Large Eddy Simulations of Sound Radiation from Subsonic Turbulent Jets

Abstract

Large eddy simulations (LES) of subsonic turbulent jets, including the near-field flow and far-field sound radiation, were performed using two different subgrid-scale turbulence models. Two different cases were considered. As a validation case, predictions from a Mach 0.9, Reynolds number 3.6 × 10 3 randomly forced turbulent jet were performed. Both the near-field velocity statistics and far-field sound directivity were found to be in excellent agreement with previous experimental data and direct numerical simulation (DNS) results. The second case involved a Mach 0.4, Reynolds number 5 x 10 3 harmonically forced jet. Both axisymmetric and azimuthal inlet disturbances were imposed to facilitate detailed comparisons to recent DNS of axisymmetric jet sound, and to highlight the effects of small-scale turbulence. As part of this second case, the validity of Kirchhoff's method for far-field sound prediction was also assessed in conjunction with LES and the effect of the subgrid-scale turbulence model on sound radiation was examined. The sound source location and levels were different between the three-dimensional turbulent jets and similar two-dimensional axisymmetric laminar jets. Far-field sound radiation predictions, obtained using Kirchhoff's method, were in good agreement with the directly predicted LES results. LES predictions obtained with the dynamic Smagorinsky and the dynamic mixed subgrid-scale turbulence models were similar, although the mixed model resulted in higher turbulence and sound levels. The directivity was not uniform as predicted by Lighthill's theory for a fully turbulent jet, but exhibited a preferred radiation angle between 35 and 70 deg in agreement with reported experimental data from an acoustically excited jet.