Aeroacoustic beamforming of a model wind-turbine in anechoic and reverberant environments

In order to obtain a better understanding of the noise radiated by wind turbines, rotors and fans, acoustic measurements were performed using a small-scale plyon-mounted rotor. The rotor, which operates at 900 RPM, is composed of 3 equally spaced NACA 0012 blades. The chord and length of the blades are 70 mm and 450 mm respectively. The pitch angle of the blades is set to either 0, 5, 10 or 15 degrees; the blades are not twisted, nor are they tapered. The rotor was placed in 2 environments: an anechoic room at the University of Adelaide and a reverberant wind tunnel test section in the UNSW aerospace research laboratory. The purpose of this paper is to investigate the effects of the hard-walls of the wind tunnel on the acoustic measurements. The acoustic radiation was measured using a 64-microphone acoustic array and processed using a conventional beamforming (CBF) algorithm. The main source of sound for all cases is located at the blade tip. The blade-plyon (or tower) interaction is clearly visible with a pitch angle of 0 degrees in the third octave [1600; 3200] Hz range. The effects of the reverberant environment are presented. While the main source is located at the same position in the two configurations, which means that acoustic measurements can be performed in the reverberant test section without any additional treatment, there are important differences between the measurements.