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Predicting Whirl Flutter Bifurcations Using Pre-Flutter Output Data

AIAA 2023-1308
Session: Special Session: Advances in Whirl Flutter Testing and Prediction
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This paper explores an approach for predicting whirl flutter bifurcations using output data in the pre-flutter regime. The approach leverages the critical slowing down phenomenon, which causes aeroelastic systems to recover from disturbances more slowly as they operate closer to the flutter boundary. By quantifying how the recovery rate changes with a control parameter (\textit{e.g.}, forward speed) and amplitude, it is possible to predict the flutter boundary and a range of the bifurcation diagram. Recent studies in geometrically nonlinear wings have shown that this approach enables accurate yet computationally tractable flutter bifurcation analyses of large-dimensional aeroelastic systems. This paper explores the approach applied to whirl flutter for the first time. The study uses output data from an analytical isolated rotor model representative of classical whirl flutter. The proposed approach predicts the whirl flutter point and a range of the bifurcation diagram within less than 1% of direct time marching while only requiring two transient responses in the pre-flutter regime. Predictions remain accurate even using output data at forward speeds 30% lower than the whirl flutter speed. These results are a step toward tackling realistic configurations affected by whirl flutter, with the ultimate goal to help design advanced vertical lift concepts while avoiding this destructive phenomenon.