Three-dimensional instabilities of compressible flow over open cavities

We developed a three-dimensional algorithm for direct numerical simulations (DNS) of open cavity flow to extend a previous study of cavity oscillations (JFM 455:325-346, 2002). Complementary methodologies for extracting information about global instabilities (including their receptivity and optimal control) of two- and three-dimensional cavity flows have been implemented. For a low Mach number cavity with length-to-depth ratio of two, the two-dimensional steady flow was found unstable to three-dimensional (spanwise homogeneous) disturbances that consist of a spanwise modulation of the recirculating vortex interior to the cavity. The oscillations are unstable over a narrow band of spanwise wavelengths comparable to the cavity depth, and oscillatory in time, but with a very low frequency (about 10 times lower than the two-dimensional Rossiter mode). Results from simulations for different cavity aspect ratios and Mach numbers will also be presented.