The Acoustic Imaging of the Broadband Dipole Sound Sources of Helicopter Rotor in the Wind Tunnel Test

Acoustic wind tunnel test is an important way to study the noise mechanism of helicopter rotors. The broadband dipole noise distribution of helicopter rotors can be obtained from the acoustic wind tunnel measurement, which can be extremely helpful in analyzing the pulsation noise mechanism of rotor blade surfaces. However, during acoustic imaging of broadband dipole sources, there is often a problem of unwanted noise interference from other experimental setups of the wind tunnel, such as the rotor shaft. To accurately visualize the broadband dipole sound sources, in this article, a moving dipole-type sources beamforming method suitable for the wind tunnel environment is proposed. The reduced-rank cyclic Wiener filter is first developed to extract the rotor broadband noise signal in wind tunnel tests; a beamforming method for moving dipole sound sources is then proposed according to the characteristics of the generation and propagation of the dipole sound sources. The BO105 helicopter rotor model is tested in the FL-17 aeroacoustic wind tunnel of the China Aerodynamics Research and Development Center (CARDC). The wind tunnel test results demonstrate that the method can effectively suppress noise interference in the wind tunnel and accurately extract and visualize broadband dipole sources of rotor blade surfaces.