The Mixing Transition in Free Shear Flows
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The term “mixing transition” denotes an increase in molecular mixedness observed in a shear flow which has earlier experienced the conventional (momentum) transition from laminar flow. First defined by Konrad (1976), from measurements of concentration in a free shear layer, the transition has been described and measured by a number of other methods, in particular by flow visualiztion, by measurement of chemical reaction product and by hot-wire anemometry, in aqueous as well as gaseous flows. In this presentation we review some of the measurements and try to assess what insight they may give on several questions that occur. 1. What is the relation of the mixing transition to Reynolds number and to other events: the momentum transition; vortex pairing; development of streamwise vortex structure? 2. How much does interfacial area increase during the transition? 3. How fast does this occur? 4. Does chaotic advection play a role? The answers are tentative and incomplete.
KeywordsReynolds Number Shear Layer Vortex Structure Vortex Pairing Streamwise Vortex
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