Shock tunnel experiments on control of shock induced large separation bubble using boundary layer bleed

Shock–Boundary Layer Interaction (SBLI) often occurs in supersonic/hypersonic flow fields. Especially when accompanied by separation (termed strong interaction), the SBLI phenomena largely affect the performance of the systems where they occur, such as scramjet intakes, thus often demanding the control of the interaction. Experiments on the strong interaction between impinging shock wave and boundary layer on a flat plate at Mach 5.96 are carried out in IISc hypersonic shock tunnel HST-2. The experiments are performed at moderate flow total enthalpy of 1.3 MJ/kg and freestream Reynolds number of 4 million/m. The strong shock generated by a wedge (or shock generator) of large angle 30.96° to the freestream is made to impinge on the flat plate at 95 mm (inviscid estimate) from the leading edge, due to which a large   separation bubble of length (75 mm) comparable to the distance of shock impingement from the leading edge is generated. The experimental simulation of such large separation bubble with separation occurring close to the leading edge, and its control using boundary layer bleed (suction and tangential blowing) at the location of separation, are demonstrated within the short test time of the shock tunnel (∼600 μs∼600 μs) from time resolved schlieren flow visualizations and surface pressure measurements. By means of suction – with mass flow rate one order less than the mass flow defect in boundary layer – a reduction in separation length by 13.33% was observed. By the injection of an array of (nearly) tangential jets in the direction of mainstream (from the bottom of the plate) at the location of separation – with momentum flow rate one order less than the boundary layer momentum flow defect – 20% reduction in separation length was observed, although the flow field was apparently unsteady.