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Control of circular cylinder flow using distributed passive jets

Published online by Cambridge University Press:  13 June 2018

Ben L. Clapperton
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2AZ, UK
Peter W. Bearman
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2AZ, UK

Abstract

A wind tunnel study has been carried out to investigate flow control around a hollow circular cylinder using passive jets driven by naturally occurring pressure differences. Flow enters the cylinder through spanwise holes along the stagnation line and exits through a spanwise distribution of holes at $\pm 65^{\circ }$. The diameter of the entry and exit holes were 1 % and 0.5 % of the cylinder diameter, respectively. Reynolds numbers were at the upper end of the subcritical regime and ranged from $3\times 10^{4}$ to $2.8\times 10^{5}$. Jet spacings of 10 % and 20 % of the cylinder diameter were investigated, and the ratio of the average jet exit velocity to the cross-flow velocity at the boundary layer edge was found to rise to approximately 0.35 and 0.4, respectively, above a Reynolds number of $1.5\times 10^{5}$. Findings based on using the surface oil flow technique revealed a repeating, organised cellular pattern downstream of adjacent jet exit holes consisting of a primary counter-rotating vortex pair structure, followed by a secondary weaker pair. Downstream of adjacent exit holes, and centred midway between them, there exists a separation bubble which delays final flow separation compared with the flow directly downstream of a jet. The variation in the angular position of boundary layer separation across the span had the effect of suppressing von Kármán vortex shedding. This resulted in a drag coefficient, at the upper end of the Reynolds-number range studied, 14.5 % lower than that found using trip wires to initiate boundary layer transition.

Type
JFM Papers
Copyright
© 2018 Cambridge University Press 

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