On the importance of specifying appropriate nozzle-exit conditions in jet noise prediction

In this paper, the importance of initial conditions on subsonic jet noise is emphasized by showing numerical results obtained by large-eddy simulations for initially laminar round jets at Mach number 0.9 and Reynolds number 105. The near and the far sound pressure fields of the jets are found to significantly vary with the flow parameters, namely the boundary-layer thickness and the turbulence levels, at the nozzle exit. With respect to initially turbulent jets, strong additional noise components generated by pairings of coherent vortical structures in the transitional shear layers are in addition observed, in agreement with experiments.