Internal layers in turbulent free-shear flows

D Fiscaletti,O R H Buxton,A Attili

doi:10.1103/physrevfluids.6.034612

Abstract

In turbulent free-shear flows, layers of intense shear bound regions of nearly uniform momentum. The thickness of these layers scales as the Kolmogorov length scale and the velocity across these layers presents a jump of approximately 10% of the characteristic large-scale velocity of the flow. In layers of intense shear, rotation dominates, whereas in layers of intense scalar gradient, strain is prevalent.

Highlights

In turbulent flows developing within a quiescent and/or non-turbulent environment, a convoluted and intermittent layer separates the turbulent region from the external fluid
Internal layers were investigated both in a mixing layer and in a jet, in the range of Reynolds numbers based on the Taylor microscale 134 < Reλ < 275
Internal layers of intense shear were identified after applying a triple decomposition of the velocity gradient tensor into the sum of three different contributions, i.e. rigid-body rotation, elongation, and shear, in which only the shear component was used in the calculation of the vorticity

Summary

Introduction

In turbulent flows developing within a quiescent and/or non-turbulent environment, a convoluted and intermittent layer separates the turbulent region from the external fluid. Several studies presented conditional averages of streamwise velocity, vorticity, and scalar concentration conditioned on the position within the TNTI (Bisset et al [2], Westerweel et al [3], Westerweel et al [4], Gampert et al [5], Gampert et al [6], van Reeuwijk and Holzner [7], Attili et al [8], Chauhan et al [9]) These averages showed the existence of a steep jump of the aforementioned physical quantities across the TNTI of several different turbulent flows, both wall-bounded and boundary-free. Attili et al [8] and Gampert et al [6] reported a jump across the TNTI of a mixing layer, the concentration of a passive scalar across the internal layers has never been analyzed

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