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High-frequency forcing of a turbulent axisymmetric wake

Published online by Cambridge University Press:  31 March 2015

Anthony R. Oxlade ,
Jonathan F. Morrison ,
Ala Qubain  and
Georgios Rigas
Anthony R. Oxlade
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2AZ, UK
Jonathan F. Morrison*
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2AZ, UK
Ala Qubain
Affiliation:
Mustakbal Clean Tech, PO Box 5272, Amman 11183, Jordan
Georgios Rigas
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2AZ, UK
*
†Email address for correspondence: [email protected]
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Abstract

A high-frequency periodic jet, issuing immediately below the point of separation, is used to force the turbulent wake of a bluff axisymmetric body, its axis aligned with the free stream. It is shown that the base pressure may be varied more or less at will: at forcing frequencies several times that of the shear layer frequency, the time-averaged area-weighted base pressure increases by as much as 35 %. An investigation of the effects of forcing is made using random and phase-locked two-component particle image velocimetry (PIV), and modal decomposition of pressure fluctuations on the base of the model. The forcing does not target specific local or global wake instabilities: rather, the high-frequency jet creates a row of closely spaced vortex rings, immediately adjacent to which are regions of large shear on each side. These shear layers are associated with large dissipation and inhibit the entrainment of fluid. The resulting pressure recovery is proportional to the strength of the vortices and is accompanied by a broadband suppression of base pressure fluctuations associated with all modes. The optimum forcing frequency, at which amplification of the shear layer mode approaches unity gain, is roughly five times the shear layer frequency.

JFM classification

Flow Control: Instability control Turbulent Flows: Turbulence control Wakes/Jets: Wakes
Type
Papers
Information
Journal of Fluid Mechanics , Volume 770 , 10 May 2015 , pp. 305 - 318
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Copyright
© 2015 Cambridge University Press 

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