Design and use of microphone directional arrays for aeroacoustic measurements

An overview of the development of two microphone directional arrays for aeroacoustic testing is presented. These arrays were specifically developed to measure airframe noise in the NASA Langley Quiet Flow Facility. A large aperture directional array using 35 flush-mounted microphones was constructed to obtain high resolution noise localization maps around airframe models. Complementing the large array is a small aperture directional array, constructed to obtain spectra and directivity information from regions on the model. Both arrays are employed in acoustic measurements of a 6 percent of full scale airframe model consisting of a main element NACA wing section with a 30 percent chord half-span flap. Representative data obtained from these measurements are presented, along with details of the array calibration and data post- processing procedures.