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The University of Southampton

Research project: Automated Mesh Generation for Hypersonic Flow Simulations of Ablated Bodies

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Strand/Cartesian AMR meshes applied to surface motion problems

Vehicles travelling at hypersonic speeds experience significant heat transfer from the surrounding flow. This can require the use of thermal protection systems that ablate at high temperatures to reduce the heating experienced by the vehicle. Ablation leads to shape change, which can cause bottlenecks in computational simulations as a new computational mesh is required. This project is investigating the use of strand/Cartesian AMR meshing procedures to automatically create high-quality grids around ablating bodies.

Cartesian Adaptive Mesh Refinement (AMR) and strand mesh algorithms are two largely automated procedures that can be used to discretise the computational domain in fluid simulations.

Cartesian AMR algorithms are able to resolve important flow features in an automated and efficient manner. This is achieved through mesh refinement in areas of interest, such as where there are high gradients or large discretisation errors. However, the Cartesian structure often leads to approximations in the surface geometry, which can distort the boundary layer and lead to inaccuracies in surface results (heat flux, shear stress).

Strand mesh algorithms create a mesh by growing strands from an arbitrary surface and then joining nodes on the strands to make computational cells. Strand meshes can accurately represent a surface geometry and can incorporate stretching in the wall normal direction to improve the accuracy of surface results for a set number of cells. However, the strand mesh cannot resolve flow features automatically and there are limitations to how far from the surface the strands can grow, for example when strands cross.

The advantages of the two meshing paradigms can be combined using overset (a.k.a. Chimera) meshing techniques to join a near-body strand mesh with an off-body Cartesian AMR mesh. Overset algorithms enable separate computational domains to be joined together using boundary conditions. The boundary conditions from one domain are set using interpolated data from another domain. The combination of the two meshes enables meshes to be automatically created that highly resolve off-body flow features and boundary layer flows.

In this research, the AMROC Cartesian AMR framework has been extended to include a hypersonic fluid model (two-temperature model). The Cartesian solver has been adapted to enable the use of body-fitted meshes that can be created using strand generation algorithms. Overset methods have been implemented to enable efficient, parallel point-to-point communication between overset meshes, utilising existing features of the AMROC framework where possible. The overset strand/Cartesian AMR solver has been validated using experimental heat flux results and the automated meshing procedure has been demonstrated using a range of geometries.   

Shock resolution and surface representation with an AMR mesh.
Shock resolution and surface representation with an AMR mesh
Shock resolution and surface representation with a strand mesh
Shock resolution and surface representation with a strand mesh
Shock resolution and surface representation with an overset strand/Cartesian AMR mesh
Shock resolution and surface representation with overset strand mesh
Demonstration of heat flux results when using a strand/Cartesian AMR mesh around an ablated body.
Demonstration of heat flux results when using a strand mesh

Related research groups

Aerodynamics and Flight Mechanics

Key Publications

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