle flow solvers. Difficulties of past conformal based method are reviewed. One difficulty concerns the ability of a mapping procedure to represent complicated shapes. The present paper improves past algorithms to be able to map new shapes, including multiply connected domains. A new fast procedure allows transferring a set of points in the mapped simplified plane to the complicated domain and vice versa. After a mapping construction, it is demonstrated how basic exact solutions to potential flow problems with vortices can be put in a new form which provides a faster and more accurate computation than with distributed singularity methods.

    Keywords
    conformal mapping, Laurent's series expansion, fast imaging
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-110478 (URN)10.1016/j.euromechflu.2007.03.005 (DOI)000254116800005 ()
    Available from: 2009-11-16 Created: 2009-11-16 Last updated: 2017-12-12Bibliographically approved
    2. Analytical solutions for a single blade in vertical axis turbine motion in two dimensions
    Open this publication in new window or tab >>Analytical solutions for a single blade in vertical axis turbine motion in two dimensions
    2009 (English)In: European journal of mechanics. B, Fluids, ISSN 0997-7546, E-ISSN 1873-7390, Vol. 28, p. 506-520Article in journal (Refereed) Published
    National Category
    Computational Mathematics Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-88420 (URN)10.1016/j.euromechflu.2008.11.004 (DOI)000267179900004 ()
    Available from: 2009-02-01 Created: 2009-02-01 Last updated: 2018-11-12Bibliographically approved
    3. A Multi-Body Vortex Method Applied to Vertical Axis Wind Turbines
    Open this publication in new window or tab >>A Multi-Body Vortex Method Applied to Vertical Axis Wind Turbines
    2010 (English)Article in journal (Refereed) Accepted
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-131981 (URN)
    Available from: 2010-10-12 Created: 2010-10-12 Last updated: 2014-12-10Bibliographically approved
    4. Fast aeroelastic model for straight bladed vertical axis wind and hydro turbines
    Open this publication in new window or tab >>Fast aeroelastic model for straight bladed vertical axis wind and hydro turbines
    2010 (English)In: Wind Engineering, ISSN 0309-524XArticle in journal (Refereed) Accepted
    Place, publisher, year, edition, pages
    Multi Science Publishing, 2010
    National Category
    Engineering and Technology
    Research subject
    Engineering Science with specialization in Science of Electricity
    Identifiers
    urn:nbn:se:uu:diva-131987 (URN)
    Available from: 2010-10-12 Created: 2010-10-12 Last updated: 2014-12-10Bibliographically approved
    5. Matching a permanent magnet synchronous generator to a fixed pitch vertical axis turbine for marine current energy conversion
    Open this publication in new window or tab >>Matching a permanent magnet synchronous generator to a fixed pitch vertical axis turbine for marine current energy conversion
    Show others...
    2009 (English)In: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691, Vol. 34, no 1, p. 24-31Article in journal (Refereed) Published
    Abstract [en]

    Extracting energy from a free-flow marine current using a vertical axis fixed pitch turbine requires a generator that can handle varying speeds and loads, since such a turbine gives maximum power capture for a fixed tip speed ratio. A prototype of such a generator has been designed and constructed. In this paper, its variable speed and load operation is evaluated, both in terms of how the constructed generator performs in relation to simulations, and in terms of how the generator could perform with three different fixed pitch turbines. Measurements of root mean square (RMS) voltage and current differ 10% from simulations. Performance analysis with example turbines shows that the generator can match fixed tip speed ratio operation of several turbines for current speeds between 0.5 and 2.5 m/s.

    Keywords
    Fixed tip speed ratio operation, permanent magnet generators, tidal power generation, variable speed generator, vertical axis turbine
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-96617 (URN)10.1109/JOE.2008.2010658 (DOI)000264618000003 ()
    Available from: 2008-01-11 Created: 2008-01-11 Last updated: 2022-01-28Bibliographically approved
    6. Design of a 12kW vertical axis wind turbine equipped with a direct driven PM synchronous generator
    Open this publication in new window or tab >>Design of a 12kW vertical axis wind turbine equipped with a direct driven PM synchronous generator
    Show others...
    2006 (English)In: EWEC 2006 - European Wind Energy Conference & Exhibition, Athens, GreeceArticle in journal (Refereed) Published
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97452 (URN)
    Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2016-07-12Bibliographically approved
    7. Experimental results from a 12 kW vertical axis wind turbine with a direct driven PM synchronous generator
    Open this publication in new window or tab >>Experimental results from a 12 kW vertical axis wind turbine with a direct driven PM synchronous generator
    2007 (English)Conference paper, Published paper (Other academic)
    Abstract [en]

    Experimental results from a three bladed vertical axis wind turbine with a direct driven PM synchronous generatorare presented. The H-rotor turbine, independent of wind direction, does not require any yaw mechanism.Furthermore, the variable speed, stall regulated turbine does not require pitch mechanism. The specifically designeddirectly driven generator eliminates the need for a gearbox. All electrical equipment, including generator, are placedon the ground. This reduces the weight that has to be supported by the structure and simplifies maintenance. Thus, theoverall strength of this concept is simplicity.The H-rotor has five meter long blades that are tapered at the tips. The aerodynamic torque is transferred to thegenerator via a 5.4 meter long drive shaft supported by a tower. A universal joint connects the drive shaft to thegenerator shaft, cancelling any transverse bending moments from the turbine on the generator. The generator acts as amotor to start up the turbine using a separate auxiliary winding. The turbine has a swept area of 30 m2 and is rated at12 kW in 12 m/s winds for 127 rpm.The turbine has been placed on a site where the wind resources have been extensively documented. The wind datarecord is more then ten years and includes data from various heights giving an accurate wind mapping of the area.The experimental aerodynamic power curve in turbulent wind conditions is presented. Considering the highlyturbulent wind conditions and the small size of the wind turbine these results are encouraging.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97453 (URN)
    Conference
    EWEC 2007 - European Wind Energy Conference & Exhibition, Milan, Italy, May. 7-10, 2007
    Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2018-05-30Bibliographically approved
    8. Progress of control system and measurement techniques for a 12 kW vertical axis wind turbine
    Open this publication in new window or tab >>Progress of control system and measurement techniques for a 12 kW vertical axis wind turbine
    Show others...
    2008 (English)Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:uu:diva-97454 (URN)
    Conference
    ??
    Available from: 2008-09-05 Created: 2008-09-05 Last updated: 2022-01-28Bibliographically approved
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    INSIDE02
  • 47.
    Dhangekar, Arshey
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering.
    Automatic data processing of traction motor measured data and vibration analysis of test bench2021Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    One of the goals of ABB AB is to develop highly efficient electric motors for traction application. The demand for traction motors is increasing due to the rise in electric vehicles sale and railway locomotive engines. Highly efficient traction motors will assist in reducing the pollution caused by fossil fuels and help make the earth a better place to live by leveraging sustainable energy.

    The electrical and mechanical characteristics of electric motors are measured and analyzed in the lab. The measured data of the electric motor in the lab are analyzed using the conventional way. One of the significant challenges in a conventional way is to isolate the system with various limitations, and it offers very few choices for measurement. The data management of measured observation readings is affected severely due to this, and it is then risky to determine and analyze the characteristics of electric motors.

    The first aim is to develop an automatic data processing algorithm for the measurement data collected from the specific setup of the electrical machine.

    The data processing is done using the MATLAB tool. Statistical methods such as mean, median, moving mean, moving median, Gaussian model for handling missing data, outliers, and data smoothing methods have been implemented to get accurately measured datasets as a part of this thesis.

    In addition, a study of vibrational analysis of the test bench assembly was performed for the traction motor. The natural frequency of test bench assembly is computed on the Finite Element Method (FEM) tool. All the natural frequencies of the test bench assembly with the traction motor are analyzed, and some of them were closed to the excitation frequency of the traction motor.  This study found that the resonance frequency of the test bench assembly has to be prevented while operating the traction motor during lab to strengthen the life of the test bench.

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  • 48.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Isberg, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Eriksson, Mikael
    Leijon, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Properties of the energy transport for plane-parallel polychromatic surface gravity waves in waters of arbitrary depthIn: IEEE Journal of Oceanic Engineering, ISSN 0364-9059, E-ISSN 1558-1691Article in journal (Other academic)
  • 49.
    Engström, Jens
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Shahroozi, Zahra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Katsidoniotaki, Eirini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS).
    Stavropoulou, Charitini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Johannesson, Pär
    RISE Research Institutes of Sweden, Department of Applied Mechanics.
    Göteman, Malin
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Centre of Natural Hazards and Disaster Science (CNDS).
    Offshore Measurements and Numerical Validation of the Mooring Forces on a 1:5 Scale Buoy2023In: Journal of Marine Science and Engineering, E-ISSN 2077-1312, Vol. 11, no 1, article id 231Article in journal (Refereed)
    Abstract [en]

    Wave energy conversion is a renewable energy technology with a promising potential. Although it has been developed for more than 200 years, the technology is still far from mature. The survivability in extreme weather conditions is a key parameter halting its development. We present here results from two weeks of measurement with a force measurement buoy deployed at Uppsala University’s test site for wave energy research at the west coast of Sweden. The collected data have been used to investigate the reliability for two typical numerical wave energy converter models: one low fidelity model based on linear wave theory and one high fidelity Reynolds-Averaged Navier–Stokes model. The line force data is also analysed by extreme value theory using the peak-over-threshold method to study the statistical distribution of extreme forces and to predict the return period. The high fidelity model shows rather good agreement for the smaller waves, but overestimates the forces for larger waves, which can be attributed to uncertainties related to field measurements and numerical modelling uncertainties. The peak-over-threshold method gives a rather satisfying result for this data set. A significant deviation is observed in the measured force for sea states with the same significant wave height. This indicates that it will be difficult to calculate the force based on the significant wave height only, which points out the importance of more offshore experiments.

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  • 50.
    Fornell, Anna
    et al.
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology. Lund Univ, MAX Lab 4, S-22484 Lund, Sweden.
    Baasch, Thierry
    Lund Univ, Dept Biomed Engn, S-22100 Lund, Sweden.
    Johannesson, Carl
    Lund Univ, Dept Biomed Engn, S-22100 Lund, Sweden.
    Nilsson, Johan
    Lund Univ, Dept Biomed Engn, S-22100 Lund, Sweden.
    Tenje, Maria
    Uppsala University, Science for Life Laboratory, SciLifeLab. Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Materials Science and Engineering, Microsystems Technology.
    Binary acoustic trapping in a glass capillary2021In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 54, no 35, article id 355401Article in journal (Refereed)
    Abstract [en]

    Acoustic trapping is a useful method for handling biological samples in microfluidic systems. The aim of this work is twofold: first to investigate the physics behind acoustic trapping in a glass capillary and secondly to perform binary acoustic trapping. The latter is achieved by increasing the density of the fluid in the trapping channel. The trapping device consisted of a glass capillary with a rectangular inner cross-section (height 200 µm × width 2000 µm) equipped with a small piezoelectric transducer. The piezoelectric transducer was actuated at 4 MHz to generate a localised half-wavelength acoustic standing-wave-field in the capillary, comprising of a pressure field and a velocity field. Under acoustic actuation, only particles with higher density than the fluid, i.e. having a positive dipole scattering coefficient, were trapped in the flow direction. The numerical and analytical modelling of the system show that the trapping force which retains the particles against the flow depends only on the dipole scattering coefficient in the pressure nodal plane of the acoustic field. The analytical model also reveals that the retention force is proportional to the dipole scattering coefficient, which agrees with our experimental findings. Next, we showed that in a mixture of melamine particles and polystyrene particles in a high-density fluid it is possible to selectively trap melamine particles, since melamine particles have higher density than polystyrene particles.

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