Aeroelastic Stability Analysis of Coaxial Rotors using Viscous Vortex Particle Method

摘要

Coaxial rotor helicopters are a candidate for the next generation of high speed rotorcraft. The stiff hingeless counter-rotating blades experience complex aerodynamic interactions very different from single rotor configurations, which may lead to vibrations and instability. Therefore, the aeroelastic behavior of coaxial rotors requires special attention. The Viscous Vortex Particle method can capture accurate non-linear vortex wake interactions with computational efficiency and is well suited for coaxial rotor wake calculations. In this study, the viscous vortex particle method is combined with an aeroelastic formulation for hingeless blades and a reduced order model for unsteady aerodynamic loads. The radial and azimuthal distribution of inflow over the rotor is periodic due to the blade passage effect. The aeroelastic stability of the periodic system is determined using numerical Floquet analysis. The coupling between the blade modes is characterized from the eigenvectors of the state transition matrix. The results indicate that the first lag mode and third flap mode of the blades can become unstable at high thrust.