Analysis on influence of aerodynamic interference on noise characteristics of coaxial rigid rotor in hover
Based on the computational fluid dynamics(CFD)method and noise solved FW-H(Ffowcs Williams-Hawkings)equation,the aeroacoustic noise of rigid coaxial rotor was calculated in hover,and the influence of aerodynamic interference on noise characteristics was analyzed.The study indicated that:in hover stage,the surface pressure of upper and lower rotor blades changed periodically with the rotation of the blade,and there were eight small cycles in one revolution;the periodic variation of the sound source led to inconsistent"superposition effect"produced by the sound pressure at observation points in different directions in the plane of the rotor disk,and the noise level at the intersection of upper and lower rotors was higher than that at other azimuths;due to the time-varying load,there was still significant radiation noise in the direction of the rotation axis,so the noise sound pressure level in this direction was much larger than that of single rotor.With the increase of rotor spacing,aerodynamic interference between twin rotors was reduced,and the normal force fluctuation of the maximum noise sound pressure level on the sound radiation sphere also decreased.
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