The latest characterization of turbulent spot growth accounting for wall temperature and compressibility effects along with a formulation of the transitional Reynolds stresses are assessed in the present γ-α transition model. Additionally, previous model developments to reproduce the normal intermittency profile are now rederived based upon the exact Klebanoff profile. Furthermore, destruction and production terms of the intermittency equation are further refined assuring a more generic transition model. The construction of this transition model is primarily set up to be independent from the used turbulence model, allowing the most suitable to be selected by the user for the envisaged application. The newly developed γ-α model is validated with the classical SST turbulence model for subsonic (with and without pressure gradient) and supersonic (with and without shock wave boundary layer interaction) test cases and has shown to outperform the classical γ-Reθt model in onset location prediction, skin friction slope and overshoot.

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.

Different correlations for boundary layer transition exist within literature. However, they often require boundary layer parameters (like displacement and momentum thickness) which are not automatically provided by standard CFD tools. To tackle this problem, the boundary layer identification and transition zone detection (BLITZ) code was developed. This work presents different improvements to the tool to further extend its capabilities and improve its accuracy. To ensure faster analysis of flight vehicles, parallelization is implemented combined with a new streamline tracing and interpolation methodology. Additionally, a blending methodology between the laminar and turbulent field solution is developed based on an intermittency factor to provide a better representation of the real flow acting on the vehicle. Together with the implementation of a standalone monitoring property calculation algorithm, it is now possible to make an improved estimate of the total heat load into the vehicle as well as the aerodynamic forces exerted on it considering the evolution of the transitional flow regime. Further, improvements on the boundary layer edge detection, streamline tracing and pressure gradient calculation are implemented. The results are validated on flat plate cases with and without pressure gradient. Finally, a first validation based on launch data found in the literature is provided. Consequently, an analysis of different possible fairing geometries is given to show the impact of continuity in radius of curvature on the boundary layer transition.

As the instruments of satellites are getting more sophisticated, they are also getting more sensitive to external influences. Deposition of gases due to the low-temperature environment can be one of these external influences. For the European-Chinese SMILE mission, a Soft X-Ray Imager (SXI) is present which has CCD’s exposed to very low temperature. As water vapour is present in the air, as well as water absorbed into the paint of the enclosure, ice deposition could happen under specific conditions. To assess the outgassing of PU1 paint, an experimental outgassing study has been performed at room temperature. Additionally, numerical simulations are performed both in the continuum and the molecular regime to assess the proper functioning of the venting paths. A semi-theoretical correlation is provided which allows calculating the mass flow leaving the instrument based on the internal pressure and temperature. For the specific application of the SXI instrument, the venting rate of the enclosed air is assessed. Also, the outgassing of water vapour should not result in pressure conditions which could trigger ice deposition on the cold CCD surface. Based on the performed simulations and experiments, no issues are expected for the SXI.