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On turbulent separation in the flow past a bluff body

Published online by Cambridge University Press:  26 April 2006

A. Neish  and
F. T. Smith
A. Neish
Affiliation:
Department of Mathematics, University College London, Gower Street. London WC1E 6BT. UK
F. T. Smith
Affiliation:
Department of Mathematics, University College London, Gower Street. London WC1E 6BT. UK
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Abstract

The basic model problem of separation as predicted by the time-mean boundary-layer equations is studied, with the Cebeci-Smith model for turbulent stresses. The changes between laminar and turbulent flow are investigated by means of a turbulence ‘factor’ which increases from zero for laminar flow to unity for the fully turbulent regime. With an attached-flow starting point, a small increase in the turbulence factor above zero is found to drive the separation singularity towards the trailing edge or rear stagnation point for flow past a circular cylinder, according to both computations and analysis. A separated-flow starting point is found to produce analogous behaviour for the separation point. These findings lead to the suggestion that large-scale separation need not occur at all in the fully turbulent regime at sufficiently high Reynolds number; instead, separation is of small scale, confined near the trailing edge. Comments on the generality of this suggestion are presented, along with some supporting evidence from other computations. Further, the small scale involved theoretically has values which seem reasonable in practical terms.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 241 , August 1992 , pp. 443 - 467
Copyright
© 1992 Cambridge University Press

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