Comparison of two- and three-dimensional turbulent cavity flows

In this paper, the near-field unsteady hydrodynamics and acoustics of two- and three-dimensional cavity flows are studied with the use of computational aeroacoustics and unsteady Reynolds-Averaged Navier-Stokes (RANS) simulations. The one-equation Spalart-Allmaras turbulence model and the Detached Eddy Simulation (DES) have been implemented to account for the turbulent nature of the flow field. In order to avoid the severe grid clustering in the vicinity of solid wall boundaries in RANS calculations, and to increase the allowable time step for high-fidelity unsteady calculations, a simple wall function has been used to model the wall-bounded flow. The agreement between simulations with the use a fine turbulent grid and a simple wall function is good. Comparisons of two- and three-dimensional turbulent cavity flows have been performed. The cavity has a L/D ratio of 4.4, and a W/D ratio of 1.0 for the three-dimensional case. The Mach and Reynolds numbers are held constant at 0.6 and 200,000 respectively. For the threedimensional case, the flow field is observed to oscillate in the "shear layer mode," with a feedback mechanism that follows Rossiter's formula. On the other hand, the self-sustained oscillating flow transitions to a "wake mode" for the two-dimensional simulation, with more violent fluctuations inside the cavity.