Towards a Strand-Cartesian Solver for Modelling Hypersonic Flows in Thermochemical Non-Equilibrium

Abstract

The extreme conditions experienced in hypersonic flight can be difficult to reproduce in ground test facilities. As such, the use of computational simulations is vital in the design of Thermal Protection Systems (TPSs) for hypersonic vehicles. A relatively recent paradigm within Computational Fluid Dynamics (CFD) is to discretise the space around a vehicle using the strand/Cartesian Adaptive Mesh Refinement (AMR) technique, which requires minimal user input, with much of the process automated. This techniques combines a strand'' mesh, grown from a discretised surface, in the near-body region with an adaptive Cartesian mesh in the off-body region. This technique could be useful in the assessment of TPSs, where ablating surfaces and flexible TPSs require the mesh to be updated as the shape of the body changes. To this end, a prototype strand/Cartesian AMR solver has been created using the AMROC (Adaptive Mesh Refinement in Object-oriented C++) framework. A patch integrator within AMROC has been extended to include Park's two-temperature model in order to model the thermochemical nonequilibrium present in hypersonic flows. A mapped spatial integration scheme has been developed along with strand meshing techniques in order to discretise the near-body domain using an input surface. Overset algorithms have been implemented to join the domains. The design of off-body and near-body solvers and the overset algorithms are presented along with a series of test cases that aim to verify and validate the hypersonic 2D/axisymmetric strand/Cartesian AMR solver. Shocktube results are compared with those from the literature, and code-to-code comparisons are carried out. The hypersonic model is validated using comparisons with Lobb's hypersonic sphere experiments, and the heat flux results are validated using data from a high-enthalpy shock tunnel experiment. The results indicate that the strand/Cartesian AMR technique could be used to accurately simulate vehicles in hypersonic flows.