Investigation of the buffet characteristics of two supercritical airfoils

Abstract

The buffet characteristics of two supercritical airfoils were investigated at the high Reynolds number twodimensional test facility of the National Aeronautical Establishment. The design conditions of these two airfoils were quite similar. The thickness-to-chord ratio differed from each other by approximately 35%. The buffet onset boundaries were determined from the divergence of the unsteady balance normal force. They were compared to show the effect of thickness-to-chord ratio on buffet onset. One of the airfoils was instrumented with fast-response pressure transducers on the upper surface. Pressure intensities for shock-induced separation with reattachment as well as fully separated flows were measured. For flow conditions where discrete-frequency shock wave oscillations occurred, ensemble averaging of the unsteady pressure were carried out to determine the propagation of the pressure wave induced by periodic shock motion. Spectral analyzes of the pressure and normal force fluctuations were carried out quite deep into the buffet regime. Broadband convection velocities of the turbulent eddies were measured for fully separated flows.