Aerodynamics and near-field acoustics of a subsonic cylindrical cavity flow by parallel CFD

Two cylindrical cavities of diameter to depth ratio L/D = 0.71 and L/D = 2.5 were investigated by numerical modelling. The flow was modelled using three different approaches at free-stream Mach numbers 0.235 and 0.3. These models were an inviscid flow prediction, a viscous flow prediction, where the dissipation was given only by the laminar viscosity and by the numerical dissipation, and a turbulent flow prediction, where the energy dissipation at the small scales of turbulence was modelled by Detached Eddy Simulation (DES). Single domain decomposition (SDD) and recursive domain decomposition (RDD) MPI parallelization algorithms were developed along with the DES model to run mesh refined tests. The parallelization efficiency of the two methods was investigated and the advantages and disadvantages of these were shown. The mesh-converged results of the L/D = 0.71 cylindrical cavity have been compared to experiment. Two counter-rotating convective vortices at the cavity downstream edge were found. The vortex core locations at various streamwise planes were located using streamlines of the spanwise and flow-normal time mean velocity components. The radiating pressure field directivity in the L/D = 0.71 and L/D = 2.5 was investigated at a 5L radial distance from the cavity centre. The two L/D configurations are characterized by a similar upstream directivity. The L/D = 0.71 cavity is louder and displays a secondary downstream peak. In the spanwise plane, the acoustic wave from the L/D = 2.5 cavity is asymmetric whereas it is symmetric in the L/D = 0.71 cavity. “Rossiter modes” and duct modes are found to co-exist in the cylindrical cavity. The Power Spectral Density (PSD) of the wall pressure from experiment and computation over the Mach number range 0 to 0.235 show an amplification of these modes at coincidence for the L/D = 0.71 cavity.