The test case consists in the flow over the OAT15A supercritical airfoil within the transonic buffet boundaries (Mach 0.73, Reynolds 3.10^6 and 3.5° of angle of attack). At this condition, large amplitude shock wave oscillations arise on the upper surface generating strong pressure fluctuations which can engender dangerous structural vibrations for aircraft. Similar phenomena can be found in other industrial applications such as turbomachines and air intakes. The flow was investigated in wind tunnel by Jacquin et al.  at ONERA with the main purpose of providing a welldocument test case for the CFD community. In the experiments, several unsteady pressure transducers were distributed over the airfoil and the flowfield was characterized using Schlieren cinematography and twocomponent LDV.
The transonic buffet presents a great challenge to turbulence modelling since it involves shock wave/boundary layer interaction and shockinduced separation. For these flows, due to high strain zones and strong adverse pressure gradients, standard linear eddyviscosity models seem limited. Pioneering ZonalDES computations have been performed by S. Deck (2005) and other hybrid approaches (DDES, IDDES) are worthwhile to be evaluated. Moreover, advanced URANS models and other approaches accounting for anisotropic effects (DRSM, EARSM), are expected to provide better description of the flow.
Schlieren pictures of the shock (a) most upstream and (b) most downstream locations (from Jacquin et al., 2009).
-  Jacquin et al., 2009 Experimental Study of Shock Oscillation over a Transonic Supercritical Profile, AIAA Journal, Vol. 47, No. 9, September 2009.
-  S. Deck., 2005 Numerical Simulation of Transonic Buffet over a Supercritical Airfoil; AIAA Journal, Vol. 43, No. 7, July 2005.