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The structure of a separating turbulent boundary layer. Part 2. Higher-order turbulence results

Published online by Cambridge University Press:  20 April 2006

Roger L. Simpson ,
Y.-T. Chew  and
B. G. Shivaprasad
Roger L. Simpson
Affiliation:
Southern Methodist University, Dallas, Texas 75275
Y.-T. Chew
Affiliation:
Southern Methodist University, Dallas, Texas 75275 Present address: Department of Mechanical and Production Engineering, University of Singapore.
B. G. Shivaprasad
Affiliation:
Southern Methodist University, Dallas, Texas 75275
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Abstract

The velocity-probability-distribution flatness and skewness factors for u and v are reported for the separating turbulent boundary layer described by Simpson, Chew & Shivaprasad (1981). Downstream of separation the skewness factor for u is negative near the wall, whereas it is positive upstream of separation. The flatness factor for u downstream of separation differs from the upstream behaviour in that it has a local maximum of about 4 at the minimum mean velocity location in the backflow. Both upstream and downstream of separation the skewness factor for v has a profile shape and magnitudes that are approximately the mirror image or negative of the skewness factor for u. The flatness factor for v seems to be affected little by separation.

Examination of the momentum and turbulence-energy equations reveals that the effects of normal stresses are important in a separating boundary layer. Negligible turbulence-energy production occurs in the backflow. Turbulence-energy diffusion is increasingly significant as separation is approached and is the mechanism for supplying turbulence energy to the backflow.

The backflow appears to be controlled by the large-scale eddies in the outer region flow, which provides the mechanism for turbulence-energy diffusion. The backflow behaviour does not appear to be significantly dependent on the far downstream near-wall conditions when the thickness of the backflow region is small compared with the turbulent shear layer thickness.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 113 , December 1981 , pp. 53 - 73
Copyright
© 1981 Cambridge University Press

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