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The mixing layer at high Reynolds number: large-structure dynamics and entrainment

Published online by Cambridge University Press:  11 April 2006

Paul E. Dimotakis  and
Garry L. Brown
Paul E. Dimotakis
Affiliation:
Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena
Garry L. Brown
Affiliation:
Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena University of Adelaide, Australia.
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Abstract

A turbulent mixing layer in a water channel was observed at Reynolds numbers up to 3 × 106. Flow visualization with dyes revealed (once more) large coherent structures and showed their role in the entrainment process; observation of the reaction of a base and an acid indicator injected on the two sides of the layer, respectively, gave some indication of where molecular mixing occurs. Autocorrelations of streamwise velocity fluctuations, using a laser-Doppler velocimeter (LDV) revealed a fundamental periodicity associated with the large structures. The surprisingly long correlation times suggest time scales much longer than had been supposed; it is argued that the mixing-layer dynamics at any point are coupled to the large structure further downstream, and some possible consequences regarding the effects of initial conditions and of the influence of apparatus geometry are discussed.

Type
Research Article
Information
Journal of Fluid Mechanics , Volume 78 , Issue 3 , 7 December 1976 , pp. 535 - 560
Copyright
© 1976 Cambridge University Press

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