Inlet streamwise vorticity effects on jet evolution and far field sound generation

A computational aero-acoustics model consisting of a vortex filament based flow solver and Lighthill's analogy is presented and employed in a study of inlet streamwise vorticity effects on flow and noise generated by a high-speed subsonic jet. The model shows that, in the presence of small amounts of inlet streamwise vorticity, the flow large-scale structure is drastically changed and is characterized by coherent structures that are related to the imposed inlet streamwise vorticity pattern. These changes are accompanied with increased spreading, mixing and turbulence of the jet. The inlet streamwise vorticity field achieves these effects by reorienting the predominately azimuthal vorticity at the inlet. The far field sound is reduced at low and increased at high frequencies. These trends are related to suppression of low-order modes and enhancement of higher-order ones.