Investigation on Heat Transfer Characteristics over Hypersonic Backward-Facing Step of a Blunt Plate

Abstract— The combined effect of leading-edge bluntness and backward-facing step (BFS) is critical because they affect the surface thermal loads and boundary layer transition of hypersonic vehicles, which involves engine design, passive thermal protection and aero-optical effect correction of infrared imaging window. This paper mainly studies heat flux distribution characteristics and flow structure over the backward-facing step on a flat plate with various leading-edge bluntness. The experiments were conducted in the Mach 6 hypersonic wind tunnel at various unit Reynolds numbers (from 6 × 106 to 1.8 × 107 m–1). The wall temperature was measured by temperature-sensitive paints (TSP) technique and the flow field was visualized by the nano-particles planar laser scattering (NPLS) system and schlieren technique. The results of heat flux distribution and flow structure showed that the leading-edge bluntness had little influence on recirculation region size but could effectively delay transition of the redeveloping boundary layer and reduce the surface heat flux intensity downstream of the step, and the reduction was most significant when the leading-edge diameter was equal to the step height.