Coupled Mode Flutter Analysis of Turbomachinery Blades Using an Adaptation of the p–k Method

Current trends in turbomachinery design significantly reduce the mass ratio of structure to air, making them prone to flutter by aerodynamic coupling between mode shapes, also called coupled-mode flutter. The p–k method, which solves an aeroelastic eigenvalue problem for frequency and damping, respectively, excitation of the aerodynamically coupled system, was adapted for turbomachinery application using aerodynamic responses computed in the frequency domain (FD). A two-dimensional (2D) test case is validated against time-marching fluid–structure coupled simulations for subsonic and transonic conditions. A span of mass ratios is investigated showing that the adapted p–k method is able to predict the transition between aeroelastically stable and unstable cascades depending on the mass ratio. Finally, the p–k method is applied to a low mass ratio fan showing that the flutter-free operating range is significantly reduced when aerodynamic coupling effects are taken into account.