Acoustic Source Localization Using a 3-d Microphone Array in a Mach 1.3 Jet

A 3-D microphone array was developed and used to locate the origins of individual sound waves that were created within a high-speed and 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 the array was not equipped to deal with an off axis distribution of noise sources. Further, the registration of sound radiation from similar events within the mixing layer was observed to depend on whether the events 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 using a Hartmann tube fluidic actuator (HTFA), and its use to locate noise sources within a Mach 1.3 jet. The 3-D array and its accompanying noise source location algorithm appear to be quite robust and accurate as they accurately predicted the location of noise sources from an HTFA and the expected radial distribution of noise sources of a high-speed jet. The array will be used with simultaneous temporally resolved flow visualizations to further explore jet noise sources. Introduction This paper presents progress of an ongoing work that is being conducted on an ideally expanded Mach 1.3 axisymmetric jet. The purpose of the work is to relate the development and interaction of large structures within the jet's mixing layer to radiated far field noise. This paper presents the development and use of a three-dimensional microphone array that will be used to perform laser based flow diagnostics with simultaneous far field acoustic measurements for noise source localization. Some of the pertinent results from previous papers 1-3 will be reviewed in this introduction as well as other papers that directly relate to the development of the array.