Experimental Investigation of Transonic Shock Buffet on an OAT15A Profile

Abstract

Self-sustained shock wave oscillations on airfoils, commonly defined as shock buffet, can occur under certain combinations of transonic Mach numbers 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 of and numerous aerodynamic conditions within the ranges of and . 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 features and the frequency content of the buffet flows. Furthermore, the inversion of shock motion and buffet onset, which are referred to as buffet boundaries, were estimated. The inversion of shock motion proved to be a necessary but not sufficient condition for buffet onset. The trends of the results showed a good agreement with the relevant literature cases. However, the buffet amplitude was smaller, and buffet onset occurred at considerably higher AoAs. The comparison of the literature results also revealed a general sensitivity of buffet features to both numerical and experimental parameters. For this reason, the influence of the boundary-layer suction at the vertical walls and the gap flow at the side windows on the buffet features was examined. The buffet frequencies and amplitudes were slightly affected, but the buffet boundaries appeared to be virtually insensitive to these factors. Given the large number of investigated aerodynamic conditions, these results are valuable for validation purposes of computational fluid dynamics simulations.