Impact of array upgrades on jet noise source location measurements

For the past 10 years, GTRI has been using an acoustic beamformer a 1-m Vogel spiral array to perform jet noise source location measurements. It was found that the current 1-m array was unable to spatially resolve noise sources in jet configurations such as supersonic jets and twin jets owing to the compact distribution of shock diamonds and the spacing between nozzles. More specifically, the current array was able to provide unambiguous source localization between 1000 Hz and 30 kHz, while resolving the noise sources listed above would benefit from improved low-frequency resolution. Recently, a new, larger array was designed and built to specifically eliminate the issues discussed above. The design process and calibration of this new array is outlined in this work. A demonstration of the improved capabilities is shown by comparing cases of insufficient array performance using the old array to newly collected data with the new array: using jet noise source location measurements for supersonic shock-containing jets and subsonic twin jets. The new array has been installed in GTRI’s large anechoic facility, which additionally contains 30 far-field microphones mounted on three separate polar arcs. This work also examines using these microphones in addition to the new array to further improve low-frequency measurements.