The Experts below are selected from a list of 213 Experts worldwide ranked by ideXlab platform
Anouar Soufiani - One of the best experts on this subject based on the ideXlab platform.
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Flow-radiation coupling for atmospheric entries using a Hybrid Statistical Narrow Band Model
Journal of Quantitative Spectroscopy and Radiative Transfer, 2016Co-Authors: Laurent Soucasse, Philippe Riviere, James B. Scoggins, Thierry E. Magin, Anouar SoufianiAbstract:In this study, a Hybrid Statistical Narrow Band (HSNB) Model is implemented to make fast and accurate predictions of radiative transfer effects on hypersonic entry flows. The HSNB Model combines a Statistical Narrow Band (SNB) Model for optically thick molecular systems, a box Model for optically thin molecular systems and continua, and a Line-By Line (LBL) description of atomic radiation. Radiative transfer calculations are coupled to a 1D stagnation-line flow Model under thermal and chemical nonequilibrium. Earth entry conditions corresponding to the FIRE 2 experiment, as well as Titan entry conditions corresponding to the Huygens probe, are considered in this work. Thermal nonequilibrium is described by a two temperature Model, although non-Boltzmann distributions of electronic levels provided by a Quasi-Steady State Model are also considered for radiative transfer. For all the studied configurations, radiative transfer effects on the flow, the plasma chemistry and the total heat flux at the wall are analyzed in detail. The HSNB Model is shown to reproduce LBL results with an accuracy better than 5% and a speed up of the computational time around two orders of magnitude. Concerning molecular radiation, the HSNB Model provides a significant improvement in accuracy compared to the Smeared-Rotational-Band Model, especially for Titan entries dominated by optically thick CN radiation. (C) 2016 Elsevier Ltd. All rights reserved.
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Coupled Flow, Radiation, and Ablation Simulations of Atmospheric Entry Vehicles using the Hybrid Statistical Narrow Band Model
45th AIAA Thermophysics Conference, 2015Co-Authors: James B. Scoggins, Philippe Riviere, Anouar Soufiani, Laurent Soucasse, Thierry MaginAbstract:A Model for coupled flow, radiation, and ablation calculations along the stagnation lines of atmospheric entry vehicles is developed to study the effects these coupled phenomena have on each other as well as the predicted quantities of interest to vehicle designers. The flow Model is based on the two-temperature, multicomponent, reacting Navier-Stokes equations coupled to radiative heat and photochemistry source terms and reduced to onedimension using the dimensionally reduced Navier-Stokes approximation. The radiative source terms are computed using the hybrid statistical narrow Band Model developed at the EM2C laboratory at Ecole Centrale Paris. This Model has previously been shown to accurately produce radiative properties at significantly reduced computational cost when compared to line-by-line calculations for uncoupled flows without ablation. In this work, the hybrid statistical narrow Band Model is coupled to the one-dimensional stagnation line flow solver with ablation. Ablation is treated through a simple steady-state ablation boundary condition with finite-rate heterogenous reactions capable of simulating ablation products blowing into the boundary layer. The Model is first used to simulate the effect of carbonaceous species in a typical boundary layer environment. In particular, it is shown that a boundary layer contaminated with a relatively small amount of ablation and pyrolysis products can have significantly lower transmissivities than a boundary layer with pure air. Finally, the peak heating point for the Apollo 4 command module is analyzed using each of the four possible coupling strategies: flow, flow and ablation, flow and radiation, and fully coupled. It is shown that for this case, radiation coupling is the dominant phenomena due to a relatively small carbon yield in the boundary layer. In addition, comparison of cumulative intensities with the radiometer measurement made during the flight shows excellent agreement and confirms the assumption that the radiometer cavity has little effect on the measured intensity due to the low amount of carbon present in the cavity.
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updated Band Model parameters for h2o co2 ch4 and co radiation at high temperature
International Journal of Heat and Mass Transfer, 2012Co-Authors: Philippe Riviere, Anouar SoufianiAbstract:Abstract Statistical narrow-Band (SNB) Model parameters for H2O, CO2, CH4 and CO, and correlated-k (CK) parameters for H2O and CO2 are generated from line by line calculations and recently improved spectroscopic databases in wide temperature and spectral ranges. Results from the new parameters are compared to direct line by line calculations and to results from earlier Model parameters [A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-Band Model for H2O, CO2 and CO and correlated-k (ck) Model for H2O and CO2, Int. J. Heat Mass Transfer 40 (1997) 987–991] in terms of Band averaged spectral transmissivities, Planck mean absorption coefficients, and total emissivities. The comparisons show first a good agreement between updated SNB, CK and LBL results. Significant improvements on earlier parameters are observed for H2O and CO2, especially at very high temperatures and path lengths. Model parameters and computer programs illustrating their implementation are provided as Supplementary data .
Georges Bouzerar - One of the best experts on this subject based on the ideXlab platform.
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First Principle Investigation on Thermoelectric Properties of Transition Metal Dichalcogenides: Beyond the Rigid Band Model
Journal of Physical Chemistry C, 2017Co-Authors: Christophe Adessi, S. Thebaud, R. Bouzerar, Georges BouzerarAbstract:The thermoelectric properties (electrical conductivity, Seebeck coefficient, and power factor) of single layer transition metal dichalcogenides (MoS2, MoSe2, WS2, and WSe2) are investigated theoretically on the basis of ab initio quantum transport using the Landauer Büttiker formalism. The often used rigid Band Model is compared to realistic doping, namely substitution and adsorption, it is found that several important physical insights governing the transport are missing in this approximation. The rigid Band Model appears to clearly overestimate the thermoelectic efficiency, hampering its relevance for thermoelectric studies. Substitution doping by chloride or phosphorus leads to poor power factor due to drastic changes of the pristine Band structure. In contrast, adsorption doping by alkalies (Li, Na, K, and Rb) favors larger power factor. Realistic treatment of the disorder induced by the dopants is also investigated and reveals that Cl doping leads to very short localization length of 3.5 nm while K comes with micrometer length scale. The Anderson localization phenomenon in thermoelectric properties of single layer transition metal dichalcogenides definitely comes out as a main issue.
F M Peeters - One of the best experts on this subject based on the ideXlab platform.
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excitons and trions in monolayer transition metal dichalcogenides a comparative study between the multiBand Model and the quadratic single Band Model
Physical Review B, 2017Co-Authors: M Van Der Donck, M Zarenia, F M PeetersAbstract:The electronic and structural properties of excitons and trions in monolayer transition metal dichalcogenides are investigated using both a multiBand and a single-Band Model. In the multiBand Model we construct the excitonic Hamiltonian in the product base of the single-particle states at the conduction and valence Band edges. We decouple the corresponding energy eigenvalue equation and solve the resulting differential equation self-consistently, using the finite element method (FEM), to determine the energy eigenvalues and the wave functions. As a comparison, we also consider the simple single-Band Model which is often used in numerical studies. We solve the energy eigenvalue equation using the FEM as well as with the stochastic variational method (SVM) in which a variational wave function is expanded in a basis of a large number of correlated Gaussians. We find good agreement between the results of both methods, as well as with other theoretical works for excitons, and we also compare with available experimental data. For trions the agreement between both methods is not as good due to our neglect of angular correlations when using the FEM. Finally, when comparing the two Models, we see that the presence of the valence Bands in the mutiBand Model leads to differences with the single-Band Model when (interBand) interactions are strong.
Laurent Soucasse - One of the best experts on this subject based on the ideXlab platform.
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Flow-radiation coupling for atmospheric entries using a Hybrid Statistical Narrow Band Model
Journal of Quantitative Spectroscopy and Radiative Transfer, 2016Co-Authors: Laurent Soucasse, Philippe Riviere, James B. Scoggins, Thierry E. Magin, Anouar SoufianiAbstract:In this study, a Hybrid Statistical Narrow Band (HSNB) Model is implemented to make fast and accurate predictions of radiative transfer effects on hypersonic entry flows. The HSNB Model combines a Statistical Narrow Band (SNB) Model for optically thick molecular systems, a box Model for optically thin molecular systems and continua, and a Line-By Line (LBL) description of atomic radiation. Radiative transfer calculations are coupled to a 1D stagnation-line flow Model under thermal and chemical nonequilibrium. Earth entry conditions corresponding to the FIRE 2 experiment, as well as Titan entry conditions corresponding to the Huygens probe, are considered in this work. Thermal nonequilibrium is described by a two temperature Model, although non-Boltzmann distributions of electronic levels provided by a Quasi-Steady State Model are also considered for radiative transfer. For all the studied configurations, radiative transfer effects on the flow, the plasma chemistry and the total heat flux at the wall are analyzed in detail. The HSNB Model is shown to reproduce LBL results with an accuracy better than 5% and a speed up of the computational time around two orders of magnitude. Concerning molecular radiation, the HSNB Model provides a significant improvement in accuracy compared to the Smeared-Rotational-Band Model, especially for Titan entries dominated by optically thick CN radiation. (C) 2016 Elsevier Ltd. All rights reserved.
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Coupled Flow, Radiation, and Ablation Simulations of Atmospheric Entry Vehicles using the Hybrid Statistical Narrow Band Model
45th AIAA Thermophysics Conference, 2015Co-Authors: James B. Scoggins, Philippe Riviere, Anouar Soufiani, Laurent Soucasse, Thierry MaginAbstract:A Model for coupled flow, radiation, and ablation calculations along the stagnation lines of atmospheric entry vehicles is developed to study the effects these coupled phenomena have on each other as well as the predicted quantities of interest to vehicle designers. The flow Model is based on the two-temperature, multicomponent, reacting Navier-Stokes equations coupled to radiative heat and photochemistry source terms and reduced to onedimension using the dimensionally reduced Navier-Stokes approximation. The radiative source terms are computed using the hybrid statistical narrow Band Model developed at the EM2C laboratory at Ecole Centrale Paris. This Model has previously been shown to accurately produce radiative properties at significantly reduced computational cost when compared to line-by-line calculations for uncoupled flows without ablation. In this work, the hybrid statistical narrow Band Model is coupled to the one-dimensional stagnation line flow solver with ablation. Ablation is treated through a simple steady-state ablation boundary condition with finite-rate heterogenous reactions capable of simulating ablation products blowing into the boundary layer. The Model is first used to simulate the effect of carbonaceous species in a typical boundary layer environment. In particular, it is shown that a boundary layer contaminated with a relatively small amount of ablation and pyrolysis products can have significantly lower transmissivities than a boundary layer with pure air. Finally, the peak heating point for the Apollo 4 command module is analyzed using each of the four possible coupling strategies: flow, flow and ablation, flow and radiation, and fully coupled. It is shown that for this case, radiation coupling is the dominant phenomena due to a relatively small carbon yield in the boundary layer. In addition, comparison of cumulative intensities with the radiometer measurement made during the flight shows excellent agreement and confirms the assumption that the radiometer cavity has little effect on the measured intensity due to the low amount of carbon present in the cavity.
Philippe Riviere - One of the best experts on this subject based on the ideXlab platform.
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Flow-radiation coupling for atmospheric entries using a Hybrid Statistical Narrow Band Model
Journal of Quantitative Spectroscopy and Radiative Transfer, 2016Co-Authors: Laurent Soucasse, Philippe Riviere, James B. Scoggins, Thierry E. Magin, Anouar SoufianiAbstract:In this study, a Hybrid Statistical Narrow Band (HSNB) Model is implemented to make fast and accurate predictions of radiative transfer effects on hypersonic entry flows. The HSNB Model combines a Statistical Narrow Band (SNB) Model for optically thick molecular systems, a box Model for optically thin molecular systems and continua, and a Line-By Line (LBL) description of atomic radiation. Radiative transfer calculations are coupled to a 1D stagnation-line flow Model under thermal and chemical nonequilibrium. Earth entry conditions corresponding to the FIRE 2 experiment, as well as Titan entry conditions corresponding to the Huygens probe, are considered in this work. Thermal nonequilibrium is described by a two temperature Model, although non-Boltzmann distributions of electronic levels provided by a Quasi-Steady State Model are also considered for radiative transfer. For all the studied configurations, radiative transfer effects on the flow, the plasma chemistry and the total heat flux at the wall are analyzed in detail. The HSNB Model is shown to reproduce LBL results with an accuracy better than 5% and a speed up of the computational time around two orders of magnitude. Concerning molecular radiation, the HSNB Model provides a significant improvement in accuracy compared to the Smeared-Rotational-Band Model, especially for Titan entries dominated by optically thick CN radiation. (C) 2016 Elsevier Ltd. All rights reserved.
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Coupled Flow, Radiation, and Ablation Simulations of Atmospheric Entry Vehicles using the Hybrid Statistical Narrow Band Model
45th AIAA Thermophysics Conference, 2015Co-Authors: James B. Scoggins, Philippe Riviere, Anouar Soufiani, Laurent Soucasse, Thierry MaginAbstract:A Model for coupled flow, radiation, and ablation calculations along the stagnation lines of atmospheric entry vehicles is developed to study the effects these coupled phenomena have on each other as well as the predicted quantities of interest to vehicle designers. The flow Model is based on the two-temperature, multicomponent, reacting Navier-Stokes equations coupled to radiative heat and photochemistry source terms and reduced to onedimension using the dimensionally reduced Navier-Stokes approximation. The radiative source terms are computed using the hybrid statistical narrow Band Model developed at the EM2C laboratory at Ecole Centrale Paris. This Model has previously been shown to accurately produce radiative properties at significantly reduced computational cost when compared to line-by-line calculations for uncoupled flows without ablation. In this work, the hybrid statistical narrow Band Model is coupled to the one-dimensional stagnation line flow solver with ablation. Ablation is treated through a simple steady-state ablation boundary condition with finite-rate heterogenous reactions capable of simulating ablation products blowing into the boundary layer. The Model is first used to simulate the effect of carbonaceous species in a typical boundary layer environment. In particular, it is shown that a boundary layer contaminated with a relatively small amount of ablation and pyrolysis products can have significantly lower transmissivities than a boundary layer with pure air. Finally, the peak heating point for the Apollo 4 command module is analyzed using each of the four possible coupling strategies: flow, flow and ablation, flow and radiation, and fully coupled. It is shown that for this case, radiation coupling is the dominant phenomena due to a relatively small carbon yield in the boundary layer. In addition, comparison of cumulative intensities with the radiometer measurement made during the flight shows excellent agreement and confirms the assumption that the radiometer cavity has little effect on the measured intensity due to the low amount of carbon present in the cavity.
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updated Band Model parameters for h2o co2 ch4 and co radiation at high temperature
International Journal of Heat and Mass Transfer, 2012Co-Authors: Philippe Riviere, Anouar SoufianiAbstract:Abstract Statistical narrow-Band (SNB) Model parameters for H2O, CO2, CH4 and CO, and correlated-k (CK) parameters for H2O and CO2 are generated from line by line calculations and recently improved spectroscopic databases in wide temperature and spectral ranges. Results from the new parameters are compared to direct line by line calculations and to results from earlier Model parameters [A. Soufiani, J. Taine, High temperature gas radiative property parameters of statistical narrow-Band Model for H2O, CO2 and CO and correlated-k (ck) Model for H2O and CO2, Int. J. Heat Mass Transfer 40 (1997) 987–991] in terms of Band averaged spectral transmissivities, Planck mean absorption coefficients, and total emissivities. The comparisons show first a good agreement between updated SNB, CK and LBL results. Significant improvements on earlier parameters are observed for H2O and CO2, especially at very high temperatures and path lengths. Model parameters and computer programs illustrating their implementation are provided as Supplementary data .
