Computational Analysis of Hypersonic Mach Stems at High Enthalpy
Abstract
High-fidelity computational fluid dynamics simulations are imperative to understanding the complex physics of hypersonic flight. Of the many complex flow fields in hypersonic flows, Mach stems are a particular area of interest because they represent an ideal canonical flow without the added complication of walls. Simulating hypervelocity Mach stems at high enthalpy allows for studying various properties downstream of the Mach stem and gives insight into regions in the flow that are in thermochemical non-equilibrium. The University of Minnesota US3D code was paired with 5-species and 11-species air models to perform these non-equilibrium viscous computations. With such complicated physics resulting from these Mach stem simulations, several numerical phenomena had to be overcome, including volume initializations and carbuncles. The simulation results were validated using a grid convergence study, experimental schlieren overlays, and comparing downstream equilibrium properties with an in-house code. Performing simulations on the lower and upper limits of the Hypervelocity Expansion Tunnel’s (HXT) capabilities shed light on unexpected species concentrations downstream of the Mach stem. As a result, the evolution of nitric oxide concentrations downstream of the normal shock of the Mach stem was characterized using a stagnation enthalpy sweep ranging from 6.06 MJ/kg to 12.4 MJ/kg at Mach 8.5 and a Mach number sweep ranging from 5 to 11 with stagnation enthalpy 7 MJ/kg. The x-velocity, translational-rotational temperature, and atomic oxygen concentrations were also characterized in these sweeps. The rate of production/destruction of a species due to chemical reactions was calculated using two different methods, and the non-equilibrium results stemming from these two approaches were compared. Finally, a stagnation enthalpy sweep at Mach 8.5 was conducted to analyze the evolution of thermal non-equilibrium, nitric oxide chemical non-equilibrium, and atomic oxygen chemical non-equilibrium.
Subject
hypersoniccfd
computational fluid dynamics
Mach
Mach stem
Mach reflection
shear layer
turbulence
aerodynamics
non-equilibrium
chemical non-equilibrium
thermal non-equilibrium
enthalpy
Citation
Bryan, Caleb Addison (2023). Computational Analysis of Hypersonic Mach Stems at High Enthalpy. Master's thesis, Texas A&M University. Available electronically from https : / /hdl .handle .net /1969 .1 /199020.