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Turbulence in a separated boundary layer

Published online by Cambridge University Press:  26 April 2006

M. Dianat  and
Ian P. Castro
M. Dianat
Affiliation:
Department of Mechanical Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK Present address: Safety Modelling Division, Midlands Research Station, British Gas ple, Solihull. UK.
Ian P. Castro
Affiliation:
Department of Mechanical Engineering, University of Surrey, Guildford, Surrey GU2 5XH, UK
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Abstract

This paper presents and discusses the results of an extensive experimental investigation of a flat-plate turbulent boundary subjected to an adverse pressure gradient sufficiently strong to lead to the formation of a large separated region. The pressure gradient was produced by applying strong suction through a porous cylinder fitted with a rear flap and mounted above the boundary layer and with its axis in the spanwise direction. Attention is concentrated on the structure of the turbulent flow within the separated region and it is shown that many features are similar to those that occur in separated regions produced in a very dissimilar manner. These include the fact that structure parameters, like Reynolds stress ratios, respond markedly to the re-entrainment of turbulent fluid transported upstream from the reattachment region, the absence of any logarithmic region in the thin wall boundary layer beneath the recirculation zone and the lack of any effective viscous scaling in this wall region, and the presence of a significant low-frequency motion having timescales much longer than those of the large-eddy structures around reattachment.

Similarities with boundary layers separating under the action of much weaker pressure gradients are also found, despite the fact that the nature of the flow around separation is quite different. These similarities and also some noticeable differences are discussed in the paper, which concludes with some inferences concerning the application of turbulence models to separated flows.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 226 , May 1991 , pp. 91 - 123
Copyright
© 1991 Cambridge University Press

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