Impact of transitional boundary layer evolution on slender high-speed flight vehicles

As the development of hypersonic flight vehicles is rapidly accelerating, engineers are facing different challenges through-out the design cycle. One of these challenges is the avoidance of hot spots and induced boundary layer transition. Different correlations exist that could be used by designers, but they require specific parameters such as boundary layer thickness and edge properties, streamline length, and stagnation lines, which are not directly provided by a CFD solution. To extract these specific parameters, the Boundary Layer Identification and Transition Zone Detection (BLITZ) code was further extended to extract in a fully automatic way the necessary data all around a flight vehicle and at different instances along the flight trajectory. This paper presents a comparison between purely laminar, purely turbulent and transitional flow along the flight trajectory of a slender high-speed experimental flight test vehicle with respect to boundary layer state, integrated heat load and fluxes, aerodynamic forces, critical roughness and critical steps and gaps. Based on the results obtained from this analysis, an impact assessment of the vehicle weight is performed, showing significant gross take-off weight and fuel consumption reductions when transitional parameters are used rather than a more conservative approach purely based on fully turbulent flow.