Tonal Aeroacoustic Sources of a Cambered Airfoil using Wavelet Beamforming

At low Reynolds numbers, Re-c = 1.4 x 10(5) and Re-c = 1.8 x 10(5), and low angles of attack alpha = 0 degrees and alpha = 5 degrees, the aeroacoustic behaviour of the controlled diffusion (CD) airfoil has been investigated. For these conditions, the airfoil produces tones which are unsteady in nature as found in previous numerical and experimental investigations. Wavelet beamforming is used to investigate the behaviour of the acoustic sources on the pressure and suction sides of the airfoil. In order to improve the spatial resolution of the wavelet beamforming maps a novel technique based on a rho-PHAT-C generalised cross-correlation approach has been applied. The time-frequency domain study of the aeroacoustic source location on the CD airfoil has found that the dominant acoustic source is on the suction side of the airfoil in between the leading edge and the laminar separation bubble at the trailing edge, quantifying for the first time the actual acoustic feedback loop responsible for the intermittent tones. The unsteadiness in the source position significantly increases with Reynolds number. In the main hump of the acoustic spectra, source behaviour does not change with frequency or presence of a tonal peak.