Fundamental Studies of Subsonic and Transonic Flow Separation. Part 2. Second Phase Summary Report

The work reported herein represents the second phase of a fundamental study of subsonic and transonic flow separation. The detailed features of the turbulent boundary layer flow separation induced by a forward-facing step in transonic and high subsonic flow were studied. The influences of an upstream disturbance upon the downstream separation were simulated by several shallow- cavity models of different depth to length ratios. The free-stream conditions were varied over the ranges M 0.6 to approx. 0.9 and Reft 5 x 10 to 6th power to approx. 30 x 10 to the 6th power It was shown that certain upstream disturbances can produce higher separation pressure and skin friction than related to a single forward-facing step. A separation pressure correlation was established empirically from the cavity flow data. It was observed that a certain Reynolds number and depth-to-length-ratio cavity yielded a maximum separation pressure. At the same time, an increase of free-stream Mach number continuously increased the separation pressure. The flow relaxation along the cavity floor was explored by systematic measurements and analysis of surface pressures and velocity profiles. These studies revealed that the flow relaxation started from the floor and spread outward. Therefore, the lower portion of the outer layer of the shear flow contained a longer memory, carrying the influence of the upstream disturbance to the downstream separation. The law of the wall and the wake was used for the analysis of the velocity distributions and the estimation of the skin friction. It was found that the slope of the law of the wall is different for velocity profiles of different strengths of wake.