This paper is motivated by the observed transonic limit cycle flutter of a high-aspect-ratio swept wing tested at DLR in Gottingen. We show that the aeroelastic mechanism responsible for the limit cycle flutter behavior can be explained in terms of the structural washout effect, which is strongly stabilizing at transonic Mach numbers. This limits the energy transfer rate to the wing, resulting in a limit cycle flutter mode where bending and torsion are almost perfectly in phase, and the streamwise wing section motion resembles a SDOF torsion mode with an axis of rotation forward of the leading edge. For swept wings, the apparent pitching motion of the wing sections arises naturally through the structural washout and is present in the first bending mode that enters LCO flutter. The aeroelastic washout effect may produce counterintuitive results, and increasing the dynamic pressure may actually be stabilizing. In such a case, decreasing the dynamic pressure would increase the LCO amplitude, and high-altitude transonic flutter becomes a real possibility. The results demonstrate the importance of using a nonlinear structural model in these calculations. If a linear structural model is used, the critical dynamic pressure at LCO flutter onset is overpredicted by a factor of nearly 3, and the predicted flutter mode is at a frequency much higher than was observed during wind tunnel tests.
Transonic limit cycle flutter of high-aspect-ratio swept wings
2006
15 Seiten, 28 Quellen
Aufsatz (Konferenz)
Englisch
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