Coupled Mode Flutter Analysis of Turbomachinery Blades using an Adaptation of the P-K Method

Abstract

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.

A two-dimensional 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.