Journal of Fluid Mechanics

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

Paul E.  Dimotakis a1 and Garry L.  Brown a1p1
a1 Graduate Aeronautical Laboratories, California Institute of Technology, Pasadena
p1 pres University of Adelaide, Australia.

Article author query
dimotakis pe   [Google Scholar] 
brown gl   [Google Scholar] 


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.

(Published Online April 11 2006)
(Received November 7 1975)
(Revised March 19 1976)