Scrutiny of buffet mechanisms in transonic airfoils

We carry out numerical simulations of transonic flow around a supercritical airfoil at M = 0.7, incidence angle 7 deg, and Reynolds number Re = 3000000, with the aim of elucidating the mechanisms responsible for large-scale shock oscillations (buffet) which are expected to occur under these conditions. An implicit large-eddy simulation (ILES) is carried out with an upstream laminar boundary layer. Companion Reynolds-Averaged Navier-Stokes (RANS) and detached-eddy simulations (DDES) are also carried out to ascertain the feasibility of the various buffet mechanisms. Estimations of the propagation velocities of coherent disturbances and of acoustic waves are obtained, to be inserted in standard predictive models. It appears that the dynamics underlying buffet is highly localized around the mean shock location.