Assessment of Cavity Covered with Porous Surface in Controlling Shock/Boundary-Layer Interactions in Hypersonic Intake

Abstract

The supersonic/hypersonic flow through an aircraft intake must be decelerated before entering the combustion chamber to ensure efficient combustion. Retardation in the flow speed is achieved through a progression of oblique and normal shock waves in the isolator region of the intake. However, the advantages of speed reduction in intake are usually accompanied by huge losses due to the shock wave and boundary-layer interactions (SBLIs). These losses may include, inlet-unstart, abrupt thickening or separation of the boundary layer, unsteady shock oscillations, etc. Clearly, the SBLIs must be controlled to minimize the losses and improve the performance of the complete vehicle. Control of these interactions by manipulating the strength of the shock using a shallow cavity with wall ventilation has gained prominence. In this study, the efficacy of a thin porous surface deployed over shallow cavity in the higher adverse pressure gradient regions of Mach 5.7 and Mach 7.9 mixed-compression intakes, is experimentally investigated. With the variation of diameter and pitch of the pores, the porosity in Mach 5.7 intake is varied as; 4.5%, 7.5%, 17%, 21.6%, and 25%. A maximum of 20.53% drop in static pressure in the Mach 5.7 intake controlled by the cavity covered with 25% surface perforation, at a near-reattachment location (x/L = 0.73), is observed. However, the separation bubble in Mach 5.7 intake is suppressed most efficiently, when the cavity is covered with 17% porous surface. For Mach 7.9 intake also, the 25% surface perforation has maintained its superiority in reducing the wall static pressure to a maximum of 20.20% at x/L = 0.73. Once again, the 17% porous surface controlled configuration is found to be quite effective in suppressing the bubble. A qualitative investigation of the Schlieren images supports the findings of wall static pressure data.