Progress and Problems in Understanding Turbulent Shear Flows

Abstract

This discussion will be focussed on the plane turbulent mixing layer, featured in the illustration on the front of the program of this meeting. Another example of it is shown in Figure 1, while Figure 2 is a diagram which defines the basic parameters of this simplest of turbulent shear flows. Throughout this discussion the higher speed U₁ will always be in the upper part of the diagram. The speed ratio U₂/U₁ will therefore always be less than unity, but the density ratio ρ₂/ρ₁ may be less than or greater than unity. In high-speed flow the Mach numbers M₁ and M₂ would also be parameters. In fact, our interest in this problem was initially addressed to the question of how the characteristics of the flow depend on the density ratio, it having been supposed by many investigators that this was the parameter governing the observed, strong variations of spreading angle in the shear layer at the edge of a supersonic flow (M₁ > 1, M₂ = 0).