Experimental investigation of flow separation associated with a step or a groove.

Abstract

Low-speed measurements were made on the flow separation associated with a backward-facing step or a rectangular groove by determining the distribution of pressure along the surface and the distributions of mean and fluctuating velocities across several transverse sections. The pressure distribution was found to be rather insensitive to the changes in step height and thickness of the approaching boundary layer. This can be understood by realizing that the cavity flow behind the step is maintained in equilibrium such that the pressure exerted by the solid surface is balanced by the turbulent shear stress, which is set up in the mixing region approximately independently of the step height and the approaching boundary layer. The flow over a groove is markedly different according as it is deep or shallow, the demarcating value of depth-breadth ratio beind around 0.7. The deep-groove type of flow is characterized by a comparatively smooth flow and a low value of pressure drag. The converse is true of the shallow grooves. The cavity flow region inside the groove is maintained in equilibrium similarly as in the case of flow over a step.