COHERENT STRUCTURES AND CONDITIONAL STATISTICS IN INHOMOGENEOUS TURBULENT MIXING

We study the statistics of a passive scalar mixed by a turbulent flow that contains coherent structures (Gortler vortices). These structures entrain the passive scalar in such a way that its one-point probabili ty density function (pdf) has a nonstandard shape that can be explaine d as a superposition of a background Gaussian mixing on the one hand, and the action of the Gortler vortices on the other. We propose a ''me an field'' approach to predict this pdf. This study (applicable to a w ider class of systems) constitutes the first experimental example for which the conditional expectation of the second temporal derivative of the concentration of a passive scalar given the concentration deviate s from a linear behavior.