21st Congress of International Council of the Aeronautical Sciences, Melbourne, Australia, 13-18 September, 1998
Paper ICAS-98-4.1.2

NONLINEAR CHARACTERISTICS OF TRANSONIC FLUTTER OF A HIGH ASPECT RATIO WING

Matsushita H., Saitoh K., Granasy P.*
National Aerospace Laboratory, Japan; *GE Lighting Europe, Hungary

Keywords: nonlinear, transonic flutter, high aspect ratio wing

Wind tunnel model of a high aspect ratio wing for active flutter control study enters flutter of limit cycle oscillation (LCO) type. In order to get better understanding and mathematically modeling the transonic flutter for active control, wind tunnel tests were conducted. During the tests, a typical nonlinear dynamics emerged; a nominal flutter without any intentional excitation occurred as a large amplitude limit cycle oscillation (LC-II) via a subcritical Hopf bifurcation in conjunction with saddle-node bifurcation, while a small amplitude limit cycle oscillation (LC-I ) appeared as a supercritical Hopf bifurcation. In particular, LC-II occurred at well below the nominal flutter dynamic pressure if the wing was excited by a leading edge control surface. This limit cycle oscillation remained stable until almost 10% lower dynamic pressure than nominal value where LCO vanished via a saddle-node bifurcation. Quantitative bifurcation diagram was thus obtained by the test and an empirical math model of single degree-of-freedom is proposed. Furthermore, LC-I was realized by disengaging a flutter control at a slightly higher dynamic pressure than nominal value. As the dynamic pressure was further decreased, this LC-I disappeared in a supercritical Hopf-bifurcation. This paper analyzes these new findings obtained in the tests by the nonlinear dynamics framework.

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