Multicyclic Control for Vibration Reduction of Coaxial Rotor System with High-Fidelity Fluid-Structure Coupling

The present study explores the active vibration suppression of a lift-offset (L.O.) coaxial rotor system in high-speed forward flight by applying a multicyclic controller with individual blade control (IBC) actuation. A high-fidelity vibration analysis is conducted through a loose-coupling (LC) framework that combines a compressible 3D (three-dimensional) CFD (Computational Fluid Dynamics) solver with a comprehensive aeromechanics (CA) method. Since the upper and lower rotor experience different aerodynamic environments, an asynchronous or different IBC actuation for each rotor is applied to achieve greater vibration reduction performance than the usual synchronous or identical actuation. Open-loop control results indicate that the asynchronous actuation suppresses the vibratory loads more effectively, from which the best actuation inputs are identified and subsequently incorporated into the more involved closed-loop control. The validity of closed-loop controller is verified across all harmonic combinations indicating that the closed-loop controller yields additional vibration reduction as compared with the open-loop control case, overall resulting in up to 87.8% compared with the uncontrolled case. In addition, the asynchronous multicyclic IBC offers improved vibration reduction of about 3.1% as opposed to the counterpart synchronous actuation. The airloads distributions over the rotor disk before and after the optimum IBC actuation is also investigated to gain insights leading to the vibration reduction of the rotor system.