Publications

Journal Articles

1. Shock interactions in inviscid air and CO2–N2 flows in thermochemical non-equilibrium Shock Waves , 2021. C. Garbacz, W. T. Maier, J. B. Scoggins, T. D. Economon, T. Magin, J. J. Alonso, M. Fossati [Abs]

   The present study aims at providing insights into shock wave interference patterns in gas flows when a mixture different than air is considered. High-energy non-equilibrium flows of air and CO2–N2 over a double-wedge geometry are studied numerically. The impact of freestream temperature on the non-equilibrium shock interaction patterns is investigated by simulating two different sets of freestream conditions. To this purpose, the SU2 solver has been extended to account for the conservation of chemical species as well as multiple energies and coupled to the Mutation++ library (Multicomponent Thermodynamic And Transport properties for IONized gases in C++) that provides all the necessary thermochemical properties of the mixture and chemical species. An analysis of the shock interference patterns is presented with respect to the existing taxonomy of interactions. A comparison between calorically perfect ideal gas and non-equilibrium simulations confirms that non-equilibrium effects greatly influence the shock interaction patterns. When thermochemical relaxation is considered, a type VI interaction is obtained for the CO2-dominated flow, for both freestream temperatures of 300 K and 1000 K; for air, a type V six-shock interaction and a type VI interaction are obtained, respectively. We conclude that the increase in freestream temperature has a large impact on the shock interaction pattern of the air flow, whereas for the CO2–N2 flow the pattern does not change.

2. Mutation++: MUlticomponent Thermodynamic And Transport properties for IONized gases in C++ SoftwareX 12, 2020. James B. Scoggins, Vincent Leroy, Georgios Bellas-Chatzigeorgis, Bruno Dias, Thierry E. Magin [Abs] [arXiv] [PDF]

   The Mutation++ library provides accurate and efficient computation of physicochemical properties associated with partially ionized gases in various degrees of thermal nonequilibrium. With v1.0.0, users can compute thermodynamic and transport properties, multiphase linearly-constrained equilibria, chemical production rates, energy transfer rates, and gas-surface interactions. The framework is based on an object-oriented design in C++, allowing users to plug-and-play various models, algorithms, and data as necessary. Mutation++ is available open-source under the GNU Lesser General Public License v3.0.

3. Luminosity calculation of meteor entry based on detailed flow simulations in the continuum regime Astronomy and Astrophysics 635:A184, 2020. B. Dias, J.B. Scoggins, T.E. Magin [Abs] [PDF]

   *Context.* Composition, mass, and trajectory parameters of meteors can be derived by combining observations with the meteor physics equations. The fidelity of these equations, which rely on heuristic coefficients, significantly affects the accuracy of the properties inferred. *Aims.* Our objective is to present a methodology that can be used to compute the luminosity of meteor entry based on detailed flow simulations in the continuum regime. *Methods.* The methodology consists in solving the Navier-Stokes equations using state-of-the-art physico-chemical models for hy- personic flows. It includes accurate boundary conditions to simulate the surface evaporation of the molten material and coupled flow-radiation effects. Such detailed simulations allow for the calculation of heat-transfer coefficients and luminous efficiency, which can be incorporated into the meteor physics equations. Finally, we integrate the radiative transfer equation over a line of sight from the ground to the meteor to derive the luminosity magnitude. *Results.* We use the developed methodology to simulate the Lost City bolide and to derive the luminosity magnitude, obtaining good agreement between numerical results and observations. The computed color index is more prominent than the observations. This is attributed to a lack of refractory elements such as Ca in the modeled flow that might originate from the vaporization of droplets in the trail, a phenomenon currently not included in the model.

4. Consistent transport properties in multicomponent two-temperature magnetized plasmas Astronomy and Astrophysics 635:A87, 2020. Q. Wargnier, A. Alvarez Laguna, J.B. Scoggins, N.N. Mansour, M. Massot, T.E. Magin [Abs] [PDF]

   *Aims.* We present a fluid model that has been developed for multicomponent two-temperature magnetized plasmas in chemical non- equilibrium for the partially to fully ionized collisional regimes. We focus on transport phenomena with the aim of representing the atmosphere of the Sun. *Methods.* This study is based on an asymptotic fluid model for multicomponent plasmas derived from kinetic theory, yielding a rigorous description of the dissipative effects. The governing equations and consistent transport properties are obtained using a multi- scale Chapman-Enskog perturbative solution to the Boltzmann equation based on a dimensional analysis. The mass disparity between free electrons and heavy particles is accounted for, as well as the influence of the electromagnetic field. We couple this model to the Maxwell equations for the electromagnetic field and derive the generalized Ohm’s law for multicomponent plasmas. The model inher- its a well-identified mathematical structure leading to an extended range of validity for the Sun’s atmospheric conditions. We compute consistent transport properties by means of a spectral Galerkin method using the Laguerre-Sonine polynomial approximation. Two non-vanishing polynomial terms are used when deriving the transport systems for electrons, whereas only one term is retained for heavy particles. *Results.* In a simplified framework where the plasma is fully ionized, we compare the transport properties for the lower solar atmo- sphere to conventional expressions for magnetized plasmas attributed to Braginskii, showing a good agreement between both results. For more general partially ionized conditions, representative of the lower solar atmosphere, we compute the muticomponent transport properties corresponding to the species diffusion velocities, heavy-particle and electron heat fluxes, and viscous stress tensor of the model for a helium-hydrogen mixture in local thermodynamic equilibrium. The model is assessed for the 3D radiative magnetohy- drodynamic simulation of a pore at the Sun photosphere. The resistive term is found to dominate mainly the dynamics of the electric field at the pore location. The battery term for heavy particles appears to be higher at the pore location and at some intergranulation boundaries.

5. Transport properties of carbon-phenolic gas mixtures Physics of Fluids 31:096102, 2019. A. Bellemans, J.B. Scoggins, R.L. Jaffe, T.E. Magin [Abs] [PDF]

   The development of a new generation of ablative thermal protection systems based on carbon-phenolic composite materials demands the accurate determination of transport properties of pyrolysis gases mixed in various atmospheres. The present work provides recommended collision data for the calculation of the transport properties for Mars and Earth re-entries. A review of available potential data is given for species in the atmospheres of Earth and Mars. Additional data are provided for species formed during the degradation of the theoretical ablative composite for open testing material. Dipole polarizabilities are calculated from ab initio methods and used for the calculation of transport properties of reduced pyrolysis mixtures over a temperature range representative of the boundary layer for atmospheric entry flows.

6. A kinetic BGK edge-based scheme including vibrational and electronic energy modes for High-Mach flows Computers and Fluids 185:1-12, 2019. M. Fossati, A. Mogavero, J. Herrera-Montojo, J.B. Scoggins, T. Magin [Abs] [PDF]

   A first principles formulation for the calorically imperfect behaviour of gases is here proposed within a Boltzmann-type discretisation of the Navier-Stokes equations. The formulation is intended to enhance the consistency of gas kinetic schemes (GKS) with the physics of supersonic and hypersonic regimes where vibrational and electronic energy modes are activated before any thermal nonequilibrium or chemical activity takes place. The so-called node-pair BGK scheme, an edge-based implementation of the GKS, is considered in the present work for the implementation of a thermodynamic model where the calorically imperfect behavior is obtained from a modification of the way the different moments of the particle distribution function are computed and eventually used to determine the fluxes of conserved quantities across the boundary of each control volume. The method is validated on a series of canonical test cases for supersonic and hypersonic flows.

7. A generic local thermal equilibrium model for porous reactive materials submitted to high temperatures International Journal of Heat and Mass Transfer 108:1406-1417, 2017. J. Lachaud, J.B. Scoggins, T.E. Magin, M.G. Meyer, N.N. Mansour [Abs] [PDF]

   Many engineering applications involve reacting porous materials submitted to high temperatures. This work presents a detailed but pragmatic heat and mass transfer model for porous materials containing several solid phases and a single gas phase. The detailed chemical interactions occurring between the solid phases and the gas phase are modeled at the pore scale assuming local thermal equilibrium. Homogenized models are obtained for solid pyrolysis, pyrolysis species injection in the gas phase, heterogeneous reactions between the solid phases and the gas phase, and homogeneous reactions in the gas phase. The chemistry models are integrated in a macroscopic model making use of volume-averaged governing equations for the conservation of solid mass, gas mass, species (finite-rate chemistry) or elements (equilibrium chemistry), momentum, and energy. The model has been implemented in the Porous Material Analysis Toolbox based on OpenFoam (PATO), distributed Open Source by NASA. Applications to two high-temperature engineering problems are presented. The first application concerns the design of heat-shields of space vehicles. The second one aims at improving the understanding of biomass pyrolysis for the production of biohydrocarbons.

8. Thermodynamic properties of carbon–phenolic gas mixtures Aerospace Science and Technology 166:177-192, 2017. James B. Scoggins, Jason Rabinovitch, Benjamin Barros-Fernandez, Alexandre Martin, Jean Lachaud, Richard L. Jaffe, Nagi N. Mansour, Guillaume Blanquart, Thierry E. Magin [Abs] [PDF]

   Accurate thermodynamic properties for species found in carbon-phenolic gas mixtures are essential in predicting material response and heating of carbon-phenolic heat shields of planetary entry vehicles. A review of available thermodynamic data for species found in mixtures of carbon-phenolic pyrolysis and ablation gases and atmospheres rich with C, H, O, and N such as those of Earth, Mars, Titan, and Venus, is performed. Over 1200 unique chemical species are identified from four widely used thermodynamic databases and a systematic procedure is described for combining these data into a comprehensive model. The detailed dataset is then compared with the Chemical Equilibrium with Applications thermodynamic database developed by NASA in order to quantify the differences in equilibrium thermodynamic properties obtained with the two databases. In addition, a consistent reduction methodology using the mixture thermodynamic properties as an objective function is developed to generate reduced species sets for a variety of temperature, pressure, and elemental composition spaces. It is found that 32 and 23 species are required to model carbon-phenolic pyrolysis gases mixed with air and CO2, respectively, to maintain a maximum error in thermodynamic quantities below 10%.

9. Flow-radiation coupling for atmospheric entries using a Hybrid Statistical Narrow Band model Journal of Quantitative Spectroscopy and Radiative Transfer 180:55-69, 2016. Laurent Soucasse, James B. Scoggins, Philippe Rivière, Thierry E. Magin, Anouar Soufiani [Abs] [PDF]

   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.

10. Experimental investigation of ablation and pyrolysis processes of carbon-phenolic ablators in atmospheric entry plasmas International Journal of Heat and Mass Transfer 100:810-824, 2016. Bernd Helber, Alessandro Turchi, James B. Scoggins, Annick Hubin, Thierry E. Magin [Abs] [PDF]

    We study the ablation and transient pyrolysis outgassing of the carbon-phenolic ablators AQ61 and Asterm in air and nitrogen plasmas. We investigate their resistance to high heating conditions, and characterize gas-surface interaction phenomena, including the interaction of the pyrolysis gases with the hot plasma flow. The experiments were carried out in the Plasmatron facility of the von Karman Institute for Fluid Dynamics. The aero-thermodynamic environment of atmospheric entry in the boundary layer of a test object was selected with surface temperatures between 1900 K and 2800 K, and test chamber pressures of 15 hPa, 100 hPa, and 200 hPa. Those conditions led to recession rates between 39 lm/s and 83 lm/s in air plasmas. Micrographs revealed oxidation of the char layer and carbon fibers. Carbon deposition in the form of soot was observed on samples tested in nitrogen, contrary to air ablation where charred resin was not found at the surface. We propose an approach to estimate the temporally resolved pyrolysis outgassing rate, based on the emission signature of pyrolysis products and the volume change of the sample. The temporal recession rate was obtained from high-speed camera imaging. This enabled evaluation of the surface recession as a function of the pyrolysis outgassing rate, which was then compared to numerical estimates predicted by thermochemical equilibrium tables. The thermochemical equilibrium model generally underpredicted experimental recession rates, particularly at low pressure (15 hPa). Stronger mechanical failure of the material was ruled out as experiments at the same test conditions in nitrogen plasmas did not show any significant recession. Micrographs did not indicate internal oxidation of the material, neither was spallation observed during the low pressure experiments.

11. Gibbs function continuation for linearly constrained multiphase equilibria Combustion and Flame 162(12):4514-4522, 2015. James B. Scoggins, Thierry E. Magin [Abs] [PDF]

    The stable computation of linearly constrained, multiphase, chemical equilibrium compositions is an important topic for a wide range of industrial and academic applications. Numerous computational methods have been developed to solve such problems which are, in general, susceptible to failure under certain conditions due to numerical stiffness. In this work, we present a Gibbs function continuation method for linearly constrained multiphase equilibrium calculations. The method converts the nonlinear Element Potential Equations - derived from the minimization of the mixture Gibbs free energy using the Lagrange multiplier technique - into an initial value problem which can be stably integrated through the use of a property of linear least squares solutions. The stability and convergence properties of the proposed method are derived and it is shown that the single phase method arises as a special case of the multiphase algorithm when only one phase is considered. Two test cases are presented to clarify and demonstrate the accuracy and robustness of the method.

12. Detailed chemical equilibrium model for porous ablative materials International Journal of Heat and Mass Transfer 90:1034-1045, 2015. Jean Lachaud, Tom van Eekelen, James B. Scoggins, Thierry E. Magin, Nagi N. Mansour [Abs] [PDF]

    Ablative materials are used in thermal protection systems for atmospheric re-entry vehicle heat shields. A detailed chemical equilibrium heat and mass transport model for porous ablators is presented for the first time. The governing equations are volume-averaged forms of the conservation equations for gas density, gas elements, solid mass, gas momentum, and total energy. The element (gas) fluxes are coupled at the surface of the material with an inlet/outlet boundary condition, allowing modeling either atmospheric gases entering the porous material by forced convection or pyrolysis gases exiting the material. The model is implemented in the Porous material Analysis Toolbox based on OpenFOAM (PATO). The thermo- dynamics and chemistry library Mutation++ is used as a third party library to compute equilibrium compositions, gas properties, and solve the state-of-the-art boundary layer approximation to provide the ablation rate and the element mass fractions at the surface of the material. The model is applied to the detailed analysis of boundary layer and pyrolysis gas flows within a porous carbon/phenolic ablator characterized in a state-of-the-art arc-jet test. The selected configuration consists of an iso-flux ellipsoid-cylinder sample submitted to a 2.5 MW/m2 heat flux with a decreasing pressure gradient from the stagnation point to the cylinder’s side. During the first tenths of a second of the test, boundary layer gases percolate through the sample. Then, as the sample heats up, the internal pressure increases inside the sample due to pyrolysis–gas production. The resulting pressure gradient blocks the boundary layer gases and leads to a pyrolysis gas flow that separates into two streams: one going towards the upper surface, and one going towards the lower pressure side under the shoulder of the sample. We show that the temperature profile is modified when using the detailed mass transport model. The sample’s sub-shoulder zone is significantly cooled down while a temperature increase is observed in-depth. Implementing the model of this study in space agency codes will allow improving ground-test analyses and help provide more accurate material properties for design.