Simulation of Instabilities and Sound Radiation in a Jet

The inflow and near field of a jet that is excited by an axial mass source located in the potential core are simulated numerically. The simulation takes into account the spreading of the jet. Comparison is made with experimental results for both excited and unexcited jets. It is shown that many of the features observed experimentally are due to the instability of the mean profile (i.e., the large-scale structures) and not due to the turbulence. The instability is shown to generate low-frequency sound. The terms identified by Ribner as the shear noise terms are shown to be responsible for this sound generation.