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  • 1
    Electronic Resource
    Electronic Resource
    Thermal rate constants of the O2+N→NO+O reaction based on the A〈sup LOCATION="PRE"〉2′ and A〈sup LOCATION="PRE"〉4′ potential-energy surfaces (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 6136-6145 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A detailed quasiclassical trajectory study of the O2+N→NO+O reaction is performed based on ab initio potential-energy surfaces of the 2A′ and 4A′ states. The study is aimed at generating a database of thermally averaged and O2 state-specific rate constants needed for accurate simulations of NO kinetics in high-temperature flow processes. The rate constants obtained show good agreement with the available experimental data and with other quasiclassical trajectory calculations. It is found that the reactant internal energy of the O2+N→NO+O reaction is less effective in enhancing the rate than in theN2+O→NO+N reaction. An analysis of the product vibrational energy shows that NO formed by theO2+N→NO+O reaction has a non-Boltzmann distribution. It is also found that the most populated NO vibrational level is determined by the reactant vibrational energy, while the terminal slope of the NO vibrational distribution is a strong function of the reactant translational temperature. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475132
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  • 2
    Electronic Resource
    Electronic Resource
    Thermal rate constants of the N2+O→NO+N reaction using ab initio 3A″ and 3A′ potential energy surfaces (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 2825-2833 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Theoretical determinations of the thermal rate constants and product energy distributions of the N2+O→NO+N reaction, which plays a crucial role in hydrocarbon air combustion and high temperature air chemistry, are carried out using a quasiclassical trajectory method. An analytical fit of the lowest 3A′ potential energy surface of this reaction based on the CCI ab initio data is obtained. The trajectory study is done on this surface and an analytical 3A″ surface proposed by Gilibert et al. [J. Chem. Phys. 97, 5542 (1992)]. The thermal rate constants computed from 3000 to 20 000 K are in good agreement with the available experimental data. In addition, the dependence of the rate constant on the N2 internal state is studied. It is found that a low vibrational excitation can reduce the rate constant of this reaction by a factor of 3. Also, we investigate the effect of the N2 vibrational state on the product NO vibrational distribution, and it is found that at low N2 vibrational states, the NO vibrational distribution is nearly Boltzmann. However, at N2(v(approximately-greater-than)10), the product distribution is almost uniform at low energy levels. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471106
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  • 3
    Electronic Resource
    Electronic Resource
    Detailed simulation of nitrogen dissociation in stagnation regions (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 2108-2117 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vibrational relaxation rates from Schwartz–Slawsky–Herzfeld theory and the forced-harmonic oscillator model are used to study the flow of nitrogen in the stagnation region of a blunt body. The mass conservation equations are coupled to the momentum and total energy equations, and solved using an implicit finite-volume computational fluid dynamics method. The effects of single- and multiple-quantum vibration–translation transitions and vibration–vibration transitions are studied. Also, the effect of the mass diffusion of the excited oscillators across the shock layer is investigated. It is found that highly non-Boltzmann vibrational distributions are present in the flow field, and that the forced-harmonic oscillator model predicts that dissociation occurs from the low vibrational levels only. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869330
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  • 4
    Electronic Resource
    Electronic Resource
    Vibrational energy conservation with vibration–dissociation coupling: General theory and numerical studies (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 1764-1774 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coupling between vibrational relaxation and dissociation in nitrogen is studied. The conservation of vibrational energy equation is derived and the form of the source terms is determined for physically consistent coupling models. Using a computational fluid dynamics method, the results from three current coupling models are compared to existing experimental interferograms for spherical geometries. It is found that the coupling models of Park, Treanor and Marrone, and Macheret and Rich are able to accurately predict the shock standoff distances and reproduce the experimental interference patterns for these conditions. However, there are differences in the vibrational temperature profiles among the coupling models. The experimental interferograms are not sensitive to these differences, though. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868491
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  • 5
    Electronic Resource
    Electronic Resource
    A multiple translational temperature gas dynamics model (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 6 (1994), S. 3776-3786 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Within shock waves, the translational motion of the gas is more energetic in the direction perpendicular to the shock than in the direction parallel to the shock. To represent this translational nonequilibrium, new continuum conservation equations are developed. These equations are derived by solving the Boltzmann equation with a first-order Chapman–Enskog expansion of an anisotropic velocity distribution function. This results in a gas model with anisotropic pressure, temperature, and speed of sound. The governing equations are solved numerically for one-dimensional steady shock waves in a Maxwellian gas. The numerical results are compared to those obtained using the direct simulation Monte Carlo method. The new continuum model captures many of the features of shock waves. In particular, this paper finds that translational nonequilibrium is present at all Mach numbers. For Mach numbers greater than 1.5, the perpendicular temperature overshoots the post-shock temperature. At the point where this temperature reaches a maximum, the model predicts that for any shock wave, the square of the perpendicular-direction Mach number is one-third; this is substantiated by the DSMC results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868367
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  • 6
    Electronic Resource
    Electronic Resource
    Effect of chemical reactions on decaying isotropic turbulence (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 1715-1724 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: There have been many studies of turbulent combustion flows, however the interaction between turbulent motion and the chemical reactions that occur in hypersonic flows has not been studied. In these flows, the rate of product formation depends almost exclusively on the temperature, and small temperature fluctuations may produce large changes in the rate of product formation. To study this process, we perform direct numerical simulations of reacting isotropic turbulence decay under conditions typical of a hypersonic turbulent boundary layer flow. We find that there is a positive feedback between the turbulence and exothermic reactions. That is, positive temperature fluctuations increase the reaction rate, thereby increasing the heat released by the reaction, which further increases the temperature. Simultaneously, the pressure increases causing localized expansions and compressions that feed the turbulent kinetic energy. The Reynolds stress budget shows that the feedback occurs through the pressure-strain term. We also find that the strength of the feedback depends on how much heat is released, the rate at which it is released, and the turbulent Mach number. The feedback process is negative for endothermic reactions, and temperature fluctuations are damped. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869688
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of hypersonic flows using a detailed nitric oxide formation model (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 9 (1997), S. 1171-1181 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: In this paper the extensive quasiclassical trajectory (QCT) study recently concluded [J. Chem. Phys. 104, 2825 (1996)] is used to model the kinetics of the primary NO formation reaction, N2+O→NO+N, in hypersonic nonequilibrium flows. The QCT data are used to obtain expressions for the thermal rate constant, reactant energy removal, and product energy disposal rates of this reaction. The QCT results are coupled with the continuum conservation flow equations, and these equations are used to simulate the Bow-Shock UltraViolet2 (BSUV2) flow at altitudes between 75 to 87.5 km. It is found that the use of the Macheret and Rich [Chem. Phys. 174, 25 (1993)] vibration–dissociation coupling model along with the QCT rates gives improvements in the NO concentration predictions at altitudes between 80 and 85 km. Also, it is found that the vibrational and rotational temperatures of NO are much higher than that of the N2 and O2 in the gas, in accordance with the BSUV2 measurements. The amount of NO produced in the flow fields at 87.5 km and above is found to be strongly dependent on the free-stream density of atomic oxygen. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869205
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  • 8
    Electronic Resource
    Electronic Resource
    Subgrid-scale model for the temperature fluctuations in reacting hypersonic turbulent flows (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 11 (1999), S. 2765-2771 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A direct numerical simulation (DNS) database is used to develop a model of subgrid-scale temperature fluctuations for use in large-eddy simulations of turbulent, reacting hypersonic flows. The proposed model uses a probability density representation of the temperature fluctuations. The DNS database reveals a physically consistent relation between the resolved-scale flow conditions that may be used to predict the standard deviation of the Gaussian probability density function (PDF). The model is calibrated and tested by comparison to simulations of decaying isotropic turbulence. The conditional single-variable PDF model is found to capture the fluctuations in temperature and product formation. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870135
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  • 9
    Electronic Resource
    Electronic Resource
    Dissociation modeling in low density hypersonic flows of air (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 7 (1995), S. 1757-1763 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vibration–dissociation coupling in low-density, hypersonic flows of air is investigated. Radiative emission data for nitric oxide and for atomic oxygen measured by a reentry flight experiment are used to assess the modeling of this phenomenon. Flow field computations are performed using the direct simulation Monte Carlo method. Due to the relatively small number of collisions under high-altitude, low-density flow conditions, an overlay approach is used to simulate changes in chemical composition of trace species, including both nitric oxide and atomic oxygen. Radiative emission is calculated using a nonequilibrium radiation method. It is found that the strong degree of thermal nonequilibrium that occurs in high-altitude, hypersonic flows makes the chemistry very sensitive to the vibration–dissociation coupling model. A number of such models based on continuum and particle representations of the flow are assessed. A variation in dissociation rate of up to nine orders of magnitude among these models is found for the lowest-density flight conditions. By using a sophisticated dissociation model, the emission calculated at the highest altitude for which measurements are available is improved from a factor of 220 too low to within a factor of 4 too low. With the same model, improvement by a factor of 50 is also obtained for the computation of emission from atomic oxygen. This is the first time that the observed dependence of the flight data on the free-stream density has been predicted correctly. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.868490
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  • 10
    Electronic Resource
    Electronic Resource
    Numerical study of hypersonic reacting boundary layer transition on cones (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 10 (1998), S. 2676-2685 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hypersonic gas flow over cones is solved using computational fluid dynamics to obtain accurate boundary layer profiles. A linear stability analysis is performed on the profiles to determine the amplification rates of naturally occurring disturbances, and this information is used with the eN method to predict the boundary layer transition location. The effects of free-stream total enthalpy and chemical composition on transition location are studied to give a better understanding of recent experimental observations. Namely, there is an increase in transition Reynolds number with increasing free-stream total enthalpy, and this increase is greater for gases with lower dissociation energies. The results show that linear stability predicts the same trends that were observed in the experiments, but with N=10, it consistently overpredicts the transition Reynolds numbers by about a factor of 2. The results of numerical experiments are presented which show the effect of reaction endo- or exothermicity on disturbance amplification rates. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.869781
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