Comparative Modal Study of the Two-Dimensional and Three-Dimensional Transonic Shock Buffet

Abstract

A computational comparative study of the shock buffet phenomenon is presented. A comparison between the two-dimensional airfoil buffet and the three-dimensional swept-wing buffet is made at pre-buffet and developed buffet flow conditions to shed further light on the distinct mechanisms that characterize the phenomena. We perform modal analysis using dynamic mode decomposition and compare the dominant modal shapes and time-space evolution of the wing’s full flow field to the airfoil. This allows to characterize their distinct dominant driving mechanisms. While the airfoil buffet involves a strong interaction between the shock wave and the separated boundary layer behind it, we show that the finite-wing buffet exhibits mainly spanwise traveling perturbations that induce only small chordwise shock travel, with only weak interaction between the shock wave and boundary layer. The finite-wing shock excursion distance is significantly smaller than the airfoil’s, while the average chordwise shock wave velocities are shown to be comparable, providing a physical explanation for the swept-wing buffet frequencies that are higher than those of an airfoil.