Direct Simulation Monte Carlo Dissociation Model Evaluation: Comparison to Measured Cross Sections

Wysong, Ingrid J.; Dressler, Rainer A.; Chiu, Yu‐Hui; Boyd, Iain D.

doi:10.2514/2.6655

Cited by 17 publications

(15 citation statements)

References 37 publications

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“…The TLD expressions for P¦ R have singularities at certain energies [6,2,3], giving P¦ R ¢ 1. In such cases, a single dissociation event only is performed in most DSMC codes.…”

Section: W (mentioning

confidence: 99%

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Modeling Dissociation-Vibration Coupling with the Macroscopic Chemistry Method

Lilley¹,

Macrossan²

2005

AIP Conference Proceedings

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Abstract. We test the recently developed macroscopic approach to modeling chemistry in DSMC, by simulating the flow of rarefied dissociating nitrogen over a blunt cylinder. In this macroscopic method, chemical reactions are decoupled from the collision routine. Molecules are chosen to undergo dissociation at each time step, after the collisions are calculated. The required number of reaction events is calculated from macroscopic reaction rate expressions with macroscopic information taken from the time-averaged cell properties. One advantage of this method is that "state-of-the-art" macroscopic information about reaction rates can be used directly in DSMC in the same way as in continuum codes. Hybrid Navier-Stokes/DSMC codes can therefore easily use the same chemical models in both rarefied and continuum flow regions. Here we show that the macroscopic method can capture dissociation-vibration (DV) coupling, which is an important effect in vibrationally cold blunt body flows because it results in increased surface heat fluxes. We use the macroscopic method with Park's two-temperature rate model, often used in continuum studies, to capture DV coupling in DSMC. This produces a flowfield in reasonable agreement with that calculated using the conventional collision-based threshold line dissociation model.

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“…The TLD expressions for P¦ R have singularities at certain energies [6,2,3], giving P¦ R ¢ 1. In such cases, a single dissociation event only is performed in most DSMC codes.…”

Section: W (mentioning

confidence: 99%

“…In the Monte Carlo sampling performed here to determine the TLD rates, the fraction of events with P¦ R ¢ 1 often exceeded 50%. The existence of singularities is an important limitation of the TLD model [3].…”

Section: W (mentioning

confidence: 99%

Modeling Dissociation-Vibration Coupling with the Macroscopic Chemistry Method

Lilley¹,

Macrossan²

2005

AIP Conference Proceedings

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“…Comparisons of the predictions of the TCE model and its variants for non-equilibrium calculated cross sections for exchange reactions (Dressler 2001, Chapter 3) indicates that the calculated cross sections are of the correct order, which provides some basis for optimism that the non-equilibrium predictions of the model can be considered reliable within the expected error of the method. However, caution must be exercised since detailed cross-section and rate comparisons by Wysong et al (2002) indicate that extracting adjustable parameters from measured or extrapolated equilibrium reaction rates may lead to unphysical reaction cross sections. Regardless of the ability of these methods to produce physically realistic cross sections, the fact that all these models rely on a limited database of experimental data mostly in the equilibrium regime casts doubts about their ability to cope with highly-non-equilibrium conditions successfully.…”

Section: Models Based On Arrhenius Ratesmentioning

confidence: 99%

Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

Gallis¹,

Bond²,

Torczynski³

2009

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This report summarizes the work completed during FY2009 for the LDRD project 09-1332 "Molecule-Based Approach for Computing Chemical-Reaction Rates in Upper-Atmosphere Hypersonic Flows". The goal of this project was to apply a recently proposed approach for the Direct Simulation Monte Carlo (DSMC) method to calculate chemical-reaction rates for hightemperature atmospheric species. The new DSMC model reproduces measured equilibrium reaction rates without using any macroscopic reaction-rate information. Since it uses only molecular properties, the new model is inherently able to predict reaction rates for arbitrary nonequilibrium conditions. DSMC non-equilibrium reaction rates are compared to Park's phenomenological non-equilibrium reaction-rate model, the predominant model for hypersonicflow-field calculations. For near-equilibrium conditions, Park's model is in good agreement with the DSMC-calculated reaction rates. For far-from-equilibrium conditions, corresponding to a typical shock layer, the difference between the two models can exceed 10 orders of magnitude. The DSMC predictions are also found to be in very good agreement with measured and calculated non-equilibrium reaction rates. Extensions of the model to reactions typically found in combustion flows and ionizing reactions are also found to be in very good agreement with available measurements, offering strong evidence that this is a viable and reliable technique to predict chemical reaction rates.

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“…Since there is limited information on state-specific reaction probabilities for the reactions of interest in aerodynamics, probability functions have generally been developed on a phenomenological basis and the models are calibrated to reproduce experimental reaction rates under conditions of thermal equilibrium. Validation of these models under conditions of thermal non-equilibrium has, with recent exception, generally consisted of comparisons with other DSMC simulations, rather than with experimental results [2][3][4][5] .…”

Section: Modelling Of Chemical Reactions In Dsmcmentioning

confidence: 99%

“…The expression for the fraction of high-energy collisions * F in equation [5], which is used in the rate equation [4] corresponds to the continuously distributed harmonic oscillator model for the vibrational energy levels. However, the quantized version of the vibrational energy distribution was used in the collision calculations, since this is generally considered more accurate 15 .…”

Section: A Monte Carlo Samplingmentioning

confidence: 99%

Nonequilibrium reaction rates in the macroscopic chemistry method for direct simulation Monte Carlo calculations

2007

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The Direct Simulation Monte Carlo (DSMC) method is used to simulate the flow of rarefied gases. In the Macroscopic Chemistry Method (MCM) for DSMC, chemical reaction rates calculated from local macroscopic flow properties are enforced in each cell. Unlike the standard total collision energy (TCE) chemistry model for DSMC, the new method is not restricted to an Arrhenius form of the reaction rate coefficient, nor is it restricted to a collision cross-section which yields a simple power-law viscosity.For reaction rates of interest in aerospace applications, chemically reacting collisions are generally infrequent events and, as such, local equilibrium conditions are established before a significant number of chemical reactions occur. Hence, the reaction rates which have been used in MCM have been calculated from the reaction rate data which are expected to be correct only for conditions of thermal equilibrium. Here we consider artificially high reaction rates so that the fraction of reacting collisions is not small and propose a simple method of estimating the rates of chemical reactions which can be used in the Macroscopic Chemistry Method in both equilibrium and non-equilibrium conditions.Two tests are presented: (1) The dissociation rates under conditions of thermal non-equilibrium are determined from a zero-dimensional Monte-Carlo sampling procedure which simulates 'intra-modal' non-equilibrium; that is, equilibrium distributions in each of the translational, rotational and vibrational modes but with different temperatures for each mode; (2) The 2-D hypersonic flow of molecular oxygen over a vertical plate at Mach 30 is calculated. In both cases the new method produces results in close agreement with those given by the standard TCE model in the same highly nonequilibrium conditions. We conclude that the general method of estimating the non-equilibrium reaction rate is a simple means by which information contained within non-equilibrium distribution functions predicted by the DSMC method can be included in the Macroscopic Chemistry Method.

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Direct Simulation Monte Carlo Dissociation Model Evaluation: Comparison to Measured Cross Sections

Cited by 17 publications

References 37 publications

Modeling Dissociation-Vibration Coupling with the Macroscopic Chemistry Method

Modeling Dissociation-Vibration Coupling with the Macroscopic Chemistry Method

Molecule-based approach for computing chemical-reaction rates in upper atmosphere hypersonic flows.

Nonequilibrium reaction rates in the macroscopic chemistry method for direct simulation Monte Carlo calculations

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