Inflow Model Effects on Propeller Whirl Flutter

This paper investigates inflow model effects on propeller whirl flutter focusing on a propeller-nacelle test case from classical whirl flutter theory. The model is implemented into the Rotorcraft Comprehensive Analysis System framework considering two approaches to capture the inflow on the propeller disk: a uniform inflow model and the viscous vortex particle method. The whirl flutter speed for each inflow model is predicted by extrapolating damping values estimated from free decays. Parametric analyses assess how the inflow model impacts the results for various propeller angular velocities and solidity. The viscous vortex particle method yields a higher whirl flutter speed than the uniform inflow model, and the difference widens with the propeller angular velocity and solidity. While the uniform inflow model generally predicts the same whirl flutter speed for a given solidity, the viscous vortex particle method captures differences between varying the number of blades and the blade chord.