Noise Phase Characteristics and the Noise Cancellation of Twin-Coaxial Rotor Based on Phase Modulation Method

A noise prediction method based on CFD method and Ffowcs Williams–Hawkings (FW–H) equation is adopted to the prediction of the two-blade coaxial rotor, studying the noise characteristics of coaxial rotor, including the value and the distribution of SPL. According to the directionality of the SPL distribution, a Compass–Scissors Model (CSM) of coaxial rotor is established for the description of the orientation of noise distribution and the phase of sound wave. A combined coaxial rotor called twin-coaxial rotor consisting of two coaxial rotors is put forward according to the noise distribution characteristics of coaxial rotor, and the phase modulation method is applied so that the noise produced by the lower coaxial rotor and the upper coaxial rotor can be suppressed by the proper superposition of the sound waves. The simulation results show that producing the same lift, the noise cancellation using phase modulation method can reach 16 dB, confirming the potential of the noise reduction, and the optimal relationship of the compass angle difference and the scissors angle difference are also obtained. The establishment of CSM and the twin-coaxial rotor can also be meaningful for the noise suppression based on phase modulation method of multiple coaxial rotor systems.