Passive scalar tagging for the study of coherent structures in the plane mixing layer

Abstract

Data obtained from the two-dimensional numerical simulation of a plane mixing layer have been used to study the feasibility of tagging one side of the flow by a passive scalar and using the instantaneous concentration of the scalar to detect the typical coherent events in the flow. The study has shown that this technique works quite satisfactorily and yields results similar to those obtained by using the instantaneous vorticity as a detection criterion. The contribution from the coherent events to the time-averaged turbulent momentum and scalar transport has been estimated. It is found that this contribution is of the same order as the time-mean transport during most of the dynamical evolution of the coherent structure. However, it may attain very large values for short periods of time in the neighborhood of pairing. The increase is particularly spectacular in the case of the Reynolds shear stress. While the present findings obtained from a two-dimensional simulation seem to support earlier results obtained from actual experiments, it is desirable to conduct additional studies with three-dimensional simulations when they become available

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ORCID for N.D. Sandham: orcid.org/0000-0002-5107-0944

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