A Study of Mach 0.75 Jets and Their Radiated Sound Using Large-Eddy Simulation

Large-Eddy Simulations (LES) of a compressible nozzle/jet conguration have been car-ried out. Two jets were simulated, an isothermal jet and a jet with a higher temperature than the quiescent surrounding air. The Mach number was in both cases 0.75 and the jet Reynolds number was 5.0 10 . Sound pressure levels in far-eld observer locations were evaluated using Kirchhoff surface integration. The Favre ltered Navier-Stokes equations were solved using a nite volume method solver with a low-dissipation third-order up-wind scheme for the convective uxes, a second-order centered difference approach for the viscous uxes and a three-stage second-order Runge-Kutta technique in time. The computational domain was discretized using a block structured boundary tted mesh with approximately 3.0 10 cells. The calculations were performed on a parallel computer, us-ing message-passing interface (MPI). A compressible form of Smagorinsky's subgrid scale model was used for computation of the subgrid scale stresses. Absorbing boundary con-ditions based on characteristic variables were adopted for all free boundaries. Velocity components specied at the entrainment boundaries were estimated from corresponding Reynolds Averaged Navier-Stokes (RANS) calculations, which enable the use of a rather narrow domain. This, furthermore, ensures that the correct amount of uid is entrained into the domain. Two-point space-time correlations were obtained for locations in the shear layer center, from which length and time scales of turbulence structures were eval-uated. Predicted near-eld ow statistics and far-eld sound pressure levels (SPL) are both in good agreement with experiments. Predicted (SPL) are for all observers locations, where evaluated, within a 3.0 [dB] deviation from measured levels and for most locations within a 1.0 [dB] deviation. Experimental data used for validation were provided by Labo-ratoire d'Etude Aeródynamiques, Poitiers, France