Wind tunnel investigation of transonic limit cycle flutter

Abstract

Transonic wind tunnel tests were conducted for a high aspect ratio aeroelastic wing model in order to clarify bifurcation characteristics of the limit cycle oscillation (LCO). During the tests, a large amplitude LCO (LC-H) and a small amplitude LCO (LC-1) appeared in a way as saddle-node-, subcritical Hopfand supercritical Hopf- biftircation. In particular, LCn occurred not only as a typical transonic flutter at the nominal dynamic pressure without any excitation but as another nonlinear transonic flutter through down to 10% lower dynamic pressure than nominal dynamic pressure by applying and removing a leading edge control surface oscillation. By changing the amplitude to control the magnitude of disturbance, unsteady limit cycle (separatrix) can be identified which separates the domain in the phase plane, one going up to LCO and the other going down to equilibrium fixed points. LCn vanished via a saddle-node bifurcation, which characterizes a subcritical Hopf bifurcation at a subcritical dynamic pressure range. LC- I also appeared by disengaging an active flutter control at around a nominal dynamic pressure and disappeared as a supercritical Hopf-bifurcation as the dynamic pressure was decreased, which suggests a possibility of changing in bifurcation nature.