Self-sustained oscillations in shock wave/turbulent boundary layer interaction

The interaction of a spatially developing supersonic turbulent boundary layer with an impinging oblique shock wave is analyzed by means of direct numerical simulation of the compressible Navier-Stokes equations. Under the selected flow conditions a small recirculation zone is observed, and a shear layer with embedded large vortical structures forms near the average separation point, Such structures are mainly responsible for the amplification of noise and turbulence across the interaction zone; high acoustic loads of O(170)dB are found which are strictly related to the Reynolds shear stress distribution. The interaction of the vortical structures with the foot of the incident shock produces pressure waves that propagate in the upstream direction, thus exciting the instability modes of the shear layer and promoting the formation of additional vortical structures. In the interaction zone discrete low-frequency tones are generated due to an acoustic resonance mechanism that shows similarities with the acoustic mechanisms typical of cavity flows and screeching jets. In order to support our claim, we develop a simplified model that is supported by the analysis of the two-point pressure covariances, and that is capable to reasonably predict the characteristic frequencies of the tones. Copyright © 2006 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.