Experimental investigation of the effect of steps and gaps on hypersonic vehicles

The design of hypersonic vehicles typically incorporates the use of simple, geometric shapes with smooth surfaces. There are many reasons why aircraft cannot have perfectly smooth surfaces with small, unavoidable imperfections frequently being present. These can appear in many forms, such as gaps between tiles and rivets joining different panels. Surface features like this are mainly detrimental to aircraft performance for two reasons: they can cause premature boundary layer transition, leading to higher integrated heat loads and unexpected aerodynamic loads; and they cause highly localised areas of heat flux augmentation – up to many times the undisturbed level. This work is part of a project which aims to characterise some of these effects using a combination of experimental and numerical techniques with the overall aim being to produce useful engineering level correlations for use in vehicle design. This paper presents initial experiments performed in the Oxford High Density Tunnel (HDT). Heat flux and pressure data have been acquired for a range of step and cavity geometries, and capability of a sophisticated experimental model has been shown.