KY EPSCoR: FY21: NASA: Research Area (RA) State Match: Modeling of High-Speed Transitional and Turbulent Flows over Ablative Surfaces - Science - Match for 3200002702

In the design of NASA’s next generation hypersonic aerospace vehicles the laminar-turbulent boundary-layer transition process plays a central role because the state of the high-speed boundary-layer, i.e. laminar, transitional, or turbulent, can have a strong effect on skin friction and heat transfer as well as aerodynamic lift and moments. The transition process is complex and can follow different paths depending on mean flow properties, the disturbance environment, and characteristics of the abutting solid surface, which greatly complicates accurate prediction of transitional flows. This research proposal aims at modeling transitional and turbulent flows over complex surfaces in hypersonic flight regimes, an important complement to Kentucky’s established research capability for modeling and simulating ablative surfaces during high-speed atmospheric entry. Even though it is well-known that interactions between transitional/turbulent flows and surface ablation can have first-order effects on the aerothermodynamic characteristics of aerospace vehicles, as yet there is no sophisticated simulation capability available that can truly capture the relevant physical mechanisms involved in fully-coupled Fluid-Ablation Interactions, particularly under realistic hypersonic flow conditions. Thus, transition mechanisms that are relevant to a wide range of NASA applications involving both external and internal flows are currently poorly understood. Here in Kentucky, we have the opportunity to build a novel research expertise in hypersonic laminar-turbulent transition and combine it with recognized leading research in ablative surface modeling. For the design of the next generation of critical Thermal Protection Systems, reliable modeling capabilities for fluid-ablation interaction are essential — an enabling technology for NASA’s ambitious plans for humans to go and return from the Moon, as well as to conduct missions to Mars and beyond. 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 in general, and enhance our understanding of the coupled interactions between transitional and turbulent flows with surface ablation as a specific demonstration example. To achieve accurate and efficient simulations capturing fluid-solid interactions on relevant temporal and spatial scales, the proposed approach 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) adaptive-mesh refinement, (4) a higher-order accurate immersed boundary method, and (5) a dynamic solid surface response model. These methods will be used to simulate high-speed transitional and turbulent flows interacting with ablative surfaces, including 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, outgassing, etc., back onto the fluid flow behavior. The numerical method development will be supported by high-fidelity experiments on transitional and turbulent flow over roughened surfaces employing an advanced wave-packet tracking approach. The proposed research has the potential to advance the state-of-the-art in predicting high-speed transitional and turbulent flows in the presence of ablative surfaces, and increase our understanding of the highly complex physics involved. • Mission Directorate(s)/Centers Alignment: Active collaboration and interactions are planned with NASA-ARC, NASA-LaRC, NASA-JSC and aerospace industry partners. The research is relevant to AMD, STMD, and HEOMD. • Areas of expertise required for the research: Computational and experimental fluid dynamics, laminar-turbulent transition, turbulence, and surface ablation. • Science-I: Dr. Christoph Brehm