Wing and Propeller Aerodynamic Interaction Effects on Whirl Flutter Instability

Abstract

This paper addresses the aerodynamic interaction effects between a wing and a propeller on the whirl flutter boundary. A wing-pylon model with a propeller is defined and modeled in the Rotorcraft Comprehensive Analysis System, considering both a flexible and rigid wing. The aerodynamic interaction effects on the whirl flutter boundary between the wing and the propeller are examined for various inflow models, including the viscous vortex particle method (VVPM), uniform inflow, and dynamic inflow on the propeller, and uniform inflow and vortex wake on the wing. Results show that the whirl flutter boundary is overestimated when the propeller is modeled with the VVPM and aerodynamic interaction effects are neglected. The impact is more prominent for a flexible wing-pylon model. Other propeller aerodynamic inflow models and their associated interaction effects alter the damping trend and increase the flutter speed on a flexible wing-pylon model only, highlighting the need to model propeller wake at a higher fidelity. Using the VVPM model on the propeller and vortex wake on the wing, it was found that the wing-to-propeller aerodynamics interactions have the most significant impact on a rigid wing and flexible pylon model, while both wingto-propeller and propeller-to-wing interactions had a significant impact on a flexible wing-pylon model. The impact of aerodynamic interaction effects are also characterized with respect to the pylon-length-to-propeller-radius ratio by varying the pylon length. Results show that aerodynamic interactions have a more significant impact on damping at lower airspeeds, regardless of the pylon length. Aerodynamic interactions were also found to be destabilizing at both operational and windmilling conditions. Overall, aerodynamic interactions should be considered if induced inflow over the lifting surface is expected to be a significant portion of the total propeller disk inflow.