Coarse-grain cross sections for rovibrational excitation and dissociation of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si58.svg"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">N</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo linebreak="badbreak">-</mml:mo><mml:mi mathvariant="normal">N</mml:mi></mml:mrow></mml:math> system

Torres, Erik; Jaffe, Richard L.; Schwenke, David W.; Magin, Thierry

doi:10.1016/j.chemphys.2020.110701

Cited by 3 publications

(2 citation statements)

References 62 publications

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“…Both are subject to it but in different ways. In the StS-ME approach, statistical noise is most apparent during the generation of the QCT database and can best be observed when examining individual cross sections. , In broad terms, each state-to-state rate coefficient for a particular elementary process is obtained based on a large but finite number of QCT calculations. The initial conditions for these calculations must be randomly sampled from prescribed distributions of initial collision energies, impact parameters, and so forth, and the final rate coefficient for each elementary process is determined from a small subset of the simulated trajectories.…”

Section: Computational Detailsmentioning

confidence: 99%

“…This includes vibrational StS-ME studies of the O 2 –O , and O 2 –O 2 systems, combined oxygen systems, and N 2 –N, − N 2 –N 2 , , N–O 2 , and N 2 –O 2 systems. In addition, efforts have been made to construct reduced-order models based on ab initio PESs using a coarse-grain method on internal energy states. ,,− …”

Section: Introductionmentioning

confidence: 99%

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State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N₂–N System

et al. 2020

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We present a detailed comparison of two high-fidelity approaches for simulating non-equilibrium chemical processes in gases: the state-to-state master equation (StS-ME) and the direct molecular simulation (DMS) methods. The former is a deterministic method, which relies on the pre-computed kinetic database for the N2–N system based on the NASA Ames ab initio potential energy surface (PES) to describe the evolution of the molecules’ internal energy states through a system of master equations. The latter is a stochastic interpretation of molecular dynamics relying exclusively on the same ab initio PES. It directly tracks the microscopic gas state through a particle ensemble undergoing a sequence of collisions. We study a mixture of nitrogen molecules and atoms forced into strong thermochemical non-equilibrium by sudden exposure of rovibrationally cold gas to a high-temperature heat bath. We observe excellent agreement between the DMS and StS-ME predictions for the transfer rates of translational into rotational and vibrational energy, as well as of dissociation rates across a wide range of temperatures. Both methods agree down to the microscopic scale, where they predict the same non-Boltzmann population distributions during quasi-steady-state dissociation. Beyond establishing the equivalence of both methods, this cross-validation helped in reinterpreting the NASA Ames kinetic database and resolve discrepancies observed in prior studies. The close agreement found between the StS-ME and DMS methods, whose sole model inputs are the PESs, lends confidence to their use as benchmark tools for studying high-temperature air chemistry.

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Section: Computational Detailsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N₂–N System

et al. 2020

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Rovibrationally state-specific collision model for the O2(Σg−3) + O(P3) system in DSMC

Pan

Stephani

2021

The Journal of Chemical Physics

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A rovibrationally state-specific collision model for the O2(Σg−3)+O(P3) system is presented for direct simulation Monte Carlo, including rotation–vibration–translation energy transfer, exchange, dissociation, and recombination processes. The two-step binary collision approach is employed to model recombination reactions. Two available cross section databases by Andrienko/Boyd and Esposito/Capitelli are employed for the rovibrationally resolved model (rv-STS) and vibrationally resolved model (v-STS), respectively. The difference between rv-STS and v-STS comes from two contributions: the multisurface factor of dissociation (fMS) and the rotational averaging process. The dissociation cross section with the constant fMS is typically larger than with the variable fMS, especially for the low vibrational energy states. On the other hand, the cross sections resulting from the rotationally averaged database are found to underpredict the dissociation rate coefficient at low temperatures. In the rovibrational heating case, the rv-STS predicts faster relaxation than the v-STS, which also shows a lower quasi-steady-state temperature than v-STS. In the rovibrational cooling case, the rv-STS shows a faster relaxation than v-STS, which also presents a thermal non-equilibrium between rovibrational and translational mode during the cooling process.

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How to build coarse-grain transport models consistent from the kinetic to fluid regimes

2021

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In this paper, we examine how to build coarse-grain transport models consistently from the kinetic to fluid regimes. The internal energy of the gas particles is described through a state-to-state approach. A kinetic equation allows us to study transport phenomena in phase space for a non-homogeneous gas mixture. Internal energy excitation is modeled using a binary collision operator, whereas gas chemical processes rely on a reactive collision operator. We obtain an asymptotic fluid model by means of a Chapman–Enskog perturbative solution to the Boltzmann equation in the Maxwellian reaction regime. The macroscopic conservation equations of species mass, mixture momentum, and energy as well as expressions of the transport properties are given. Reversibility relations for elementary processes are formulated in the coarse-grain model at the kinetic level and are enforced in the collision algorithm of the direct simulation Monte Carlo method used to solve the kinetic equation. Furthermore, respecting these reversibility relations is key to deriving a fluid model that is well-posed and compatible with the second law of thermodynamics. The consistency between the kinetic and fluid simulations is assessed for the simulation of a shock wave in a nitrogen gas using the uniform rovibrational collisional coarse-grain model. The kinetic and fluid simulations show consistency for the macroscopic properties and transport fluxes between both regimes.

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Coarse-grain cross sections for rovibrational excitation and dissociation of the N2-N system

Cited by 3 publications

References 62 publications

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N₂–N System

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N₂–N System

Rovibrationally state-specific collision model for the O2(Σg−3) + O(P3) system in DSMC

How to build coarse-grain transport models consistent from the kinetic to fluid regimes

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Coarse-grain cross sections for rovibrational excitation and dissociation of the N2-N system

Cited by 3 publications

References 62 publications

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N2–N System

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N2–N System

Rovibrationally state-specific collision model for the O2(Σg−3) + O(P3) system in DSMC

How to build coarse-grain transport models consistent from the kinetic to fluid regimes

Contact Info

Product

Resources

About

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N₂–N System

State-to-State Master Equation and Direct Molecular Simulation Study of Energy Transfer and Dissociation for the N₂–N System