Development and evaluation of a 3-D microphone array to locate individual acoustic sources in a high-speed jet

A 3-D microphone array was developed, evaluated, and used to locate the origins of individual sound waves that were created within a high-speed, high Reynolds number, turbulent jet. In previous work by the authors, a linear array of microphones and simultaneous temporally resolved flow visualizations were used to determine the origin of individual sound waves and their generation mechanisms within the jet. The linear array algorithm assumed the noise sources were distributed along the jet axis, and was not able to resolve off-axis locations of noise sources. Further, the registration of sound radiation from similar phenomena within the mixing layer was observed to depend on whether the phenomena occurred on the array side of the jet or the opposite side. Based on these error sources and observations, a new array was developed that can locate the individual sources of sound waves within three dimensions. This work presents the development of this array, its validation, and its use to locate noise sources within a high-speed jet. The 3-D array with its accompanying noise source location algorithm is quite robust and accurate as it predicted the precise location of noise sources from a plasma arc, a high-frequency fluidic device, and the expected radial distribution of noise sources from a high-speed jet.