Effects of inflow conditions and forcing on subsonic jet flows and noise

Large-eddy simulations of a circular jet with a Mach number M = 0.9 and a Reynolds number Rep = 4 x 10(5) are performed to investigate the effects of the inflow conditions on flow development and the sound field. Three parameters are varied in the jet inflow: the forcing amplitude, the shear-layer thickness, and the use of the first modes in the ring vortex excitation involving several azimuthal modes. The most significant modifications in the jet features are found in the latter case: When the first four azimuthal modes are removed from the forcing, the jet develops much more slowly with reduced turbulence intensities, and the jet is quieter. Moreover, links between the sound levels and the turbulence intensity peaks are observed. The downstream sound levels vary like the peak amplitudes of the centerline turbulence intensity, and the sideline sound levels vary like those of the fluctuating radial velocity in the shear layer.