Abstract
The flow field around a rotationally oscillating circular cylinder in a uniform flow is studied by using a particle image velocimetry to understand the mechanism of drag reduction and the corresponding suppression of vortex shedding in the cylinder wake at low Reynolds number. Experiments are conducted on the flow around the circular cylinder under rotational oscillation at forcing Strouhal number 1, rotational amplitude 2 and Reynolds number 2,000. It is found from the flow measurement by PIV that the width of the wake is narrowed and the velocity fluctuations are reduced by the rotational oscillation of the cylinder, which results in the drag reduction rate of 30%. The mechanism of drag reduction is studied by phase-averaged PIV measurement, which indicates the formation of periodic small-scale vortices from both sides of the cylinder. It is found from the cross-correlation measurement between the velocity fluctuations that the large-scale structure of vortex shedding is almost removed in the cylinder wake, when the small-scale vortices are generated at the unstable frequency of shear layer by the influence of rotational oscillation.
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Nobuyuki Fujisawa: After graduating from Tohoku University (D.E. 1983), he joined Gunma University and worked as an associate professor since 1991. He has been a professor of Niigata University since 1997. He is interested in flow visualization, non-intrusive measurement and control of thermal and fluid flow phenomenon in engineering and science.
Masaru Ugata: He was educated at Niigata University (B.E. 2003). He is now working in Fujii corporation.
Tomokazu Suzuki: He was educated at Niigata University (B.E. 2000) and Graduate School of Niigata University (M.E. 2002). He is now working in Fuji Heavy Industries.
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Fujisawa, N., Ugata, M. & Suzuki, T. A study on drag reduction of a rotationally oscillating circular cylinder at low Reynolds number. J Vis 8, 41–48 (2005). https://doi.org/10.1007/BF03181601
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DOI: https://doi.org/10.1007/BF03181601