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Title:Modeling of no radiative emission in non-equilibrium hypersonic flow
Author(s):Jouffray, Matthew Paul
Advisor(s):Levin, Deborah A
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Nitric Oxide
Abstract:The thermochemistry of supersonic flows has been studies thoroughly in the context of military aircraft development. Similarly, High speed hypersonic flight has been studied by both defence and civilian entities in the context of re-entry vehicles and spaceflight more generally. Hypersonic flight in regimes which causes little to no ionisation, on the other hand, are still the subject of ongoing studies. The renewed interest by high-tech nations in hypersonic weapons and vehicles has highlighted the general lack of knowledge, as well as the challenge that complex hypersonic flow thermochemistry represents. Because of compressible flow effects, the chemical reactions and non equilibrium conditions found in the shock regions of hypersonic flows have to be measured using non-invasive optical diagnostic techniques. The creation of Nitric Oxide in hypersonic shocks can be measured both by radiative emission and absorption measurements. NO is an ideal optical diagnostic tool because it has a significant absorption cross section, and is a strong emitter in the IR and the UV. The ability to model radiative emission from NO is therefore crucial to the interpretation of optical diagnostics of hypersonic air flow. This work focuses on modeling NO radiation in the UV, as well as vibrationally and electronically excited populations of NO. The conditions used for the simulations are a shock tube and a cylinder in a Hypervelocity Expansion Tube (HET) experiment. The simulated HET conditions present a 2D flow field moving around the cylinder and presents several regions of interest including the bow shock and the expansion region. Overlay techniques are applied to DSMC flow solutions in order to compute radiative emission and transport. Self normalized integrated intensity profiles are computed using the NO gamma, beta, and delta bands in the 210 nm - 250 nm region for the HET conditions for the HET case. absolute spectra radiance measurement from a shock tube is simulated, using 1D solutions from several DSMC chemistry sets. Normalized spectra in the 210 nm - 250 nm region are used to extract nonequilibrium temperature by fitting the measurements with synthetic spectra. The number density of excited species in a flow are one of the challenging parameters to compute when modeling radiative emission. A Quasi Steady state (QSS) overlay method offers an alternative to a Boltzmann calculation for the population of electronically excited species. The prediction of these electronically excited populations are necessary for the modeling of UV radiative emission. The existing collisional-radiative model is expanded with a set of reactions which provide new population mechanisms for electronically excited states of NO and N2. Although not a contributor in terms of radiation in the spectral region of interest, N2 serves as an energy reservoir capable of re-excited quenched NO molecules. The resulting population calculations are compared with Boltzmann calculations for the HET at full density and in rarefied conditions. A collisional-radiative model for vibrationally excited population analogous to the QSS model is presented. This model uses experimentally determined quenching rates for the first three vibrationally excited states of NO and the first vibrationally excited state of N2 to compute the population of these states. The computation of these states is used for modeling IR radiative emission and inform absorption experiments. The vibrational collision model is applied as an overlay to the HET DSMC solution, similarly to the QSS computation. Time resolved vibrational calculations are performed at points in the wake region of the HET domain where the residence time of the flow allows for the collisional mechanisms to produce non-Boltzmann populations. Finally, this collisional-radiative model is added to a mass transport solver to determine the first three steady state vibrational populations of NO.
Issue Date:2021-07-20
Rights Information:Copyright 2021 Matthew Jouffray
Date Available in IDEALS:2022-01-12
Date Deposited:2021-08

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