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Turbulence structure of a boundary layer beneath a turbulent free stream

Published online by Cambridge University Press:  26 April 2006

P. E. Hancock  and
P. Bradshaw
P. E. Hancock
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2BY, UK Present address: University of Surrey, Guildford, Surrey GU2 5XH, UK.
P. Bradshaw
Affiliation:
Department of Aeronautics, Imperial College, London SW7 2BY, UK Present address: Stanford University, Stanford, California, CA 94305, USA.
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Abstract

Measurements have been made in the turbulent boundary layer on a flat plate in the presence of grid-generated free-stream, turbulence with a wide range of lengthscales. The data include conditionally sampled averages in which free-stream fluid was distinguished from boundary-layer fluid by heating the latter. Free-stream turbulence increases the standard deviation of the hot–cold interface as a proportion of the boundary-layer thickness, whilst the average position is mainly dependent upon the lengthscale. The shear correlation coefficient of the boundary-layer fluid decreases, and it is shown that the change in structure is directly related to the fluctuating-strain rate.

Transport velocities representing the diffusion of turbulent kinetic energy and shear stress have opposite signs in the boundary-layer fluid to those in the free-stream fluid, and it is shown that they are also related to the fluctuating-strain rate.

Complete balances of turbulent kinetic energy and shear stress have been evaluated, dissipation and pressure–strain redistribution having been deduced by difference. The dissipation length scale $L\tau = (-\overline{uv})^{\frac{3}{2}}/\epsilon $ is little affected by free-stream turbulence, whereas the corresponding parameter based on turbulent energy instead of shear stress is strongly affected.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 205 , August 1989 , pp. 45 - 76
Copyright
© 1989 Cambridge University Press

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