Towards Hybrid Mesh Large Eddy Simulation for Jet Aeroacoustics

Large Eddy Simulation (LES) is a potentially useful tool for the prediction of jet noise. Previous work in this area has mainly used simple structured meshes which do not have the geometric flexibility to handle industrial applications. An unstructured hybrid mesh LES solver is described and applied to a free jet and an impinging jet problem. The methodology includes an adaptive scaling of the Roe Flux Dierence Splitting upwind term to retain robustness when capturing shock waves whilst being small in other regions to avoid excessive dissipation of eddies. The multiple element type allows regular hexahedral elements in regions such as shear layers, with tetrahedral elements filling space to the far field. This results in a reduction of nodal unknowns compared to a structured mesh with the same eective resolution. Results for a Mach 0.9 free jet are in agreement with experiment and comparable to previously published work. Computation of a high nozzle pressure ratio supersonic impinging jet captures the unsteady nature of the impingement recirculation bubble and is in qualititative agreement with PIV measurements. The unsteadiness of the recirculation bubble produces large variations in the wall jet, which appears to be a major noise source. Pressure spectra indicate a peak at a Strouhal number of 0.5 in agreement with experimental measurement.