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Session: Advances in Aeroelastic Prediction and Design Optimization for Next-Generation Aerospace Vehicles - Dr. Cristina Riso
Session starts: Wednesday 19 June, 08:30
Presentation starts: 08:30

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Sai Vishal Gali (Georgia Institute of Technology)
Cristina Riso (Georgia Institute of Technology)

Abstract:
This paper presents a novel output-based approach for predicting flutter bifurcations in periodic aeroelastic systems, with application to rotorcraft blade flutter. When a rotorcraft is in forward flight, aerodynamic loads vary with the azimuth location, bringing periodic effects into the rotor blade dynamics. Flutter bifurcations of rotorcraft blades and other periodic aeroelastic systems are traditionally studied via Floquet theory or a sweep of transient responses, yielding a high computational burden for large-scale numerical models. This paper investigates a new approach that leverages ongoing research by the authors in output-based whirl flutter prediction for time-invariant aeroelastic systems. The proposed approach involves identifying the recovery rate to equilibrium from envelope functions associated with pre-flutter transient responses for as few as two parameter values (e.g., two advance ratios). The recovery rates for each amplitude are then extrapolated to find the corresponding parameter value that yields zero recovery rate at that amplitude, corresponding to a flutter point or a limit-cycle oscillation solution. The multiple frequencies present in the transient responses of periodic systems, which challenge the envelope identification, are addressed by isolating the dominant frequency associated with the bifurcating dynamics via a bandpass filter. The proposed approach is demonstrated for transient responses from an analytical blade model from the rotorcraft aeroelasticity literature. Figure 1 shows initial results for the originally linear model, resulting in amplitude-constant recovery rates. The proposed approach predicts flutter at an advance ratio of 0.75, matching the literature results. The paper will systematically investigate the accuracy, computational efficiency, and numerical robustness of the approach for various choices of the output data and incorporate nonlinear effects into the blade model to assess the ability to predict limit-cycle oscillations. Overall, the paper will make new contributions to the area of non-intrusive flutter bifurcation analysis for periodic aeroelastic systems.