Heat transfer on secondary injection surface with backward-facing step influenced by hole location in supersonic flow field

The backward-facing step (BFS) with secondary injection is used for flame holding in the scramjet. BFS increases heat transfer through shear layer reattachment, while secondary injection increases heat transfer through various pressure waves and vortices. Combining these elements generates complex flow phenomena in supersonic flow, making it essential to measure and analyze detailed heat transfer characteristics experimentally. This study investigates the effects of hole location on heat transfer, focusing on the interactions between flow over the step and secondary injection. The supersonic blow-down wind tunnel achieved Mach 3, the operating condition of the internal scramjet. The heat transfer coefficients were measured using the transient IR thermography technique. Hole locations were selected in the shear layer reattachment region at C/H = 3,4 and beyond it at C/H = 5, where H and C represent the height of BFS and the center position of the hole, respectively. The results show that the hole location is the critical parameter in determining the merging of the shear layer and secondary injection. A specific hole location that maximizes heat transfer due to interactions between the recompression shock and bow shock is identified. These results offer valuable insights into the thermal design of supersonic vehicles, traditionally focused on aerodynamic improvement.