Numerical simulation of transonic buffet over a supercritical airfoil

A zonal detached eddy simulation (DES) method is presented that predicts the buffet phenomenon on a supercritical airfoil at conditions very near shock buffet onset. Some issues concerning grid generation, as well as the use of DES for thin-layer separation, are discussed. The periodic motion of the shock is well reproduced by averaged Navier-Stokes equations (URANS) and zonal DES, but the URANS calculation has needed to increase the angle of attack compared to the experimental value and the standard DES failed to reproduce the self-sustained motion in the present calculation. The main features, including spectral analysis, compare favorably with experimental measurements (Jacquin, L., Molton, P., Deck, S., Maury, B., and Soulevant, D., An Experimental Study of Shock Oscillation over a Transonic Supercritical Profile, AIAA Paper 2005-4902, June 2005). A very simple model based on propagation velocities yields the main frequency of the motion. As suggested by Lee (Lee, B. H. K., Transonic Buffet on a Supercritical Airfoil, Aeronautical Journal, May 1990, pp. 143-152), this calculation highlights that upstream propagating waves are generated by the impingment of large-scale structures on the upper surface of the airfoil in the vicinity of the trailing edge. These upstream propagating waves can regenerate an instability leading to a feedback mechanism.