Kinetic and Continuum Modeling of High-Temperature Air Relaxation

Abstract

Fully kinetic, vibrationally kinetic, and continuum solvers with varying model fidelity are used in this work to model the high-temperature relaxation of air in 7230 and 15,000 K adiabatic heat baths and a 6 km∕s hypersonic flow over a cylinder. The results show significant impact of uncertainties in vibrational relaxation times and reaction rate constants on thermal and chemical relaxation, in particular, on gas temperature and species mole fractions. Most notably, these uncertainties need to be reduced for collisions that include nitric oxide. Order-of-magnitude differences in the nitric oxide dissociation and recombination rates have a large impact on the peak NO mole fraction immediately behind the shock and surface-distributed heat flux, respectively. High-fidelity kinetic and continuum approaches are found to have different reaction channels having the largest effect on species mole fractions and gas temperature: N 2 O exchange and O 2 O dissociation in the former, and NO O and O 2 N 2 dissociation in the latter.

Uncertainty Quantification of Expanding High-Enthalpy Air Flows

“…Analysis of the VV relaxation times computed using the empirical expression of Klomfass (5) showed excellent agreement with recent experimental data on O 2 -N 2 VV relaxation times [20] if the factor KV V cd was taken to be equal to 4 (in the original work of Klomfass it is equal to 1). Thus, in the present study, KV V cd was assumed to be uniformly distributed between 3 and 5, which corresponds to a 25% uncertainty in the VV relaxation times, this is comparable to the 30%-40% experimental uncertainty reported by Streicher et al [20].…”

“…In shock tunnel facilities, such as the High Enthalpy Shock Tunnel Göttingen (HEG) [7], the flow is stagnated in order to achieve the required enthalpies; as it then expands through a nozzle section, thermochemical relaxation and subsequent freezing of the flow takes place, potentially leading to a chemically and vibrationally non-equilibrium flow at the nozzle exit [2]. The modeling of hypersonic flows is complicated by significant uncertainties in the data on the thermochemical relaxation rates, as well as the often significant impact on the choice of models to describe the relaxation processes [10,18,5,6].…”

Transport Cross Sections and Collision Integrals for O($$^{3}$$P)–O($$^{3}$$P) Interaction

“…The excited states PECs of the oxygen molecule are needed [20,21]. This study reports the PECs dissociating to the ground state atoms but the interaction of excited atoms poses a challenge which only recenltly have been addressed by one study [22].…”

Numerical Research for Hypersonic 3D Flow with High-Temperature Effect and Catalytic Conditions

“…Therefore physical-chemical processes can be strong enough to influence and even dominate the flow characters in the high-temperature region. The question and mechanism arouse many authors' interest [1][2][3][4][5] . The combination of kinetic energy and high speed is transformed into high air temperature and endothermal chemical processes (Figure 1), including the ionization and dissociation of atmospheric species in the high-temperature region.…”