Organized Self-Sustained Oscillations of Turbulent Flows over an Open Cavity

Abstract

Proper orthogonal decomposition was employed to turbulent flows over an open cavity to investigate the spatial characteristics of coherent structures responsible for self-sustained oscillations. The distributions of pressure fluctuations were analyzed by using snapshot-based proper orthogonal decomposition. When self-sustained oscillations took place for Re-D = 12, 000 in the cavity geometry of L/D = 2, three pairs of alternative patterns were shown in the first and second modes of pressure fluctuations. By examining both temporal evolutions and spanwise distributions of the first two modes, quasi-two-dimensional vortical formations were shown to be responsible for the self-sustained oscillations. In turbulent cavity flows of Re-D = 3000, however, the periodic oscillations were not observed, due to the irregular shedding of three-dimensional vortical structures. For the application of proper orthogonal decomposition analysis to experimental data, the decomposition was employed to the spatial distributions of v-v correlations on the lip line of cavity geometry.