Fast and slow changes of the length of gradient trajectories in homogeneous shear turbulence

Abstract

Gradient trajectories in scalar fields have recently received attention in the context of dissipation elements [1], [2] which in turn are of interest for the flamelet concept in nonpremixed combustion [3]. Dissipation elements are space filling regions in a scalar field defined such that gradient trajectories starting from any point within the element in ascending and descending directions reach the same minimum and maximum points. Gradient trajectories advance preferentially through regions of the scalar field that have been smoothed by the combined action of diffusion and extensive strain. Since the extensive strain in these regions is of the order of the inverse of the integral time scale T, dimensional analysis predicts the mean length l _m of dissipation elements to be of the order of the Taylor length [4].