Large-eddy and detached-eddy simulation of an incompressible flow past an open cavity

Abstract

The three-dimensional incompressible flow past a rectangular two-dimensional (2D) shallow cavity in a channel is investigated using Large Eddy Simulation (LES) and Detached Eddy Simulation (DES). The length to depth ratio of the cavity is L/D=2 and the Reynolds number defined with the cavity depth and the mean velocity in the upstream channel is 3,360. In LES, the sensitivity of the flow around the cavity to the characteristics of the upstream flow is studied by considering two extreme cases. In the first case a developing laminar boundary layer is present upstream the cavity while in the second case the upstream flow is fully turbulent. The two simulations are compared in terms of the mean statistics and temporal physics of the flow, including the dynamics of the coherent structures in the region surrounding the cavity. The structure and spectral content of the flow over the cavity are considerably affected by the characteristics of the upstream flow. For the laminar inflow case it is found that the flows becomes unstable but remains laminar as it is convected over the cavity. Due to the 3D flow instabilities and the feedback mechanism, the spanwise vortices that are shed regularly from the leading cavity edge are disturbed in the spanwise direction and, as they approach the trailing edge corner, break into an array of hairpin-like vortices that is convected downstream the cavity close to the channel bottom. In the fully turbulent inflow case the jittering of the shear layer on top of the cavity by the incoming near wall coherent structures strongly influences the formation and convection of the organized eddies inside the separated shear layer and induces a large decrease in feedback coherence. In both simulations the large scale structures in the shear layer region induce large scale pressure fluctuations at the trailing cavity edge and convection of patches of vorticity inside the cavity parallel to the trailing edge. These patches modulate the intensity of...