Modeling of High-Speed Transitional and Turbulent Flows over Ablative Surfaces

Due to its significant impact on heat transfer, skin friction and aerodynamic forces, the laminar-turbulent transition process of high-speed boundary-layers will play an important role in design of NASA’s next generation hypersonic vehicles. The transition process is complex, following different paths depending on mean flow properties and the disturbance environment. This complexity is compounded by its dependence on the characteristics of the surface over which the boundary layer forms. This research proposal takes on this challenge by addressing the numerical modeling of transitional and turbulent flows over ablative surfaces in hypersonic flight regimes, an important complement to Kentucky’s established research capability for modeling and simulating Thermal Protection Systems (TPS) during high-speed atmospheric entry. Interactions between transitional/turbulent flows and surface ablation have first-order effects on the aerothermodynamic characteristics of aerospace vehicles. However, no existing simulation capability truly captures the relevant physical mechanisms involved in fully-coupled Fluid-Ablation Interactions (FAI), particularly under realistic flight conditions. Thus, transition prediction remains a significant technical challenge for a wide range of NASA applications, involving both external and internal flows. The main objective of this work is to develop a robust, efficient, and accurate simulation approach that can be used to improve hypersonic aerothermodynamic prediction capabilities, and simultaneously enhance our fundamental understanding of the coupled interactions between transitional and turbulent flows with surface ablation. To obtain accurate and efficient FAI simulation capabilities on relevant temporal and spatial scales, the proposed numerical scheme consists of five key components: (1) a nonlinear disturbance flow formulation, (2) a dual-mesh overset approach to exchange information between the baseflow and the disturbance flow solutions, (3) dynamic adaptive-mesh refinement, (4) a higher-order accurate immersed boundary method, and (5) a dynamic solid surface response model. These methods will be combined and used to simulate high-speed transitional and turbulent flows interacting with ablative surfaces, particularly the production of macroscopic distributed and discrete roughness patterns formed in the presence of transitional/turbulent flows, and to couple the influence of these surfaces, through roughness patterns and outgassing, back onto the fluid flow behavior. In order to develop an efficient simulation approach the computational performance of the solver framework will be thoroughly analyzed and optimized on modern HPC systems employing vectorization, inter-procedural optimization and multi-threading. The numerical method development will be supported by high-fidelity experiments on transitional and turbulent flow over roughened surfaces employing an advanced spatio-temporal high-resolution wave-packet tracking approach. The proposed research has the potential to be truly transformative and advance the state-of-the-art in predicting high-speed transitional and turbulent flows in the presence of ablative surfaces, as well as increase our understanding of the highly complex physics involved. If funded, the proposed research builds novel research expertise in high-speed laminar-turbulent transition at the University of Kentucky and combines it with recognized leading research in heat shield modeling. For the design of the next generation of critical TPS, reliable modeling capabilities for FAI are essential—an enabling technology for NASA’s ambitious plans for humans to go and return from the Moon, as well as for future missions to Venus, Mars and beyond.

This is a mature technology (TRL 7+) — the realistic path in is usually NASA's Technology Transfer Program: licensing an existing NASA patent, or a Space Act Agreement to use NASA facilities/expertise directly. NASA also runs a startup licensing program with no upfront fee for companies formed to commercialize a specific NASA technology.

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