Predictions of the Acoustic Nearfield on a Carrier Deck

A numerical method for extrapolating jet noise from near-field microphone array to far field points will be developed. This software is needed to provide the source function to enable the Navy to use a commercial acoustic propagation code to predict the noise levels at the crew locations of aircraft carrier decks. The ultimate goal is to determine the benefit of applying noise reduction technology such as chevron nozzles. The nozzles will be tested in acoustic measurement facilities and the results will be transferred to the operating environment using the software. A sophisticated extrapolation model is required because the source of supersonic jet noise is highly extended and coherent, rendering simple point source models invalid. Several groups approach this problem by considering a source distribution on a conical surface surrounding the jet, and making microphone measurements on this surface. In contrast, this effort will consider the source to be within the jet plume, where it actually is, and the microphones outside the flow, where they are. Correct location of the source will simplify the measurements and the numerical effort. A novel technique that has elements in common with near-field acoustic holography and beamforming will be applied.