Eddies, streams, and convergence zones in turbulent flows

TLDR

Turbulent shear flows are better understood by describing them in terms of individual events or streamline patterns, which dominate key averages such as kinetic energy, Reynolds stress, and chemical mixing, especially in convergence (C) regions and recirculating eddies. The project aimed to use numerical simulations to develop criteria for defining eddying or vortical zones. The authors defined convergence (C) and streaming (S) zones to characterize the entire flow field. The analysis revealed that homogeneous and sheared turbulent flows consist of distinct eddy, C, and S zones, and provided objective criteria that identify regions of circulating, converging, diverging, and high‑velocity streamlines.

Abstract

Recent studies of turbulent shear flows have shown that many of their important kinematical and dynamical properties can be more clearly understood by describing the flows in terms of individual events or streamline patterns. These events or flow regions are studied because they are associated with relatively large contributions to certain average properties of the flow, for example kinetic energy, Reynolds stress, or to particular processes in the flow, such as mixing and chemical reactions, which may be concentrated at locations where streamlines converge for fast chemical reactions (referred to as convergence or C regions), or in recirculating eddying regions for slow chemical reactions. The aim of this project was to use the numerical simulations to develop suitable criteria for defining these eddying or vortical zones. The C and streaming (S) zones were defined in order to define the whole flow field. It is concluded that homogeneous and sheared turbulent flow fields are made up of characteristic flow zones: eddy, C, and S zones. A set of objective criteria were found which describe regions in which the streamlines circulate, converge or diverge, and form high streams of high velocity flow.