Self-Sustained Oscillations of Turbulent Flow in an Open Cavity

Abstract

Direct numerical and large eddy simulations of incompressible turbulent flows over deep and shallow cavies were performed in the range of 600 <= Re(D) <= 12, 000 to investigate the influence of the incoming turbulent boundary layer on self-sustained oscillations of the shear layer. When the turbulent boundary layer approached the open cavity with Re(D) = 3000, the energy spectra of the pressure fluctuations showed spectral peaks in the range of 0.15 <= omega <= 0.3. Conditionally averaged flowfields disclosed that the spectral peaks arise from the separation of high-speed streaky structures rather than from a geometric singularity of the cavity. The same spectral peaks were observed in a backward-facing step flow as well as in deep and shallow cavity flows, despite the different geometries of these systems. In the turbulent cavity flow of Re(D) = 12, 000, however, the peak frequencies of the energy spectra cavity lengths of L/D = land 2 were found to correspond to the Nth modes with N = 2 and 3, respectively. These modes were very similar to the frequency characteristics of self-sustained oscillations reported for laminar cavity flows. Inspection of instantaneous pressure fluctuations as well as spanwise-averaged pressure fluctuations reversed that regular shedding of quasi-two-dimensional vortical structures was responsible for the peak frequency in the energy spectra.