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  • 1.
    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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  • 2.
    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)
  • 3.
    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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    FULLTEXT01
  • 4. 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)
  • 5.
    Forslund, Johan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mendoza, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Impact of Blade Pitch Angle on Turbine Performance of a Vertical Axis Current TurbineManuscript (preprint) (Other academic)
  • 6.
    Mendoza, Victor
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Aerodynamic Studies of Vertical Axis Wind Turbines using the Actuator Line Model2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis addresses the unsteady aerodynamics involved in the operation of vertical axis wind turbines (VAWTs). The main focus is to represent and understand the most relevant phenomena within the resulting flow pattern as the wake structure, loads on the different turbine components and the performance of the rotor. An actuator line model has been used for this purpose.

    This model has been validated against experimental measurements from diverse cases with different operating conditions in both confined wind tunnels and open site locations. Numerical works were carried out considering a wide range of tip speed ratios (TSRs), and therefore covering from the no stall to the deep stall regime. The latter requires the implementation of a dynamic stall model for the proper representation of the unsteady forces on the blades. Also, different inlet conditions such as a uniform flow, a logarithmic wind shear and an atmospheric boundary layer (ABL) have been tested. The so-called recycling method technique was used to produce the fully developed ABL flow. Additionally, the resulting wake and performance of interacting turbines has been studied.

    Once the model was validated, two numerical study cases for large scale turbines were carried out. First, the performance and resulting flow field from both a horizontal axis wind turbine (HAWT) and VAWT were investigated when the turbines were operating at their optimal TSR and within the same ABL inflow boundary conditions. The influence of the variation on the atmospheric turbulence levels was also studied, as well as the differences and similarities on the obtained results for both type of turbines. Later, the performance improvement of two interacting VAWTs was investigated through the deflected wake produced by the pitched struts of the upstream turbine. This is presented as a novel mechanism to mitigate losses on interacting turbine arrangements (i.e. wind farms).

    In general, there is a reasonable good agreement between numerical results and experimental measurements, and therefore, the applied ALM can be considered as a potential tool for VAWTs simulations, characterized by relatively low computational cost showing accuracy and numerical stability.

    List of papers
    1. Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines
    Open this publication in new window or tab >>Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines
    2016 (English)In: Science Of Making Torque From Wind (Torque 2016) / [ed] IOP, 2016, article id 022043Conference paper, Published paper (Refereed)
    Abstract [en]

    Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicular to the rotor axis are some of the most important advantages over conventional horizontal axis wind turbines (HAWT). However, VAWT encounter complex and unsteady fluid dynamics, which present significant modeling challenges. One of the most relevant phenomena is dynamic stall, which is caused by the unsteady variation of angle of attack throughout the blade rotation, and is the focus of the present study. Dynamic stall is usually used as a passive control for VAWT operating conditions, hence the importance of predicting its effects. In this study, a coupled model is implemented with the open-source CFD toolbox OpenFOAM for solving the Navier-Stokes equations, where an actuator line model and dynamic stall model are used to compute the blade loading and body force. Force coefficients obtained from the model are validated with experimental data of pitching airfoil in similar operating conditions as an H-rotor type VAWT. Numerical results show reasonable agreement with experimental data for pitching motion.

    Series
    Journal of Physics Conference Series, ISSN 1742-6588, E-ISSN 1742-6596 ; 753
    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-305170 (URN)10.1088/1742-6596/753/2/022043 (DOI)000436325700043 ()
    Conference
    The Science of Making Torque from Wind (TORQUE 2016),OCT 05-07, 2016, Munich, Germany
    Funder
    StandUp for Wind
    Available from: 2016-10-12 Created: 2016-10-12 Last updated: 2020-01-07Bibliographically approved
    2. Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear
    Open this publication in new window or tab >>Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear
    2017 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 854, article id 012031Article in journal (Refereed) Published
    Abstract [en]

    The current trend of the wind energy industry aims for large scale turbines installed in wind farms. This brings a renewed interest in vertical axis wind turbines (VAWTs) since they have several advantages over the traditional Horizontal Axis Wind Tubines (HAWTs) for mitigating the new challenges. However, operating VAWTs are characterized by complex aerodynamics phenomena, presenting considerable challenges for modeling tools. An accurate and reliable simulation tool for predicting the interaction between the obtained wake of an operating VAWT and the flow in atmospheric open sites is fundamental for optimizing the design and location of wind energy facility projects. The present work studies the wake produced by a VAWT and how it is affected by the surface roughness of the terrain, without considering the effects of the ambient turbulence intensity. This study was carried out using an actuator line model (ALM), and it was implemented using the open-source CFD library OpenFOAM to solve the governing equations and to compute the resulting flow fields. An operational H-shaped VAWT model was tested, for which experimental activity has been performed at an open site north of Uppsala-Sweden. Different terrains with similar inflow velocities have been evaluated. Simulated velocity and vorticity of representative sections have been analyzed. Numerical results were validated using normal forces measurements, showing reasonable agreement.

    National Category
    Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-348342 (URN)10.1088/1742-6596/854/1/012031 (DOI)000435276400031 ()
    Conference
    Wake Conference, MAY 30-JUN 01, 2017, Uppsala Univ Gotland Campus, Visby, SWEDEN
    Funder
    StandUp for Wind
    Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-11-23Bibliographically approved
    3. Near-Wake Flow Simulation of a Vertical Axis Turbine Using an Actuator Line Model
    Open this publication in new window or tab >>Near-Wake Flow Simulation of a Vertical Axis Turbine Using an Actuator Line Model
    2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 2, p. 171-188Article in journal (Refereed) Published
    Abstract [en]

    In the present work, the near‐wake generated for a vertical axis wind turbine (VAWT) was simulated using an actuator line model (ALM) in order to validate and evaluate its accuracy. The sensitivity of the model to the variation of the spatial and temporal discretization was studied and showed a bigger response to the variation in the mesh size as compared with the temporal discretization. The large eddy simulation (LES) approach was used to predict the turbulence effects. The performance of Smagorinsky, dynamic k‐equation, and dynamic Lagrangian turbulence models was tested, showing very little relevant differences between them. Generally, predicted results agree well with experimental data for velocity and vorticity fields in representative sections. The presented ALM was able to characterize the main phenomena involved in the flow pattern using a relatively low computational cost without stability concerns, identified the general wake structure (qualitatively and quantitatively), and the contribution from the blade tips and motion on it. Additionally, the effects of the tower and struts were investigated with respect to the overall structure of the wake, showing no significant modification. Similarities and discrepancies between numerical and experimental results are discussed. The obtained results from the various simulations carried out here can be used as a practical reference guideline for choosing parameters in VAWTs simulations using the ALM.

    Keywords
    actuator line model, dynamic stall model, near wake simulation, vawt, vertical axis wind turbine
    National Category
    Energy Engineering Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-348688 (URN)10.1002/we.2277 (DOI)000455955800002 ()
    Funder
    StandUp for Wind
    Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-02-05Bibliographically approved
    4. Validation of Actuator Line and Vortex Models using Normal Forces Measurements of a Straight-Bladed Vertical Axis Wind Turbine
    Open this publication in new window or tab >>Validation of Actuator Line and Vortex Models using Normal Forces Measurements of a Straight-Bladed Vertical Axis Wind Turbine
    2020 (English)In: Energies, E-ISSN 1996-1073, Vol. 13, no 3, article id 511Article in journal (Refereed) Published
    Abstract [en]

    Vertical Axis Wind Turbines (VAWTs) are characterized by complex and unsteady flow patterns resulting in considerable challenges for both numerical simulations and measurements describing the phenomena involved. In this study, a 3D Actuator Line Model (ALM) is compared to a 2D and a 3D Vortex Model, and they are validated using the normal forces measurements on a blade of an operating 12 kW VAWT, which is located in an open site in the north of Uppsala, Sweden. First, the coefficient power ( Cp ) curve of the device has been simulated and compared against the experimental one. Then, a wide range of operational conditions for different tip speed ratios (TSRs), with λ = 1.84, 2.55, 3.06, 3.44, 4.09 and 4.57 were investigated. The results showed descent agreement with the experimental data for both models in terms of the trend and magnitudes. On one side, a slight improvement for representing the normal forces was achieved by the ALM, while the vortex code performs better in the simulation of the Cp curve. Similarities and discrepancies between numerical and experimental results are discussed.

    Keywords
    vertical axis wind turbines, actuator line model, vortex method, dynamic stall model
    National Category
    Other Environmental Engineering
    Identifiers
    urn:nbn:se:uu:diva-348689 (URN)10.3390/en13030511 (DOI)000522489000005 ()
    Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2023-08-28Bibliographically approved
    5. Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions
    Open this publication in new window or tab >>Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions
    2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 458-472Article in journal (Refereed) Published
    Abstract [en]

    A numerical study of both a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT) with similar size and power rating is presented. These large scale turbines have been tested when operating stand-alone at their optimal tip speed ratio (TSR) within a neutrally stratified atmospheric boundary layer (ABL). The impact of three different surface roughness lengths on the turbine performance is studied for the both turbines. The turbines performance, the response to the variation in the surface roughness of terrain, and the most relevant phenomena involved on the resulting wake were investigated. The main goal was to evaluate the differences and similarities of these two different types of turbine when they operate under the same atmospheric flow conditions. An actuator line model (ALM) was used together with the large eddy simulation (LES) approach for predicting wake effects, and it was implemented using the open-source computational fluid dynamics (CFD) library OpenFOAM to solve the governing equations and to compute the resulting flow fields. This model was first validated using wind tunnel measurements of power coefficients and wake of interacting HAWTs, and then employed to study the wake structure of both full scale turbines. A preliminary study test comparing the forces on a VAWT blades against measurements was also investigated. These obtained results showed a better performance and shorter wake (faster recovery) for an HAWT compared with a VAWT for the same atmospheric conditions.

    National Category
    Fluid Mechanics and Acoustics Energy Engineering
    Identifiers
    urn:nbn:se:uu:diva-348690 (URN)10.1002/we.2299 (DOI)000461904600002 ()
    Funder
    StandUp for Wind
    Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-05-07Bibliographically approved
    6. Improving farm efficiency of interacting vertical‐axis wind turbines through wake deflection using pitched struts
    Open this publication in new window or tab >>Improving farm efficiency of interacting vertical‐axis wind turbines through wake deflection using pitched struts
    2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 538-546Article in journal (Refereed) Published
    Abstract [en]

    This work presents a numerical study of the obtained performance and the resulting flow field between two interacting large scale vertical-axis wind turbines (VAWTs), under the influence of a deflected wake through the struts pitching of the upwind turbine. The configuration consists of two VAWTs aligned in the direction of the incoming flow in which a wide range of fixed struts pitching angles in the upwind turbine have been investigated. The main goal is to evaluate the influence of the wake deflection on the turbines performance while they are operating at their optimal tip speed ratio (TSR), and to reproduce the most relevant phenomena involved in the flow pattern of the interacting wake. Arrangements with cross-stream offsets have also been tested for quantifying the contribution of this modification into the overall performance. For this purpose, an actuator line model (ALM) has been implemented using the open-source CFD library OpenFOAM in order to solve the governing equations and to calculate the resulting flow. The Large eddy simulation (LES) approach is considered to reproduce the turbulence flow effects. A preliminary study to identify the optimal TSR of the interacting downwind turbine has been investigated.

    Keywords
    actuator line model (ALM), dynamic stall model (DSM), large eddy simulation (LES), vertical axis wind turbines (VAWTs), wake deflection
    National Category
    Energy Engineering Fluid Mechanics and Acoustics
    Identifiers
    urn:nbn:se:uu:diva-348692 (URN)10.1002/we.2305 (DOI)000461904600008 ()
    Funder
    StandUp for Wind
    Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-05-07Bibliographically approved
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  • 7.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bachant, Peter
    WindESCo Inc, Boston, MA USA.
    Ferreira, Carlos
    Delft Univ Technol, Wind Energy Res Inst, TU Delft, Delft, Netherlands.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Near-Wake Flow Simulation of a Vertical Axis Turbine Using an Actuator Line Model2019In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 2, p. 171-188Article in journal (Refereed)
    Abstract [en]

    In the present work, the near‐wake generated for a vertical axis wind turbine (VAWT) was simulated using an actuator line model (ALM) in order to validate and evaluate its accuracy. The sensitivity of the model to the variation of the spatial and temporal discretization was studied and showed a bigger response to the variation in the mesh size as compared with the temporal discretization. The large eddy simulation (LES) approach was used to predict the turbulence effects. The performance of Smagorinsky, dynamic k‐equation, and dynamic Lagrangian turbulence models was tested, showing very little relevant differences between them. Generally, predicted results agree well with experimental data for velocity and vorticity fields in representative sections. The presented ALM was able to characterize the main phenomena involved in the flow pattern using a relatively low computational cost without stability concerns, identified the general wake structure (qualitatively and quantitatively), and the contribution from the blade tips and motion on it. Additionally, the effects of the tower and struts were investigated with respect to the overall structure of the wake, showing no significant modification. Similarities and discrepancies between numerical and experimental results are discussed. The obtained results from the various simulations carried out here can be used as a practical reference guideline for choosing parameters in VAWTs simulations using the ALM.

  • 8.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Bachant, Peter
    Center for Ocean Renewable Energy, University of New Hampshire, 24 Colovos Rd., Durham, NH 03824, USA.
    Wosnik, Martin
    Center for Ocean Renewable Energy, University of New Hampshire, 24 Colovos Rd., Durham, NH 03824, USA.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines2016In: Science Of Making Torque From Wind (Torque 2016) / [ed] IOP, 2016, article id 022043Conference paper (Refereed)
    Abstract [en]

    Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicular to the rotor axis are some of the most important advantages over conventional horizontal axis wind turbines (HAWT). However, VAWT encounter complex and unsteady fluid dynamics, which present significant modeling challenges. One of the most relevant phenomena is dynamic stall, which is caused by the unsteady variation of angle of attack throughout the blade rotation, and is the focus of the present study. Dynamic stall is usually used as a passive control for VAWT operating conditions, hence the importance of predicting its effects. In this study, a coupled model is implemented with the open-source CFD toolbox OpenFOAM for solving the Navier-Stokes equations, where an actuator line model and dynamic stall model are used to compute the blade loading and body force. Force coefficients obtained from the model are validated with experimental data of pitching airfoil in similar operating conditions as an H-rotor type VAWT. Numerical results show reasonable agreement with experimental data for pitching motion.

    Download full text (pdf)
    fulltext
  • 9.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Chaudhari, Ashvinkumar
    Lappeenranta Univ Technol, Sch Engn Sci, CEID, Lappeenranta, Finland.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions2019In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 458-472Article in journal (Refereed)
    Abstract [en]

    A numerical study of both a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT) with similar size and power rating is presented. These large scale turbines have been tested when operating stand-alone at their optimal tip speed ratio (TSR) within a neutrally stratified atmospheric boundary layer (ABL). The impact of three different surface roughness lengths on the turbine performance is studied for the both turbines. The turbines performance, the response to the variation in the surface roughness of terrain, and the most relevant phenomena involved on the resulting wake were investigated. The main goal was to evaluate the differences and similarities of these two different types of turbine when they operate under the same atmospheric flow conditions. An actuator line model (ALM) was used together with the large eddy simulation (LES) approach for predicting wake effects, and it was implemented using the open-source computational fluid dynamics (CFD) library OpenFOAM to solve the governing equations and to compute the resulting flow fields. This model was first validated using wind tunnel measurements of power coefficients and wake of interacting HAWTs, and then employed to study the wake structure of both full scale turbines. A preliminary study test comparing the forces on a VAWT blades against measurements was also investigated. These obtained results showed a better performance and shorter wake (faster recovery) for an HAWT compared with a VAWT for the same atmospheric conditions.

  • 10.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Improving farm efficiency of interacting vertical‐axis wind turbines through wake deflection using pitched struts2019In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 538-546Article in journal (Refereed)
    Abstract [en]

    This work presents a numerical study of the obtained performance and the resulting flow field between two interacting large scale vertical-axis wind turbines (VAWTs), under the influence of a deflected wake through the struts pitching of the upwind turbine. The configuration consists of two VAWTs aligned in the direction of the incoming flow in which a wide range of fixed struts pitching angles in the upwind turbine have been investigated. The main goal is to evaluate the influence of the wake deflection on the turbines performance while they are operating at their optimal tip speed ratio (TSR), and to reproduce the most relevant phenomena involved in the flow pattern of the interacting wake. Arrangements with cross-stream offsets have also been tested for quantifying the contribution of this modification into the overall performance. For this purpose, an actuator line model (ALM) has been implemented using the open-source CFD library OpenFOAM in order to solve the governing equations and to calculate the resulting flow. The Large eddy simulation (LES) approach is considered to reproduce the turbulence flow effects. A preliminary study to identify the optimal TSR of the interacting downwind turbine has been investigated.

  • 11.
    Mendoza, Victor
    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.
    Validation of Actuator Line and Vortex Models using Normal Forces Measurements of a Straight-Bladed Vertical Axis Wind Turbine2020In: Energies, E-ISSN 1996-1073, Vol. 13, no 3, article id 511Article in journal (Refereed)
    Abstract [en]

    Vertical Axis Wind Turbines (VAWTs) are characterized by complex and unsteady flow patterns resulting in considerable challenges for both numerical simulations and measurements describing the phenomena involved. In this study, a 3D Actuator Line Model (ALM) is compared to a 2D and a 3D Vortex Model, and they are validated using the normal forces measurements on a blade of an operating 12 kW VAWT, which is located in an open site in the north of Uppsala, Sweden. First, the coefficient power ( Cp ) curve of the device has been simulated and compared against the experimental one. Then, a wide range of operational conditions for different tip speed ratios (TSRs), with λ = 1.84, 2.55, 3.06, 3.44, 4.09 and 4.57 were investigated. The results showed descent agreement with the experimental data for both models in terms of the trend and magnitudes. On one side, a slight improvement for representing the normal forces was achieved by the ALM, while the vortex code performs better in the simulation of the Cp curve. Similarities and discrepancies between numerical and experimental results are discussed.

    Download full text (pdf)
    fulltext
  • 12.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines2016Conference paper (Refereed)
    Download full text (pdf)
    fulltext
  • 13.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Goude, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear2017In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 854, article id 012031Article in journal (Refereed)
    Abstract [en]

    The current trend of the wind energy industry aims for large scale turbines installed in wind farms. This brings a renewed interest in vertical axis wind turbines (VAWTs) since they have several advantages over the traditional Horizontal Axis Wind Tubines (HAWTs) for mitigating the new challenges. However, operating VAWTs are characterized by complex aerodynamics phenomena, presenting considerable challenges for modeling tools. An accurate and reliable simulation tool for predicting the interaction between the obtained wake of an operating VAWT and the flow in atmospheric open sites is fundamental for optimizing the design and location of wind energy facility projects. The present work studies the wake produced by a VAWT and how it is affected by the surface roughness of the terrain, without considering the effects of the ambient turbulence intensity. This study was carried out using an actuator line model (ALM), and it was implemented using the open-source CFD library OpenFOAM to solve the governing equations and to compute the resulting flow fields. An operational H-shaped VAWT model was tested, for which experimental activity has been performed at an open site north of Uppsala-Sweden. Different terrains with similar inflow velocities have been evaluated. Simulated velocity and vorticity of representative sections have been analyzed. Numerical results were validated using normal forces measurements, showing reasonable agreement.

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  • 14.
    Mendoza, Victor
    et al.
    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.
    Bernhoff, Hans
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity.
    Numerical Study of a Novel Concept for Manufacturing Savonius Turbines with Twisted Blades2020In: Energies, E-ISSN 1996-1073, Vol. 13, no 8, article id 1874Article in journal (Refereed)
    Abstract [en]

    This work presents a numerical study of the aerodynamic performance and the resulting flow field of two novel Savonius wind turbines with twisted blades. The novelty relies on the blade manufacturing process which is characterized by a 'twisted cut' through the central axis of a hollow cylinder (tube), followed by a partial twisted cut in the range of 90 degrees. This approach does not require any expensive fabrication process such as blade molding and/or 3D prints, and, therefore, it can potentially mitigate the production costs. The main goal is to investigate the operational parameters and the overall performance of the presented devices, which are currently being operated in atmospheric conditions. For this purpose, three-dimensional simulations have been performed using the open-source CFD library OpenFOAM in order to solve the governing equations and for characterizing the main phenomena involved in the flow pattern. The Reynolds-averaged Navier-Stokes (RANS) approach together with the k-omega SST model were employed to reproduce the flow turbulence effects. This model is validated using wind tunnel measurements of the power (CP) and torque (CM) coefficients from a straight blade Savonius turbine. Unsteady simulations of the two turbine prototypes were investigated at different tip speed ratio TSR (lambda) by varying the rotational speed of the rotor while keeping constant the free stream (rated) velocity V infinity. The results were compared against the Savonius turbine employed for validating the model. Aerodynamic loads and general wake structure were studied at the optimal operational conditions as well. For the same turbine configurations, the new blade geometry improved the performance by 20-25% (at its optimal TSR), compared to the conventional straight blade Savonius rotor, as well as the reducing torque fluctuation.

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  • 15.
    Mendoza, Victor
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Hexicon AB, Stockholm, Sweden.;Hexicon AB, OstraJarnvagsgatan 27, S-11120 Stockholm, Sweden..
    Katsidoniotaki, Eirini
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Electrical Engineering, Electricity. Ctr Nat Hazards & Disaster Sci CNDS, Uppsala, Sweden..
    Florentiades, Markos
    Hexicon AB, Stockholm, Sweden..
    Fraga, Jorge Dot
    Hexicon AB, Stockholm, Sweden..
    Dyachuk, Eduard
    Hexicon AB, Stockholm, Sweden..
    Aerodynamic performance of a dual turbine concept characterized by a relatively close distance between rotors2023In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 26, no 6, p. 521-537Article in journal (Refereed)
    Abstract [en]

    In this work, a closely spaced dual turbine concept is studied. The distance between the two side-by-side hubs is 1.05D$$ D $$, where D$$ D $$ is the rotor diameter. This configuration has a potential benefit for offshore wind developments in which power density can be maximized. The main goal is to evaluate the overall aerodynamic performance, blade loads, and wake structure of a reference wind turbine generator operating within this dual turbine configuration and to compare the effects against those for the typical single turbine configuration. For this purpose, an actuator line model has been employed together with the large eddy simulation approach for predicting the turbulence effects. This model was implemented by using the open-source computational fluid dynamics toolbox OpenFOAM. Results show a better performance for the dual turbine concept. Under same operating conditions, the aerodynamic power of each turbine within the dual concept is higher than the power of the stand alone turbine, particularly at lower operating wind speeds (approximately 2% to 3% of extra power per turbine). Comparison between the two configurations shows similar character of the tangential and normal forces acting on the blades in terms of magnitude and fluctuation, eliminating potential concerns regarding fatigue and blade design. The largest difference in the tangential and normal root bending moments are approximately 3% and 2%, respectively, between single and dual turbine configurations. Finally, wake recovery analysis shows a downwind velocity deficit that is not enhanced streamwise in the dual turbine configuration with no considerable difference after 7D$$ D $$.

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