Large eddy simulation of sound radiation from a subsonic turbulent jet

Large Eddy Simulations (LES) of a harmonically forced, subsonic turbulent jet [M = 0.4, Re_D = 5000), including the near-field flow and far-field sound radiation, were performed using two different subgrid-scale turbulence models. Axisymmetric and azimuthal inlet disturbances were imposed to facilitate comparisons with recent axisymmetric simulations and highlight small-scale turbulence effects. The objectives were to: (1) compare aeroacoustics of a turbulent jet and a two-dimensional axisymmetric jet, (2) assess validity of Kirchhoff's method for far- field sound prediction in conjunction with LES, (3) examine effect of the subgrid-scale turbulence model on the sound radiation, and (4) compare jet sound directivity to experimental measurements and theory. Far-field sound radiation predictions, obtained using Kirchhoff's method, were in good agreement with the directly computed LES results. The LES results with the dynamic Smagorinsky and the dynamic mixed subgrid-scale models were similar, although the mixed model resulted in higher turbulence and sound levels. The directivity of the jet was in general agreement with Lighthill's theory and experimental measurements for a turbulent jet. The directivity was not uniform as for a fully turbulent jet, but exhibited a preferred radiation angle between 35° and 70° in agreement with experimental measurements from an acoustically excited jet.