Aerodynamic characteristics analysis of electrically controlled rotor based on viscous vortex particle method

Abstract

An electrically controlled rotor (ECR), also called as swashplateless rotor, replaces a swashplate with a trailing edge flap system to implement primary rotor control. To investigate the aerodynamic characteristics of the ECR, an analysis model based on the viscous vortex particle method, ECR blade pitch equation and Weissinger-L lifting surface model is established. In this model, the ECR wake flow field vorticity is discretized as multiple vortex particles, and the vorticity-velocity form Navier-Stokes equation is solved to simulate the transport diffusion of the vorticity. The impact of flap deflection on the blade bound vortex circulation is calculated via the equivalent incidence angle. The flap deflection induced blade pitch movement is obtained by solving the ECR blade pitch movement equation via the Runge-Kutta fourth-order method. On this basis, to address the low computing efficiency of the viscous vortex wake model, a “relaxation difference”-based trim strategy is developed to reduce the calculation times of the viscous vortex wake model during trim iteration. Based on this model, the aerodynamic characteristics of a sample ECR in hovering and forward flight conditions are analysed. The results show that in hovering and forward flight conditions, when the rotor trim requires large flap deflection, in the rotor wake vorticity field, apart from blade tip vortex, there are intense vortices at both ends of the flap. This additional intense vortex results in an ECR wake vorticity distribution that is more complex than that of a conventional rotor, significantly impacting the distribution of the rotor disc inflow and load. Additionally, in the forward flight condition, the ECR flap collective deflection results in cyclic blade pitch movement, while flap cyclic deflection results in a significant portion of the 2Ω harmonic component in the blade pitch movement when the advance ratio is high.