Experimental study on noise reduction of a wavy multi-copter rotor

In order to alleviate rotor noise of multi-copters, a wavy rotor is modified from the baseline (BL) rotor by shifting every other cross section toward the trailing edge. Utilizing balance and far-field microphones, aerodynamic and acoustic performance of the wavy rotor is analysed. The aerodynamic performance of the wavy rotor is approximately the same as the BL rotor in terms of available thrust and power loading. Reduction of tonal noise in the middle-frequency range is observed for high RPM (Revolutions Per Minute) values, which is consistent with the trend of thrust spectra. Broadband noise decrease in the high frequency range is noticed for all RPM values. The noise reduction in the circumferential range corresponding to the advancing blade is larger than that of the retreating blade. The decrease of overall sound pressure level (OASPL) of the wavy rotor with respect to the BL rotor is about 1.4 ~ 2 dB.