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Effect of turbulence on the wake of a wall-mounted cube

Published online by Cambridge University Press:  09 September 2016

R. Jason Hearst ,
Guillaume Gomit  and
Bharathram Ganapathisubramani
R. Jason Hearst
Affiliation:
Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK
Guillaume Gomit
Affiliation:
Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK
Bharathram Ganapathisubramani*
Affiliation:
Engineering and the Environment, University of Southampton, Southampton SO17 1BJ, UK
*
†Email address for correspondence: g.bharath@southampton.ac.uk
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Abstract

The influence of turbulence on the flow around a wall-mounted cube immersed in a turbulent boundary layer is investigated experimentally with particle image velocimetry and hot-wire anemometry. Free-stream turbulence is used to generate turbulent boundary layer profiles where the normalised shear at the cube height is fixed, but the turbulence intensity at the cube height is adjustable. The free-stream turbulence is generated with an active grid and the turbulent boundary layer is formed on an artificial floor in a wind tunnel. The boundary layer development Reynolds number ( $Re_{x}$ ) and the ratio of the cube height ( $h$ ) to the boundary layer thickness ( $\unicode[STIX]{x1D6FF}$ ) are held constant at $Re_{x}=1.8\times 10^{6}$ and $h/\unicode[STIX]{x1D6FF}=0.47$ . It is demonstrated that the stagnation point on the upstream side of the cube and the reattachment length in the wake of the cube are independent of the incoming profile for the conditions investigated here. In contrast, the wake length monotonically decreases for increasing turbulence intensity but fixed normalised shear – both quantities measured at the cube height. The wake shortening is a result of heightened turbulence levels promoting wake recovery from high local velocities and the reduction in strength of a dominant shedding frequency.

JFM classification

Turbulent Flows: Turbulent boundary layers Turbulent Flows: Turbulent Flows Wakes/Jets: Wakes

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Papers
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Journal of Fluid Mechanics , Volume 804 , 10 October 2016 , pp. 513 - 530
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© 2016 Cambridge University Press 

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