Statistical Analyses of Quasiclassical Trajectory Data for Air Dissociation

Chaudhry, Ross S.; Candler, Graham V.

doi:10.2514/6.2019-0789

Cited by 25 publications

(9 citation statements)

References 44 publications

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“…In particular, it aims to complement the adaptive clustering model proposed by Sahai et al The tools adopted in this investigation include rovibrational quasi-classical trajectory (QCT) calculations , and the solution of the master equation (ME). ,, The combined use of these techniques allowed for the derivation of a novel CG strategy relying on grouping the rovibrational levels based on their energy deficit from the centrifugal barrier. The role of this quantity has been widely explored in the past, − and a detailed literature survey lies outside the scope of this paper. Only recently, however, it has been suggested to use such energy deficit as the cornerstone of a grouping strategy .…”

Section: Introductionmentioning

confidence: 99%

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O₂ + O System

et al. 2020

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This work presents an in-depth discussion on the nonequilibrium dissociation of O2 molecules colliding with O atoms, combining quasi-classical trajectory calculations, master equation, and dimensionality reduction. A rovibrationally resolved database for all of the elementary collisional processes is constructed by including all nine adiabatic electronic states of O3 in the QCT calculations. A detailed analysis of the ab initio data set reveals that for a rovibrational level, the probability of dissociating is mostly dictated by its deficit in internal energy compared to the centrifugal barrier. Because of the assumption of rotational equilibrium, the conventional vibrational-specific calculations fail to characterize such a dependence. Based on this observation, a new physics-based grouping strategy for application to coarse-grained models is proposed. By relying on a hybrid technique made of rovibrationally resolved excitation coupled to coarse-grained dissociation, the new approach is compared to the vibrational-specific model and the direct solution of the rovibrational state-to-state master equation. Simulations are performed in a zero-dimensional isothermal and isochoric chemical reactor for a wide range of temperatures (1500–20,000 K). The study shows that the main contribution to the model inadequacy of vibrational-specific approaches originates from the incapability of characterizing dissociation, rather than the energy transfers. Even when constructed with only twenty groups, the new reduced-order model outperforms the vibrational-specific one in predicting all of the QoIs related to dissociation kinetics. At the highest temperature, the accuracy in the mole fraction is improved by 2000%.

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Section: Introductionmentioning

confidence: 99%

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O₂ + O System

et al. 2020

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“…State-of-the-art models used in numerical simulations are based on limited experimental data [2][3][4] with large uncertainities. For instance, in computational fluid dynamic simulations (CFD), the widely used Park model 5 has known limitations and is not consistent with recently obtained ab-initio results [6][7][8][9][10][11][12] . In order to reduce uncertainty, ab-initio calculations using computational chemistry methods have resulted in massive amounts of data.…”

Section: Introductionmentioning

confidence: 93%

Consistent kinetic-continuum dissociation model. II. Continuum formulation and verification

Singh

Schwartzentruber

2020

The Journal of Chemical Physics

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In this article, we implement a recently developed non-equilibrium chemical kinetics model 1 based on ab initio simulation data and perform verification studies. Direct molecular simulation data is used to verify the predictive capabilities of the model. Using the model, dominant physics such as need for a rotational energy equation, and the quantitative role of non-Boltzmann effects are identified. Based on the analysis and reasonable assumptions, a simplified model for implementation into large-scale CFD simulations is proposed. Without incurring additional computational cost, the model can be used in existing flow solvers to analyze hypersonic flows.

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“…In the QSS phase, the gas has depleted internal energy distributions relative to corresponding equilibrium (Boltzmann) distribution 1,4,5 . The depletion of molecules in the high rovibrational states results in reduced dissociation rates (by a factor of 3 − 5 for nitrogen 1,15 and 2 − 5 for oxygen 16 ) relative to Boltzmann distribution based estimates 17,18 . Contrary to the depletion effects, overpopulation of high internal energy states occurs in the early phase of excitation of ro-vibrational a) Electronic mail: singh455@umn.edu.…”

Section: Introductionmentioning

confidence: 99%

Consistent Kinetic And Continuum Dissociation Models For High-Temperature Air

Singh

Schwartzentruber

2020

AIAA Scitech 2020 Forum

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In this article, we propose a generalized non-equilibrium chemical kinetics model from ab initio simulation data obtained using accurate potential energy surfaces developed recently for the purpose of studying high-temperature air chemistry. First, we present a simple cross-section model for dissociation that captures recent ab initio data accurately. The cross-section model is analytically integrated over Boltzmann distributions and general non-Boltzmann distributions to derive general non-equilibrium dissociation model. The general non-Boltzmann model systematically incorporates key physics such as dependence on translational energy, rotational energy, vibrational energy, internal energy, centrifugal barrier and non-Boltzmann effects such as overpopulation and depletion of high energy states. The model is shown to reproduce the rates from QCT for Boltzmann distributions of internal energy states. Reduced rates in non-equilibrium steady state due to depletion of high internal energy states are also predicted well by the model. Furthermore, the model predicts the enhanced rates as observed due to significant overpopulation of high vibrational states relative to Boltzmann distributions while the gas is in non-equilibrium in the transient phase. The model provides a computationally inexpensive way of incorporating non-equilibrium chemistry without incurring additional cost in the existing computational tools. Further comparisons of the model are carried out in another article, where simplifications to the model are proposed based on the results.

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Statistical Analyses of Quasiclassical Trajectory Data for Air Dissociation

Cited by 25 publications

References 44 publications

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O₂ + O System

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O₂ + O System

Consistent kinetic-continuum dissociation model. II. Continuum formulation and verification

Consistent Kinetic And Continuum Dissociation Models For High-Temperature Air

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Statistical Analyses of Quasiclassical Trajectory Data for Air Dissociation

Cited by 25 publications

References 44 publications

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O2 + O System

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O2 + O System

Consistent kinetic-continuum dissociation model. II. Continuum formulation and verification

Consistent Kinetic And Continuum Dissociation Models For High-Temperature Air

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Product

Resources

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Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O₂ + O System

Data-Inspired and Physics-Driven Model Reduction for Dissociation: Application to the O₂ + O System