A perspective on transonic buffet over an unswept finite wing

Abstract: Transonic buffet is a well-known aerodynamic instability of shock/boundary layer interaction in the transonic regime for aircraft. So far, this phenomenon has typically been investigated by modal and correlation analyses. Here, we present a perspective on low-frequency unsteadiness, of the order of St ~ O(-2), in transonic buffet, using results from temporal evolution of skin friction lines and correlation analysis on the surface of Benchmark Supercritical Wing (BSCW) with an aspect ratio AR = 2. Skin friction lines and critical point theory are well established to describe 3D separated flows based on critical points -- nodes, foci, and saddles. Dynamics of these critical points are found in a certain topology in separation regions for different angles of attack, Mach 0.85, and Reynolds number 4.491 million. The topology of critical points consists of pairs of contra-rotating unstable foci that contribute to the mechanism of formation and propagation of buffet cells -- pockets of shock foot oscillations. The dynamic nature of these critical points changes the pressure distribution on the surface, which is reflected as wave propagation in correlation plots.