Abstract
This work visualizes the flow surrounding a scaled model vertical axis wind turbine at realistic operating conditions. The model closely matches geometric and dynamic properties—tip speed ratio and Reynolds number—of a full-size turbine. The flow is visualized using particle imaging velocimetry (PIV) in the midplane upstream, around, and after (up to 4 turbine diameters downstream) the turbine, as well as a vertical plane behind the turbine. Time-averaged results show an asymmetric wake behind the turbine, regardless of tip speed ratio, with a larger velocity deficit for a higher tip speed ratio. For the higher tip speed ratio, an area of averaged flow reversal is present with a maximum reverse flow of \(-0.04U_\infty\). Phase-averaged vorticity fields—achieved by syncing the PIV system with the rotation of the turbine—show distinct structures form from each turbine blade. There were distinct differences in results by tip speed ratios of 0.9, 1.3, and 2.2 of when in the cycle structures are shed into the wake—switching from two pairs to a single pair of vortices being shed—and how they convect into the wake—the middle tip speed ratio vortices convect downstream inside the wake, while the high tip speed ratio pair is shed into the shear layer of the wake. Finally, results show that the wake structure is much more sensitive to changes in tip speed ratio than to changes in Reynolds number.
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Acknowledgments
The authors wish to thank Matthew Glasstone and Allen Schultz for their experimental assistance. We thank Antonio Posa and Elias Balaras for much insightful discussion and many helpful suggestions. Thank you to The Metro Washington Chapter of the Achievement Rewards for College Students (ARCS) Foundation and the McNichols Foundation for their financial support of my education.
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Parker, C.M., Leftwich, M.C. The effect of tip speed ratio on a vertical axis wind turbine at high Reynolds numbers. Exp Fluids 57, 74 (2016). https://doi.org/10.1007/s00348-016-2155-3
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DOI: https://doi.org/10.1007/s00348-016-2155-3