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Zero and negative entrainment in turbulent shear flow

Published online by Cambridge University Press:  29 March 2006

M. R. Head  and
P. Bradshaw
M. R. Head
Affiliation:
Indian Institute of Technology, Kanpur
Permanent address: Engineering Department, University of Cambridge
P. Bradshaw
Affiliation:
Department of Aeronautics, Imperial College, London
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Abstract

In certain accelerated flows the entrainment in the boundary layer, as normally defined, may be either zero or negative; on the other hand, there is no reason to suppose, on physical grounds, that the spread of mean or fluctuating vorticity should cease or become negative in such flows. This paradox is resolved in the present paper. It is also shown that in the equilibrium turbulent sink-flow boundary layer, where the entrainment as normally defined is zero, the reduced advection along streamlines in the outer part of the layer comes about mainly through increased dissipation: there is no reason to assume any radical change in the turbulence structure.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 46 , Issue 2 , 29 March 1971 , pp. 385 - 394
Copyright
© 1971 Cambridge University Press

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References

Bradshaw, P. 1967 J. Fluid Mech. 29, 625.
Bradshaw, P., Ferriss, D. H. & Atwell, N. P. 1967 J. Fluid Mech. 28, 583.
Herring, H. J. & Norbury, J. F. 1967 J. Fluid Mech. 27, 541.
Launder, B. E. & Stinchcombe, H. S. 1967 Imperial College TWF/TN/21.
Rosenhead, L. 1963 Laminar Boundary Layers. Cambridge University Press.
[dagger] Recent data of Kovasznay & Blackwelder (private communication) show that this is a good approximation in highly accelerated flows.