Thermal flutter prediction at trajectory points of a hypersonic vehicle based on aerothermal synchronization algorithm

Due to orders of magnitude differences in time scale between structural heat transfer and aeroelastic responses, one-way aerothermal-aeroelastic coupling is adopted to develop a thermal flutter prediction method for a hypersonic vehicle operating along a desired trajectory. In view of the strong dependency of the heat transfer process on the unsteady hypersonic trajectory, an aerothermal synchronization algorithm is established in a non-inertial frame of reference by formulating the governing equations of fluid flow and heat transfer into a unified form. Then the heated free-vibration frequencies and mode shapes are calculated at each trajectory point by using a finite-element analysis. Consequently, the flutter computations are performed on the transiently heated structure at each trajectory point by utilizing a coupled computational fluid dynamics (CFD)/computational structural dynamics (CSD) method. Because of the mass dissimilarity caused by directly increasing the dynamic pressure of a compressible flow, the technique of variable stiffness is introduced to evaluate the flutter dynamic pressure at the point of mass similarity and the stiffness margin of flutter. The present method is applied to the thermal flutter computations of a hypersonic all-movable rudder operating along a given trajectory. The computed temperature differences between the synchronization and conventional partitioned methods, and the significant effects of aerodynamic heating on the structural modes and the flutter characteristics are analyzed in detail.