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Fluid Mechanics of Vertical Axis Turbines: Simulations and Model Development
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Two computationally fast fluid mechanical models for vertical axis turbines are the streamtube and the vortex model. The streamtube model is the fastest, allowing three-dimensional modeling of the turbine, but lacks a proper time-dependent description of the flow through the turbine. The vortex model used is two-dimensional, but gives a more complete time-dependent description of the flow. Effects of a velocity profile and the inclusion of struts have been investigated with the streamtube model. Simulations with an inhomogeneous velocity profile predict that the power coefficient of a vertical axis turbine is relatively insensitive to the velocity profile. For the struts, structural mechanic loads have been computed and the calculations show that if turbines are designed for high flow velocities, additional struts are required, reducing the efficiency for lower flow velocities.Turbines in channels and turbine arrays have been studied with the vortex model. The channel study shows that smaller channels give higher power coefficients and convergence is obtained in fewer time steps. Simulations on a turbine array were performed on five turbines in a row and in a zigzag configuration, where better performance is predicted for the row configuration. The row configuration was extended to ten turbines and it has been shown that the turbine spacing needs to be increased if the misalignment in flow direction is large.A control system for the turbine with only the rotational velocity as input has been studied using the vortex model coupled with an electrical model. According to simulations, this system can obtain power coefficients close to the theoretical peak values. This control system study has been extended to a turbine farm. Individual control of each turbine has been compared to a less costly control system where all turbines are connected to a mutual DC bus through passive rectifiers. The individual control performs best for aerodynamically independent turbines, but for aerodynamically coupled turbines, the results show that a mutual DC bus can be a viable option.Finally, an implementation of the fast multipole method has been made on a graphics processing unit (GPU) and the performance gain from this platform is demonstrated.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. , 111 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 998
Keyword [en]
Wind power, Marine current power, Vertical axis turbine, Wind farm, Channel flow, Simulations, Vortex model, Streamtube model, Control system, Graphics processing unit, CUDA, Fast multipole method
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-183794ISBN: 978-91-554-8539-9 (print)OAI: oai:DiVA.org:uu-183794DiVA: diva2:564033
Public defence
2012-12-14, Polhemssalen, Ångströmslaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2012-11-22 Created: 2012-11-01 Last updated: 2013-02-11
List of papers
1. A parameter study of the influence of struts on the performance of a vertical-axis marine current turbine.
Open this publication in new window or tab >>A parameter study of the influence of struts on the performance of a vertical-axis marine current turbine.
2009 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Uppsala, Sweden: , 2009
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113279 (URN)
Conference
EWTEC09,
Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2016-04-14Bibliographically approved
2. Influence of a Varying Vertical Velocity Profile on Turbine Efficiency for a Vertical Axis Marine Current Turbine,
Open this publication in new window or tab >>Influence of a Varying Vertical Velocity Profile on Turbine Efficiency for a Vertical Axis Marine Current Turbine,
2009 (English)Conference paper, Published paper (Refereed)
Place, publisher, year, edition, pages
Honolulu, Hawaii.: , 2009
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113278 (URN)
Conference
Offshore and Arctic Engineering (OMAE 2009)
Available from: 2010-01-26 Created: 2010-01-26 Last updated: 2016-04-14Bibliographically approved
3. Design of an experimental setup for hydro-kinetic energy conversion
Open this publication in new window or tab >>Design of an experimental setup for hydro-kinetic energy conversion
Show others...
2009 (English)In: International Journal on Hydropower & Dams, ISSN 1352-2523, Vol. 16, no 5, 112-116 p.Article in journal (Refereed) Published
Abstract [en]

A hydro-kinetic energy project has been underway in Sweden since 2000, and an in-stream prototype setup for experiments at a site in a Swedish river is now in progress. The system comprises a vertical axis turbine and a directly driven permanent magnet generator. Methods and choices used in designing the system are described here. The turbine and generator are evaluated based on measurements and CFD simulations of conditions at the site for the experimental setup.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-113145 (URN)1352-2523 (ISBN)
Available from: 2010-01-25 Created: 2010-01-25 Last updated: 2016-04-14Bibliographically approved
4. Simulations of a vertical axis turbine in a channel
Open this publication in new window or tab >>Simulations of a vertical axis turbine in a channel
2014 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 63, 477-485 p.Article in journal (Refereed) Published
Abstract [en]

The power coefficient of a turbine increases according to the predictions from streamtube theory for sites with a confined fluid flow. Here, a vertical axis turbine (optimized for free flow) has been simulated by a two-dimensional vortex method, both in a channel and in free flow. The first part of the study concerns the numerical parameters of channel simulations. It is found that for free flow and wide channels, a large number of revolutions is required for convergence (around 100 at the optimal tip speed ratio and increasing with higher tip speed ratio), while for smaller channels, the required number of revolutions decreases. The second part analyses changes in turbine performance by the channel boundaries. The turbine performance increases when the channel width is decreased, although the results are below the predictions from streamtube theory, and this difference increases with decreasing channel width. It is also observed that the optimal tip speed ratio increases with decreasing channel width. By increasing the chord, which decreases the optimal tip speed ratio, the power coefficient can be increased somewhat.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
Vertical axis turbine, Vortex method, Channel flow, Simulation, Current power
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-183737 (URN)10.1016/j.renene.2013.09.038 (DOI)000330488100054 ()
Available from: 2012-11-01 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved
5. Numerical Simulation of a Farm of Vertical Axis Marine Current Turbines
Open this publication in new window or tab >>Numerical Simulation of a Farm of Vertical Axis Marine Current Turbines
2010 (English)In: PROCEEDINGS OF THE ASME 29TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING 2010, VOL 3, 2010, 335-344 p.Conference paper, Published paper (Refereed)
Abstract [en]

For commercial applications of marine current turbines, it can be useful to build several turbines close to each other in a farm, similar to wind turbine parks. To create a good farm configuration, the turbines' mutual interaction needs to be studied. Here, to obtain detailed information, several turbines were simulated together using a 2D vortex method. To limit the computational cost, the vortex method was combined with known profile section data for the blades.

First, a single turbine was compared against two turbines in close proximity. The two turbines were tested both with equal and opposite rotational direction, and the two blade pitch angles 0 and 3 degrees were tested. For both a single turbine and the two turbine case, a 3 degree pitch angle gave higher power coefficients than 0 degrees. The differences between 3 and 0 degrees were more significant for the single turbine. In all cases, the two turbine system had higher power coefficient per turbine than the single turbine.

A five turbine park was simulated with three different combinations, one with all turbines on a row, and two with a zigzag pattern, where the difference was that the last simulation had larger turbines than the other two. For 0 degrees incident flow angle, the turbines on the row obtained the highest power coefficient, while the larger turbines in zigzag pattern obtained higher total power. The case with the turbines on the row was most insensitive to changes in flow direction, and for a 30 degree change, the row produced the highest total power as well. By locating the turbines inside a channel, all turbines obtained higher power coefficients, and the increase was largest for the large turbines, which blocked the channel to a larger extent.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-142501 (URN)000290556500042 ()978-0-7918-4911-8 (ISBN)
Conference
29th ASME International Conference on Ocean, Offshore and Arctic Engineering Shanghai, PEOPLES R CHINA, JUN 06-11, 2010 ASME, Ocean, Offshore, & Arctic Engn Div
Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2016-04-18Bibliographically approved
6. Influence of incoming flow direction on spacing between vertical axis marine current turbines placed in a row
Open this publication in new window or tab >>Influence of incoming flow direction on spacing between vertical axis marine current turbines placed in a row
2012 (English)In: Proceedings of the ASME 31th International Conference on Ocean, Offshore and Artic Engineering, vol. 7, 2012, 285-291 p.Conference paper, Published paper (Refereed)
Abstract [en]

From the commercial point of view it may be beneficial to installa set of marine current turbines forming a park, by analogy with windparks. Consequently, this motivates research on park configurations.An array of ten vertical axis marine current turbines is simulatedto study how the distance between the turbines affects the performanceof the park for different flow directions. The simulations are performedusing a two-dimensional vortex method. An array of identical turbinesis created, where all turbines are on a single line. The turbinesare operated at the tip speed ratio, which corresponds to the highestpower coefficient for a single turbine. The distance between the turbinesis varied and the total power from the array is compared to the turbinespacing for different flow directions.Additionally, flow data from a real site is used to find an optimalorientation of the line of turbines. The performance of the arrayis estimated for the site as a function of turbine spacing.

National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-183733 (URN)10.1115/OMAE2012-83347 (DOI)000324507000035 ()978-0-7918-4494-6 (ISBN)
Conference
31st ASME International Conference on Ocean, Offshore and Arctic Engineering, Jul 01-06, 2012, Rio de Janeiro, Brazil
Funder
StandUpStandUp for Wind
Available from: 2012-11-01 Created: 2012-11-01 Last updated: 2017-11-28
7. Robust VAWT control system evaluation by coupled aerodynamic and electrical simulations
Open this publication in new window or tab >>Robust VAWT control system evaluation by coupled aerodynamic and electrical simulations
2013 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 59, 193-201 p.Article in journal (Refereed) Published
Abstract [en]

A control system for a vertical axis wind turbine is presented.The control strategy is to determine the electric load solely from the rotational velocity and the characteristics of the turbine, thus measurement of the incoming wind velocity is not required.The control system is evaluated with an aerodynamic vortex model coupled with an electrical model.Three different sets of control system parameters are tested, due to the trade off between high power absorption and achieving a fast system with high stability.The control systems are tested against a reference strategy where the wind speed is known.The simulations show that the three control systems provide a similar power absorption as the reference case.For dynamic cases, with fast changes in wind speed, the fast control strategies are beneficial.All control strategies are stable throughout the simulations when proper power absorption characteristics of the turbine are used. It is also shown that if peak power absorption is estimated at a too low tip speed ratio, the control strategies may inadvertently stop the turbine.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Wind power, VAWT, Darrieus Turbine, Control system, Numerical simulation, Vortex method
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-183738 (URN)10.1016/j.renene.2013.03.038 (DOI)000320827300024 ()
Available from: 2012-11-01 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved
8. Aerodynamic and electrical evaluation of a VAWT farm control system with passive rectifiers and mutual DC-bus
Open this publication in new window or tab >>Aerodynamic and electrical evaluation of a VAWT farm control system with passive rectifiers and mutual DC-bus
2013 (English)In: Renewable energy, ISSN 0960-1481, E-ISSN 1879-0682, Vol. 60, 284-292 p.Article in journal (Refereed) Published
Abstract [en]

A wind farm with a simple electrical topology with passive rectifiers and a single inverter (mutual topology) is compared to a more complex topology where each turbine has a separate inverter (separate topology).In both cases, the turbines are controlled electrically by varying the extracted power with the rotational velocity as control signal.These two electrical topologies are evaluated with respect to absorbed power for a farm of four turbines placed either on a line or in a square formation.The evaluation is done with an aerodynamic vortex model coupled with an electrical system model.Simulations predict that individual control is beneficial for aerodynamically independent turbines if flow velocities differ significantly between turbines. If the differences in flow velocities are caused by one turbine operating in the wake of another, the deviations in power output between the topologies are less prominent.The mutual topology even deliver more power than the separate topology when one turbine is in the wake of another turbine if the wind speed changes rapidly.

Place, publisher, year, edition, pages
Elsevier, 2013
Keyword
Wind power, Wind farm, VAWT, Vortex model, Control system
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
urn:nbn:se:uu:diva-183739 (URN)10.1016/j.renene.2013.05.028 (DOI)000323628600031 ()
Available from: 2012-11-01 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved
9. Adaptive fast multipole methods on the GPU
Open this publication in new window or tab >>Adaptive fast multipole methods on the GPU
2013 (English)In: Journal of Supercomputing, ISSN 0920-8542, E-ISSN 1573-0484, Vol. 63, 897-918 p.Article in journal (Refereed) Published
National Category
Computer Science Computational Mathematics Energy Engineering
Identifiers
urn:nbn:se:uu:diva-183731 (URN)10.1007/s11227-012-0836-0 (DOI)000315162400018 ()
Projects
UPMARCeSSENCE
Available from: 2012-10-25 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved

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Citation style
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  • en-US
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  • nn-NO
  • nn-NB
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  • Other locale
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Output format
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