The existence of three-dimensional perturbations in the reattachment of a two-dimensional supersonic boundary-layer after separation

Abstract

Presented to the Wind Tunnel and Model Testing Panel of the Advisory Group for Aeronautical Research and Development Boundary-Layer Research Meeting London , April 25-29, 1960. The reattachment region of a laminar boundary-layer af ter separation has been investigated in TCEA facilities at a Mach number of 2.16. Two-dimensional compression-corners and backward or forward facing step models were used. The case of interaction between a shock-wave and a laminar boundary-layer was also considered. Surface flow was observed by a sublimation technique and detailed span-wise surveys were made in the reattachment region of the flow with total-head probes. Strong, regular and repeatable span-wise perturbations were observed in the boundary-layer; these could not be explained by irregularities either in the air-flow upstream of the models or in the models themselves. It was found in all cases that street-like flow perturbations existed up to the point where transition occurred. A systematic investigation was made on backward facing steps in order to find out the effects of step height and boundary-layer thickness on the wave-length of the flow perturbations.