Fundamental investigation into output-based prediction of whirl flutter bifurcations

Abstract

This paper investigates an approach for predicting whirl flutter bifurcations using pre-flutter output data. The approach leverages the critical slowing down phenomenon, which makes aeroelastic systems recover to equilibrium from disturbances more slowly when closer to the flutter boundary. By quantifying this phenomenon based on output data from pre-flutter transient responses, one can predict the flutter onset and the amplitude of limit-cycle oscillations (bifurcation diagram). The approach is demonstrated for a propeller-nacelle system using output data from transient simulations. Bifurcation diagrams are predicted within a few percentages of reference results using output data at two forward speeds, as low as 25% to 30% below the whirl flutter speed. Extensive sensitivity analyses highlight the accuracy and robustness of predictions for various output data choices and levels of nonlinearity, providing insights for future applications to higher-complexity systems. This work opens a new path to predicting whirl flutter bifurcations during the design of aeroelastic systems prone to this instability.