Boundary Layer Transition Studies on the HEXAFLY-INT Hypersonic Glide Vehicle

The present experimental study addresses natural boundary layer transition and the effect of surface imperfections such as steps and gaps on the boundary layer state of the HEXAFLY-INT hypersonic glider. An experimental test campaign using a 1:2.6 scaled model was carried out in the High Enthalpy Shock Tunnel Gottingen (HEG) at Mach 7.4. The artificial steps and gaps on the surface are generated by means of e.g. adjustable leading edge segments which are precise scaled down elements of the flight vehicle segments. The purpose of the study is to reproduce unavoidable surface imperfections caused for instance by different thermal expansion at material junctions during flight. The experimental tests essentially helped revealing the existence of a vortex pair which after breaking down forms turbulent wedges. Until the experimental tests in HEG the existence of the vortex pair was unknown. This led to a revision of the thermal boundary conditions for the HEXAFLY-INT glider thermal analysis since the surface heat flux density in the area wetted by the turbulent wedges was found to locally increase up to five times above the laminar heat flux level.