|Non-equilibrium Models for High Temperature Gas Flows|
|Doctor of Philosophy (PhD), Wright State University, 2014, Engineering PhD|
A multi-physical approach is developed for non-equilibrium high enthalpy flows to cover a wide range of interdisciplinary studies. Compressible Navier-Stokes equations are coupled with the chemical model and equation of energy conservation for internal degrees of freedom. The model is capable of accounting for the non-equilibrium dissociation and thermal radiation heat transfer in gas flows. The methodology covers a range of problems from the combustion in subsonic counter-flowing jets to the hypersonic re-entry flows. The present approach attempts to validate the finite rate chemistry mechanisms by modeling the diffusive non-premixed flame of hydrogen at a very low Mach number. The comparison with the artificial compressibility method provides some insights into the compressible Navier-Stokes equations when applied to the flow with nearly constant pressure. High Mach number flow is assessed by a TVD flux splitting scheme applied to model the re-entry of RAM-C II probe. The chemical composition of the air plasma is validated against available experimental and theoretical data. The uncertainty in electron concentration, measured by microwave reflectometers and a Langmuir probe, is examined in the light of chemical reactions, multi-temperature models, boundary conditions and a vibrational-dissociation coupling model. The heating rates are reported on a wide range of trajectory points.
A novel approach is used to improve the accuracy of the radiation transfer model based on the ray tracing method by introducing Gauss-Lobatto quadrature and space partition algorithms to the nearest neighbor search. The accuracy of the method is analyzed for hypersonic flows and for laser-supported combustion waves. The approach revealed an increased efficiency of two orders of magnitude when solving the radiation transfer energy along the line of sight. Finally, the concept of the view factor is applied to assess the radiation transfer in high temperature absorbing gas flows. This concept was verified against the ray tracing method and demonstrated several important advantages. The semi-analytical solution for the radiation flux density in axisymmetric geometry is obtained in terms of elliptic integrals. The cost of the radiation transfer model based on the view factor approach in weakly absorbing media is comparable with the cost of the tangent slab approximation and achieves the asymptotic accuracy of the ray tracing method.
Committee: George Huang, Ph.D. (Advisor); Joseph Shang, Ph.D. (Advisor); James Menart, Ph.D. (Committee Member); William Bailey, Ph.D. (Committee Member); Paul King, Ph.D. (Committee Member); Viswanath Katta, Ph.D. (Committee Member)
Aerospace Engineering; Fluid Dynamics; Mechanical Engineering
Keywords: Radiation transfer, Finite-rate chemistry, air chemistry, reentry, hypersonic flow, numerical models, gasdynamics, ray tracing method, zonal method, hydrogen combustion