Reynolds-Stress Closure Model for Conditional Variables

Abstract

Free boundaries of turbulent shear flows show an intermittent character with a sharp interface separating instantaneously turbulent and non-turbulent zones shown by Corrsin and Kistler (1954). Prediction models for turbulent shear flows did not take this intermittent character into account so far. In this paper a second order closure model for turbulent shear flows based on conditional variables (Dopazo 1977) is presented, that allows prediction of intermittency factor, zone-conditioned mean velocities and Reynolds-stresses. It is based on an earlier closure for intermittency factor, mean velocities and kinetic energy and dissipation rate (Byggstøyl and Kollmann 1981) which used the concept of turbulent pseudo-viscosity for the turbulent zone. The equations for conditional moments contain explicitly terms accounting for the relative motion of turbulent and non-turbulent zones and the transport of various quantities through it. Some of those terms are non-closed on the second-order level and their closure will be discussed. The resulting conditional Reynolds-stress model will be evaluated by comparison of calculated properties of thin shear flows with experimental results.