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Simulations of a vertical axis turbine in a channel
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.
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. Vol. 63, 477-485 p.
Keyword [en]
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: urn:nbn:se:uu:diva-183737DOI: 10.1016/j.renene.2013.09.038ISI: 000330488100054OAI: oai:DiVA.org:uu-183737DiVA: diva2:563994
Available from: 2012-11-01 Created: 2012-11-01 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Fluid Mechanics of Vertical Axis Turbines: Simulations and Model Development
Open this publication in new window or tab >>Fluid Mechanics of Vertical Axis Turbines: Simulations and Model Development
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
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:nbn:se:uu:diva-183794 (URN)978-91-554-8539-9 (ISBN)
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

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Goude, AndersÅgren, Olov

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