Design and calibration of a small aeroacoustic beamformer

Abstract

The use of aeroacoustic beamforming has increased dramatically in the past decade. The primary driving force behind this has been the need to improve the noise characteristics of aircraft and automotive vehicles, coupled with ever increasing computer processing power. Aeroacoustic beamforming is an experimental technique that uses an array of microphones located in the far field of acoustic noise sources generated by a body in air flow. Each microphone measures an acoustic magnitude and relative phase based on its unique position with respect to the acoustic source(s). Beamforming algorithms process this data, typically to generate spatial noise source plots over a two dimensional grid at each frequency of interest. Much of the available aeroacoustic beamforming literature presents results at relatively high frequencies corresponding to large facilities, scale models, and available budgets, which can potentially set unrealistic goals for the development of a small-scale university research facility. This paper details the design and calibration of a small aeroacoustic beamformer, designed to investigate airfoil trailing edge noise for low to moderate Reynolds number flows. The optimisation of the microphone array, based on spatial, air flow and financial constraints, is presented. The algorithms which were used to calculate the beamformer outputs are described, as well as the array calibration process, including beamforming of various noise sources in an anechoic environment. The array is shown to successfully detect and accurately locate both tonal and broadband noise sources.