Abstract
We investigate the mechanism of self-sustained oscillations over a rectangular cavity with a length-to-depth ratio of 2:1 by directly solving the compressible Navier-Stokes equations. The boundary layer over the cavity is turbulent and the freestream Mach numbers are M =0.4 and 0.7. The results clarify that the self-sustained oscillations occur in the shear layer of the cavity and two-dimensional large-scale vortices are formed in the shear layer of the cavity. When these vortices collide with the downstream edge, expansion waves are radiated. The propagation of the acoustic waves at the upstream edge produces disturbances in the shear layer. The disturbances are developed by the Kelvin-Helmholtz instability and finally the two-dimensional large-scale vortices are formed. As a result, a feedback loop is formed and the self-sustained oscillations occur. [This abstract is not included in the PDF]
