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Published July 2016 | Published
Journal Article Open

A Kinematic Description of the Key Flow Characteristics in an Array of Finite-Height Rotating Cylinders


Experimental data are presented for large arrays of rotating, finite-height cylinders to study the dependence of the three-dimensional (3D) mean flows on the geometric and rotational configurations of the array. Two geometric configurations, each with two rotational configurations, were examined at a nominal Reynolds number of 600 and nominal tip-speed ratios of 0, 2, and 4. It was found that the rotation of the cylinders drives the formation of streamwise and transverse flow patterns between cylinders and that net time–space averaged transverse and vertical flows exist within the developed flow region of the array. This net vertical mean flow provides an additional mechanism for the exchange of momentum between the flow within the array and the flow above it, independent from the turbulent exchange mechanisms which are also observed to increase by almost a factor of three in a rotating array. As an array of rotating cylinders may provide insight into the flow kinematics of an array of vertical axis wind turbines (VAWTs), this planform momentum flux (both mean and turbulent) is of particular interest, as it has the potential to increase the energy resource available to turbines far downstream of the leading edge of the array. In the present study, the streamwise momentum flux into the array could be increased for the rotating-element arrays by up to a factor of 5.7 compared to the stationary-element arrays, while the streamwise flow frontally averaged over the elements could be increased by up to a factor of four in the rotating-element arrays compared to stationary-element arrays.

Additional Information

© 2016 by ASME. Contributed by the Fluids Engineering Division of ASME for publication in the JOURNAL OF FLUIDS ENGINEERING. Manuscript received September 4, 2015; final manuscript received December 25, 2015; published online April 22, 2016. Assoc. Editor: Daniel Maynes. The authors would like to thank D. B. Araya for many helpful discussions on data analysis and for sharing the preliminary results of his work which provided significant insight into the experimental modeling of turbines. The authors would also like to thank J. S. Weitzman, R. B. Zeller, and B. Sabala for their advice and support in the experiment setup. This work was supported by funding to A.E.C. from a NSF Graduate Research Fellowship and a Stanford Graduate Fellowship, by funding to J.O.D. from ONR N000141211047 and the Gordon and Betty Moore Foundation through Grant No. GBMF2645, and by funding from the Bob and Norma Street Environmental Fluid Mechanics Laboratory at Stanford University.

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October 20, 2023