Oscillatory Control of Shock-Induced Separation

Abstract

An experimental investigation, aimed at delaying e ow separation as a result of the occurrence of a shockwave/boundary-layer interaction, is reported. The experiment was performed using a NACA 0015 airfoil at highReynolds-number incompressible and compressible e ow conditions. The effects of Mach and Reynolds numbers were identie ed, using the capabilities of the cryogenic-pressurized facility to maintain one parameter e xed and change the other. The main objectives of the experiment were to study the effects of periodic excitation on airfoil drag divergence and to alleviate the severe unsteadiness associated with shock-induced separation (known as buffeting). Zero-mass-e ux oscillatory blowing was introduced through a downstream directed slot located at 10% chord on the upper surface of the NACA 0015 airfoil. The effective frequencies generated 2 ‐4 vortices over the separated region, regardless of the Mach number. Even though the excitation was introduced upstream of the shock wave, it had pronounced effects downstream of it. Wake dee cit (associated with drag ) and unsteadiness (associated with buffeting ) were reduced. The spectral content of the wake pressure e uctuations indicates steadier e ow throughout the frequency rangewhen excitation isapplied. This is especially evident at low frequencieswhich are more likely to interact with the airframe.