Modal analysis of transonic buffet based on POD and DMD method

Transonic buffet is due to the self-sustained oscillations of shock wave in the unsteady transonic flow, which induces the forced periodically motion of the structure. For aircraft in transonic flow, this phenomenon exists commonly, leading to negative effects on the structural strength and fatigue life. Analysis based on mode decomposition is an effective tool for developing buffet control design. In this paper, two typical mode analysis methods, i.e., proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD), are utilized for analyzing the transonic buffet of the OAT15A airfoil. Two techniques are compared by studying the frequency of dominant modes, pressure distributions on the surface and the errors of flow construction. Results indicate that because of the consideration of frequency characteristics in DMD, the critical stable characteristics and dominant frequency of transonic buffet are well captured. Besides, DMD method accurately mimic the time evolutions of flow variables near the shock wave. Although POD method provides relatively small errors for flow reconstruction, it performs worse than DMD near the shock wave region, because of the poorer approximation of pressure evolution in time.