Large-Eddy simulation of subsonic turbulent jets and their radiated sound

Large-eddy simulations of a compressible nozzle/jet configuration have been carried 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 5.0x10(4). Sound pressure levels in far-field observer locations were evaluated using Kirchhoff surface integration. The Favre filtered Navier-Stokes equations were solved using a finite volume method solver with a low-dissipation third-order upwind scheme for the convective fluxes, a second-order centered difference approach for the viscous fluxes, and a three-stage second-order Runge-Kutta technique in time. The computational domain was discretized using a block structured boundary-fitted mesh with approximately 3.0 X 10(6) cells. The calculations were performed on a parallel computer, using messagepassing interface. A compressible form of Smagorinsky's subgrid-scale model was used for computation of the subgrid-scale stresses. Absorbing boundary conditions based on characteristic variables were adopted for all free boundaries. Velocity components specified at the entrainment boundaries were estimated from corresponding Reynolds-averaged Navier-Stokes calculations, which enable the use of a rather narrow domain. This, furthermore, ensures that the correct amount of fluid is entrained into the domain. Two-point space-time correlations were obtained for locations in the shear layer center, from which length and timescales of turbulence structures were evaluated. Predicted near-field flow statistics and far-field 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 Laboratoire d'Etude Aerodynamiques, Poitiers, France.