Assessment and comparison of the performance of functional projection beamforming for aeroacoustic measurements

Functional Projection Beamforming (FPB) is a method proposed by Dougherty in 2019, based on functional beamforming. It yields the integrated sound spectrum for a given region of integration (ROI) within the functional beamforming source map. FPB does not suffer from the loss of level that can affect functional beamforming, especially for coarse scan grids, high frequencies and high values of the exponent parameter n. This paper investigates the application of FPB to three different experimental cases: (1) a single speaker emitting broadband noise with a low signal to noise ratio, (2) two closely–placed speakers emitting two incoherent broadband noise signals, and (3) trailing–edge noise measurements of a tripped NACA 0018 airfoil. All measurements were performed with a 64–microphone array in the anechoic open–jet wind tunnel of Delft University of Technology. The performance of FPB is assessed in terms of the accuracy of the frequency spectra obtained and compared with several other well–known acoustic imaging methods. Overall, FPB shows satisfactory results for the three cases investigated, especially for distributed sources, such as trailing– edge noise