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Measurements of the Aerodynamic Normal Forces on a 12-kW Straight-Bladed Vertical Axis Wind Turbine
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2015 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 8, no 8Article in journal (Refereed) Published
Abstract [en]

The knowledge of unsteady forces is necessary when designing vertical axis wind turbines (VAWTs). Measurement data for turbines operating at an open site are still very limited. The data obtained from wind tunnels or towing tanks can be used, but have limited applicability when designing large-scale VAWTs. This study presents experimental data on the normal forces of a 12-kW straight-bladed VAWT operated at an open site north of Uppsala, Sweden. The normal forces are measured with four single-axis load cells. The data are obtained for a wide range of tip speed ratios: from 1.7 to 4.6. The behavior of the normal forces is analyzed. The presented data can be used in validations of aerodynamic models and the mechanical design for VAWTs.

Place, publisher, year, edition, pages
2015. Vol. 8, no 8
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-260569DOI: 10.3390/en8088482ISI: 000360586600052OAI: oai:DiVA.org:uu-260569DiVA: diva2:847662
Available from: 2015-08-20 Created: 2015-08-20 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Aerodynamics of Vertical Axis Wind Turbines: Development of Simulation Tools and Experiments
Open this publication in new window or tab >>Aerodynamics of Vertical Axis Wind Turbines: Development of Simulation Tools and Experiments
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis combines measurements with the development of simulation tools for vertical axis wind turbines (VAWT). Numerical models of aerodynamic blade forces are developed and validated against experiments. The studies were made on VAWTs which were operated at open sites. Significant progress within the modeling of aerodynamics of VAWTs has been achieved by the development of new simulation tools and by conducting experimental studies.        

An existing dynamic stall model was investigated and further modified for the conditions of the VAWT operation. This model was coupled with a streamtube model and assessed against blade force measurements from a VAWT with curved blades, operated by Sandia National Laboratories. The comparison has shown that the accuracy of the streamtube model has been improved compared to its previous versions. The dynamic stall model was further modified by coupling it with a free vortex model. The new model has become less dependent on empirical constants and has shown an improved accuracy.    

Unique blade force measurements on a 12 kW VAWT were conducted. The turbine was operated north of Uppsala. Load cells were used to measure the forces on the turbine. A comprehensive analysis of the measurement accuracy has been performed and the major error sources have been identified.

The measured aerodynamic normal force has been presented and analyzed for a wide range of operational conditions including dynamic stall, nominal operation and the region of high flow expansion. The improved vortex model has been validated against the data from the new measurements. The model agrees quite well with the experiments for the regions of nominal operation and high flow expansion. Although it does not reproduce all measurements in great detail, it is suggested that the presented vortex model can be used for preliminary estimations of blade forces due to its high computational speed and reasonable accuracy.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 86 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1274
Keyword
wind power, vertical axis turbine, H-rotor, simulations, streamtube model, vortex model, dynamic stall, measurements, blade, force
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-260573 (URN)978-91-554-9307-3 (ISBN)
Public defence
2015-10-09, Polhemssalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2015-09-17 Created: 2015-08-20 Last updated: 2015-10-01
2. Blade force measurements and electrical torque ripple of a vertical axis wind turbine
Open this publication in new window or tab >>Blade force measurements and electrical torque ripple of a vertical axis wind turbine
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Wind power has become an attractive alternative for clean energy production. Horizontal axis turbines are increasing in power rating and are maturing as products. The cost of maintenance, noise levels and durability are possible concerns of the modern horizontal axis wind turbines. The vertical axis wind turbine project at Uppsala University addresses these issues among others. The concept removes the need for any yaw or pitch mechanism. Even the gearbox is excluded with the use of a directly driven multi-pole permanent magnet generator. Additionally, the generator and power electronics is placed at ground level. The project has resulted in several open site prototypes of which a 12kW and 200 kW turbine are still subject to active research.

One major disadvantage of vertical axis wind turbines are the oscillating forces acting on the turbine. The first part of this work presents a measurement system developed to capture the forces acting on a blade during operation of the 12 kW prototype. The systems performance and data output is presented and thorough error estimations has been performed.

In modern turbines it is common to have the generator power rectified into a DC-voltage, feeding an inverter connected to the grid. The rectifier is usually also an inverter allowing full control of the generator and the DC-link voltage. In the concept used on the 12 kW prototype, the electric power of the generator is instead passively rectified using diodes to produce the DC-voltage. Diodes are considered a cheap and robust solution for producing the DC-voltage. However, one drawback is the high current ripples produced. The current ripples lead to an electric torque ripple. This work studies how this electric torque ripple translates into a mechanical torque ripple on the turbine. A simulation model is developed and the results are compared with the force measurements on the 12 kW prototype.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2016
Series
UURIE / Uppsala University, Department of Engineering Sciences, ISSN 0349-8352 ; 346-16L
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-272342 (URN)
Presentation
2016-02-10, Å4101, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2016-01-13 Created: 2016-01-13 Last updated: 2016-01-13Bibliographically approved
3. Electromechanics of Vertical Axis Wind Turbines
Open this publication in new window or tab >>Electromechanics of Vertical Axis Wind Turbines
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Wind power is an established mean of clean energy production and the modern horizontal axis wind turbine has become a common sight. The need for maintenance is high and future wind turbines may need to be improved to enable more remote and offshore locations. Vertical axis wind turbines have possible benefits, such as higher reliability, less noise and lower centre of gravity. This thesis focuses on electromechanical interaction in the straight bladed Darrieus rotor (H-rotor) concept studied at Uppsala University.

One of the challenges with vertical axis technology is the oscillating aerodynamic forces. A force measurement setup has been implemented to capture the forces on a three-bladed 12 kW open site prototype. The normal force showed good agreement with simulations. An aerodynamic torque could be estimated from the system. The total electrical torque in the generator was determined from electrical measurements. Both torque estimations lacked the expected aerodynamic ripple at three times per revolution. The even torque detected is an important result and more studies are required to confirm and understand it.

The force measurement was also used to study the loads on the turbine in parked conditions. It was discovered that there is a strong dependence on wind direction and that there is a positive torque on the turbine at stand still. The results can assist to determine the best parking strategies for an H-rotor turbine.

The studied concept also features diode rectification of the voltage from the permanent magnet synchronous generator. Diodes are considered a cheap and robust solution for rectification at the drawback of inducing ripple in the torque and output voltage. The propagation of the torque ripple was measured on the prototype and studied with simulations and analytical expressions. One key conclusion was that the mechanical driveline of the turbine is an effective filter of the diode induced torque ripple.

A critical speed controller was implemented on the prototype. The controller was based on optimal torque control and according to the experiments and the simulations it was able to avoid a rotational speed span. Finally, the optimal torque control was evaluated for multiple turbines with diode rectification to a common DC-link. The setup can potentially reduce the overall complexity of wind farms. The simulations suggest that stability of the system can be obtained by controlling the DC-link load as a semi constant voltage.

The thesis is based on nine papers of which six are treated in the thesis summary.

 

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2017. 81 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1581
Keyword
Wind power, Diode rectification, Control, Measurement, Simulation, Electromechanical coupling, vindkraft, diodlikriktning, reglering, mätning, simulering
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Energy Systems
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-331844 (URN)978-91-513-0117-4 (ISBN)
Public defence
2017-12-08, Å2005, Ångström Laboratory, Lägerhyddsvägen 1, Uppsala, 09:15 (English)
Opponent
Supervisors
Funder
StandUpStandUp for Wind
Available from: 2017-11-14 Created: 2017-10-18 Last updated: 2017-11-14

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Dyachuk, EduardRossander, MorganGoude, AndersBernhoff, Hans

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