Source-linked AI summary
Mutation++: MUlticomponent Thermodynamic And Transport properties for IONized gases in C++
James B. Scoggins, Vincent Leroy, Georgios Bellas-Chatzigeorgis, Bruno Dias, Thierry E. Magin
TL;DR
Physicochemical-property computation for partially ionized gases spans many nonequilibrium conditions and requires numerous models, algorithms, and data. Mutation++ addresses this need with an object-oriented C++ library that separates property calculations from simulation tools and supports thermodynamic, transport, kinetic, equilibrium, and gas-surface computations. The resulting framework is open source, extensible, and has been used across hypersonic-flow, plasma, pyrolysis, meteor, and material-response applications.
Problem
Computing properties for partially ionized gases across thermochemical nonequilibrium requires many specialized models, algorithms, and data whose implementation and maintenance are costly.
Method
Mutation++ uses an object-oriented C++ framework with a clean API and weak coupling between local-state property calculations and client simulation tools.
Results
Mutation++ v1.0.0 computes thermodynamic, transport, kinetic, equilibrium, chemical-production, energy-transfer, and gas-surface properties for non- to fully ionized gas mixtures.
Takeaways & Limitations
The open-source framework supports extensible reuse of models, algorithms, and data across research and selected commercial applications.
Takeaways & Limitations
The kinetics formulation assumes each forward reaction rate is a function of a single reaction variable.
Abstract
from arXiv · showhide
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.
1. Motivation and Significance
Mutation++ addresses the substantial effort required to implement and maintain physicochemical models for thermochemical nonequilibrium simulations by centralizing models, algorithms, and data in a reusable library. Version 1.0.0 provides an open-source, modular framework for computing properties used across diverse applications.
- Thermochemical nonequilibrium properties are essential for applications including hypersonic flows, solar physics, ion thrusters, medical plasmas, combustion, meteor phenomena, and biomass pyrolysis.
- Model selection affects mixture thermodynamic and transport properties, chemical production rates, and energy transfer rates needed to close fluid conservation laws.These properties depend on specialized algorithms and data, including partition functions, collision integrals, and reaction-rate coefficients.
- Implementing, testing, and maintaining thermal-nonequilibrium models, algorithms, and data requires substantial human effort and development time.Updating hardcoded codes becomes especially costly as new models, algorithms, or data become available.
- Mutation++ centralizes model and algorithm development in a single library to reduce implementation work and promote code reuse, testing, and open collaboration across CFD codes.
- The library targets accurate properties, efficient C++ algorithms, extensibility, consistent simulation-tool interfaces, readable databases, and cross-community sharing.
- Version 1.0.0 is open source under the LGPL v3 and presents thermodynamics, transport, chemical kinetics, and gas-surface interaction modules.
2. Software Description
Mutation++ organizes thermodynamic, transport, equilibrium, chemical-kinetics, and gas-surface models into an extensible C++ library for coupling physicochemical properties to CFD. Its modules support swappable databases and algorithms, automated reaction classification, and dynamically constructed surface models.
- Generalized Conservation Equations: Mutation++ uses a generalized conservation-law framework whose constitutive relations provide thermodynamic, transport, chemical, and energy-transfer properties from the local state.The specific state, flux, and source forms depend on the coordinate system, physical model, and thermochemical model.
- Architecture: The object-oriented architecture exposes a documented Mixture interface with separated modules, continuous integration, regression tests, and black-box tests.The architecture is illustrated through a simplified UML class diagram and module-specific components.
- Thermodynamics: Thermodynamic databases are abstracted from mixture-property calculations, allowing database replacement with minimal effort and supporting equilibrium and thermal-nonequilibrium models.Implemented formats include NASA 7- and 9-coefficient databases and an XML RRHO model, alongside a database containing more than 1200 neutral and ionized species.
- Thermodynamics: The MPGFC solver computes multiphase, constrained equilibrium compositions and is reported as robust for all well-posed constraints.It is based on a single-phase Gibbs function continuation method.
- Transport: Transport algorithms are plug-and-play through self-registering classes, while collision data are handled by a CollisionDB object with extensible data and model support.The transport interfaces cover thermal conductivity, thermal diffusion ratios, multicomponent diffusion, and shear viscosity.
- Kinetics: The kinetics module computes finite-rate species production rates, automatically classifies reaction types with a decision tree, and evaluates reaction terms through specialized managers.The Kinetics class also evaluates the Jacobian with respect to species densities and temperatures.
- Gas-Surface Interactions: Gas-surface models provide client codes with fluxes and source terms from dynamically assembled surface balance equations using built-in terms and custom XML models.The framework supports chemically active, impermeable, and porous surfaces with fixed outgassing.
3. Illustrative examples
Mutation++ is illustrated through thermodynamic and transport calculations for equilibrium air and through a B-prime ablation-table calculation. The ablation example couples Gibbs-energy minimization with elemental conservation and compares results from custom and NASA CEA thermodynamic databases.
- Fig. 5 computes thermodynamic and transport properties for an 11-species, isobaric air mixture in thermochemical equilibrium.The comparison uses NASA-9 and RRHO thermodynamic databases.
- The air-property example compares equilibrium mole fractions and thermodynamic properties across NASA-9 and RRHO databases, with available comparisons to published curve fits and conductivity data.Frozen and equilibrium curves are shown for specific heat at constant pressure and specific heat ratio.
- Equilibrium ablation rates: B-prime tables describe equilibrium surface-gas composition and mass loss from ablating thermal-protection materials undergoing reactions such as oxidation or nitridation.The calculation assumes a thin control volume and equal species diffusion coefficients.
- Equilibrium ablation rates: The elemental-conservation relation uses wall, char, pyrolysis-gas, and boundary-layer-edge elemental mass fractions to determine the mass-blowing rate.The passages define B′ as a mass-blowing rate nondimensionalized by the boundary-layer-edge mass flux and identify CM as the local Stanton number for mass transfer.
- Equilibrium ablation rates: Coupling the conservation relation with Gibbs-energy minimization at a known surface condition yields species composition and char mass-blowing rate B′.Mutation++ results are compared with results obtained using the NASA Chemical Equilibrium with Applications thermodynamic database.
4. Impact
Mutation++ lowers the cost of developing and testing physicochemical models by providing an efficient, extensible framework that couples with CFD tools and supports collaboration. Its use has expanded beyond hypersonic flows into diverse research and commercial applications.
- Mutation++ promotes collaboration across hypersonics, combustion, and plasma physics by lowering the cost of developing physicochemical models, data, and algorithms.
- Its extensible framework couples with existing CFD tools, enabling researchers to test thermodynamic, transport, chemical, and numerical models effectively.
- Continuous integration supports collaborative testing, bug fixing, and maintenance so users can benefit from one another’s work.
- Mutation++ has expanded from hypersonic atmospheric-entry flows to biomass pyrolysis, solar physics, magnetized transport, meteor phenomena, and limited commercial applications.
5. Conclusions
Mutation++ provides an object-oriented framework and consistent API for computing properties of gas mixtures across the thermochemical nonequilibrium spectrum. Version 1.0.0 is openly available under LGPL v3.0, with future versions planned to add features and flexibility.
- Mutation++ computes thermodynamic, transport, and kinetic properties for nonionized to fully ionized gas mixtures across the thermochemical nonequilibrium spectrum.
- Its object-oriented framework weakly couples property computation to simulation tools through a clean and consistent API.
- Version v1.0.0 is freely available on GitHub under an LGPL v3.0 license and uses continuous integration with periodic versioning.
- Future versions aim to provide additional features and greater flexibility for end users.