At transonic flow conditions, beyond critical angles of attack the flow around airfoils exhibits shock-induced flow separation. The latter is usually accompanied with the occurrence of an aerodynamic resonance, i.e. the occurrence of initially damped aerodynamic natural oscillations of low frequency (see Fig.1). Ultimately, following a Hopf bifurcation, these flow oscillations can occasionally turn into self-excited limit cycle oscillations of large amplitude – the so calles transonic buffet or shock buffet (see Fig. 2).
The flow physics of the feedback mechanism underlying these flow oscillations, as they can be observed in wind tunnel experiments and CFD simulations, is widely unknown. Until today no adequate theory exists, that predicts frequency and damping of the natural oscillations based on the steady background flow field.