Author: Gan YangPublisher:
ISBN:
Category :
Languages : en
Pages :
Book Description
"Hypersonic flows over re-entry capsules are characterized by a strong bow shock with the gas seeing a rapid increase in temperature of the order of thousands of Kelvins. Chemical reactions in the resulting hot thermal non-equilibrium gas surrounding the vehicle are thus accelerated, causing ionization reactions that produce free electrons. The properties of such gas plasmas differ from those of neutral gases, causing communication blackouts. It is thus crucial to reliably predict the effects of ionization with Computational Fluid Dynamics (CFD) given its ability to produce results at all stages of the design phase at significantly reduced cost and complexity than experiments. The present work extends the capabilities of the HALO3D hypersonic flow simulation software into the weakly ionized regime, with various aspects of the physical and numerical modeling of weakly ionized flows discussed. The gasdynamic equations of chemical-thermal non-equilibrium air are solved in a loosely coupled manner to increase computational efficiency. Reactions with different controlling temperatures are modeled using laminar finite-rate chemistry, and four vibrational-electronic source terms are modeled for ionization effects. A modified Fick's law with ambipolar diffusion is implemented to account for ionized flows, with binary diffusion coefficients added to model flows at high Mach numbers. The governing equations are discretized with an edge-based stabilized finite element method (FEM) that elegantly combines the many advantages of both finite element and finite volume methods. The finite-rate chemistry solver is verified through 11-species heat baths, while the modified Fick's law accounting for ambipolar diffusion is verified against a 1-D shock tube case. The implementation of the various plasma models is then validated using flight data from the RAM C-II, while code-to-code comparisons are also performed. Finally, HALO3D's results of RAM C-II and FIRE-II vehicles using unstructured and highly anisotropic meshes are optimized using OptiGrid through a series of multi-physics criteria, ensuring verification and validation of the algorithms used"--
