Vibration Reduction of Coaxial Rotor by Blade Installation Phase Angle

Abstract

Aerodynamic lift variations of an isolated coaxial rotor system were analyzed by a computational fluid dynamics (CFD) approach. The study focused on a coaxial rotor configuration equipped with four blades per rotor and employed rFlow3D, a CFD solver specifically tailored for rotorcraft analyses. The analysis focuses on the high-speed forward flight with an advance ratio of 0.6 or higher, which is the ratio of the forward speed to the rotor tip speed. The numerical findings demonstrate a significant reduction in lift variation and reveal that the appropriate inter-rotor phase angle holds the potential to minimize the fluctuation to a level akin to that experienced during hovering. This reduction can be attributed to the mitigation of the vibrational component associated with the number of blades per rotor revolution. A detailed analysis further reveals that the pitching and rolling moments exhibit opposing changes in response to variations in the inter-rotor phase angle.