Abstract: A new dynamic instability phenomenon—secondary instability flutter—is found in the study of nonlinear aeroelastic response of heated panels in supersonic flow. According to the von Karman nonlinear strain-deflection relationship, the Reissner-Mindlin plate theory, and the first order piston theory, a finite element model for the aeroelastic analysis of a heated panel in supersonic airflow is established. The nonlinear aeroelastic response of the panel is calculated numerically. The mechanism of the secondary instability flutter is not due to Hopf bifurcation, but should be interpreted by the catastrophe theory. It is also found that secondary instability flutter will not occur when the perturbed initial deflection of the panel is not large enough, and that it is affected by the initial deflection as well as the aerodynamic pressure and the temperature elevation of the panel. By applying the secondary instability flutter theory and analytical method, the flutter boundary for an aluminum panel which has been tested in a wind tunnel by other researchers is determined. The results agree well with those obtained in the wind tunnel tests. It can be concluded that the proposed secondary instability flutter theory can provide good explanation to the post-buckling thermal flutter of heated panel.

Key words: panel flutter, buckling, thermal flutter, geometric nonlinearity, catastrophe