SBIR-STTR Award

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.

Benefit:
The Navy will be able to evaluate the benefit of jet noise reduction hardware. The algorithms developed in the project will enhance the ability of OptiNav's commercial microphone phased arrays to deal with coherent source distributions. This will lead to more array sales and product improvements where the arrays are applied.

Keywords:
microphone phased array, microphone phased array, boundary element code, Jet noise, Chevron nozzle, nearfield acoustic holography, beamforming

An efficient acoustic holography technique for characterizing the noise source of tactical aircraft jet plumes was developed through the bench testing stage in Phase I. A full-scale array of 100 microphone locations was designed to be able to capture the noise of an F-18 in a simulated carrier launch, including effects of deck scrubbing and interactions with the jet blast deflector, in a few seconds of data acquisition. In Phase II, the technique and the array will be tested in model scale using the Small Hot Jet Acoustic Rig and the NASA-Glenn Research Center and in full scale at the Naval Air Station Patuxent River.

Benefit:
NAVAIR will have a state-of-the-art jet noise measurement system that can be used to support the Navys jet noise reduction project and other Government acoustic needs. OptiNav will have a new capability to offer to its government and industrial customers.

Keywords:
Jet noise, tactical aircraft noise, acoustic holography, beamforming