A study of the interaction between a glancing shock wave and a turbulent boundary layer : the effects of leading edge bluntness and sweep

Abstract

The effects of leading edge bluntness and sweep angle on the three dimensional glancing shock wave - boundary layer interaction have been investigated. A large number of hemi-cylindrically blunted fins with leading edge diameter ranging from 0 to l.Oin, with leading edge sweep angles between 0° and 75° were tested. The incidence angle was varied from 0° to 21°. The shock wave from each configuration interacted with a fully developed turbulent boundary layer growing along the tunnel side wall. The free stream Mach number in the 9in x 9in continuous flow supersonic wind tunnel was 2.4 and the Reynolds number based on boundary layer thickness was 5 x 10^. Experimental investigations included oil smear tests, surface pressure surveys, schlieren pictures of the inviscid shock envelopes and shock structure in the plane of symmetry. The study highlighted the significant effects of bluntness and sweep on the scale and character of the interaction. While bluntness intensified the interaction, sweep alleviated its intensity. The most dramatic effect of sweep angle was observed when the leading edge was swept from 0° to 30°. Sufficiently outboard of the plane of symmetry, the features of blunt and sharp fins became similar. The boundary between the inner "bluntness dominated" and the outer "viscous dominated" regions shifted inboard at the higher incidence and sweep angles. The characteristic surface oil flow patterns showed little change for sweep angles up to A = 60°. Leading edge bluntness increased the scale of the interaction almost linearly while leaving its character unchanged. The multiplicity of the separation and attachment lines on the side wall and the fin surface, suggested a system of vortices in the interaction region. Flow field models have been proposed over the range of sweep angles considered in the present study. The number and strength of the vortices is seen to depend on the leading edge bluntness, sweep and the incidence angle. The important parameters governing the primary separation distance and the peak pressure in the plane of symmetry have been identified. Correlation formulae suggest a strong interdependence of the various parameters concerned.