Experimental investigation on the aeroacoustics of coaxial rotors

Abstract

Coaxial rotor configurations are adopted by drones and electric vertical take-off and landing vehicles due to the need of generating high propulsive power within a compact size. The aerodynamic interaction between two closely spaced rotors may induce different noise features than isolated ones. This study presents an experimental investigation into the noise radiated from two small-scale coaxial contra-rotating rotors operated at different working configurations in an anechoic chamber. The noise was measured at 18 observer points using linear microphone arrays. The thrusts and torques of both rotors were measured independently. When the two rotors were operated at the same speed, the blade-overlapping position was regulated using a synchrophasing control technique. The results reveal that the relative phase angle of the rotors has a significant impact on the noise directivity patterns. The effects of axial separation distance on both spectral characteristics and noise directivities are also presented. This study provides insights into the low-noise design and operation for aerial vehicles using coaxial rotor configuration.