Experimental Investigation of Transonic Shock Buffet on an OAT15A Profile

Self-sustained shock wave oscillations on airfoils, commonly defined as shock buffet, can occur under certain combinations of transonic Mach numbers M & INFIN; and angles of attack (AoAs) due to the interaction between the shock and the separated boundary layer. To improve the understanding of this complex phenomenon, the flow over a supercritical profile (OAT15A) was experimentally investigated for a fixed Reynolds number Rec of 3x106 and numerous aerodynamic conditions within the ranges of 2.5 deg < AoA < 6.5 deg and 0.71 < M-infinity < 0.78. Deformation and force measurements were used to assess the actual rigidity of the model and its interaction with the flow.The tracking of the shock location by means of background-oriented schlieren allowed for studying the shock featuresand the frequency content of the buffet flows. Furthermore, the inversion of shock motion and buffet onset, which arereferred to as buffet boundaries, were estimated. The inversion of shock motion proved to be a necessary but notsufficient condition for buffet onset. The trends of the results showed a good agreement with the relevant literaturecases. However, the buffet amplitude was smaller, and buffet onset occurred at considerably higher AoAs. Thecomparison of the literature results also revealed a general sensitivity of buffet features to both numerical andexperimental parameters. For this reason, the influence of the boundary-layer suction at the vertical walls and the gapflow at the side windows on the buffet features was examined. The buffet frequencies and amplitudes were slightlyaffected, but the buffet boundaries appeared to be virtually insensitive to these factors. Given the large number ofinvestigated aerodynamic conditions, these results are valuable for validation purposes of computational fluiddynamics simulations