# A mathematical and numerical framework for the analysis of compressible thermal convection in gases at very high temperatures

## Abstract

The relevance of non-equilibrium phenomena, nonlinear behavior, gravitational effects and fluid compressibility in a wide range of problems related to high-temperature gas-dynamics, especially in thermal, mechanical and nuclear engineering, calls for a concerted approach using the tools of the kinetic theory of gases, statistical physics, quantum mechanics, thermodynamics and mathematical modeling in synergy with advanced numerical strategies for the solution of the Navier–Stokes equations. The reason behind such a need is that in many instances of relevance in this field one witnesses a departure from canonical models and the resulting inadequacy of standard CFD approaches, especially those traditionally used to deal with thermal (buoyancy) convection problems. Starting from microscopic considerations and typical concepts of molecular dynamics, passing through the Boltzmann equation and its known solutions, we show how it is possible to remove past assumptions and elaborate an algorithm capable of targeting the broadest range of applications. Moving beyond the Boussinesq approximation, the Sutherland law and the principle of energy equipartition, the resulting method allows most of the fluid properties (density, viscosity, thermal conductivity, heat capacity and diffusivity, etc.) to be derived in a rational and natural way while keeping empirical contamination to the minimum. Special attention is deserved asmore »

- Authors:

- Publication Date:

- OSTI Identifier:
- 22572303

- Resource Type:
- Journal Article

- Journal Name:
- Journal of Computational Physics

- Additional Journal Information:
- Journal Volume: 313; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0021-9991

- Country of Publication:
- United States

- Language:
- English

- Subject:
- 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ALGORITHMS; BENCHMARKS; BOLTZMANN EQUATION; CONTAMINATION; CONVECTION; DEGREES OF FREEDOM; EXCITATION; GASES; MATHEMATICAL MODELS; MATHEMATICAL SOLUTIONS; MOLECULAR DYNAMICS METHOD; NAVIER-STOKES EQUATIONS; NONLINEAR PROBLEMS; NUCLEAR ENGINEERING; QUANTUM MECHANICS; SPECIFIC HEAT; THERMAL CONDUCTIVITY

### Citation Formats

```
Lappa, Marcello.
```*A mathematical and numerical framework for the analysis of compressible thermal convection in gases at very high temperatures*. United States: N. p., 2016.
Web. doi:10.1016/J.JCP.2016.02.062.

```
Lappa, Marcello.
```*A mathematical and numerical framework for the analysis of compressible thermal convection in gases at very high temperatures*. United States. doi:10.1016/J.JCP.2016.02.062.

```
Lappa, Marcello. Sun .
"A mathematical and numerical framework for the analysis of compressible thermal convection in gases at very high temperatures". United States. doi:10.1016/J.JCP.2016.02.062.
```

```
@article{osti_22572303,
```

title = {A mathematical and numerical framework for the analysis of compressible thermal convection in gases at very high temperatures},

author = {Lappa, Marcello},

abstractNote = {The relevance of non-equilibrium phenomena, nonlinear behavior, gravitational effects and fluid compressibility in a wide range of problems related to high-temperature gas-dynamics, especially in thermal, mechanical and nuclear engineering, calls for a concerted approach using the tools of the kinetic theory of gases, statistical physics, quantum mechanics, thermodynamics and mathematical modeling in synergy with advanced numerical strategies for the solution of the Navier–Stokes equations. The reason behind such a need is that in many instances of relevance in this field one witnesses a departure from canonical models and the resulting inadequacy of standard CFD approaches, especially those traditionally used to deal with thermal (buoyancy) convection problems. Starting from microscopic considerations and typical concepts of molecular dynamics, passing through the Boltzmann equation and its known solutions, we show how it is possible to remove past assumptions and elaborate an algorithm capable of targeting the broadest range of applications. Moving beyond the Boussinesq approximation, the Sutherland law and the principle of energy equipartition, the resulting method allows most of the fluid properties (density, viscosity, thermal conductivity, heat capacity and diffusivity, etc.) to be derived in a rational and natural way while keeping empirical contamination to the minimum. Special attention is deserved as well to the well-known pressure issue. With the application of the socalled multiple pressure variables concept and a projection-like numerical approach, difficulties with such a term in the momentum equation are circumvented by allowing the hydrodynamic pressure to decouple from its thermodynamic counterpart. The final result is a flexible and modular framework that on the one hand is able to account for all the molecule (translational, rotational and vibrational) degrees of freedom and their effective excitation, and on the other hand can guarantee adequate interplay between molecular and macroscopic-level entities and processes. Performances are demonstrated by computing some incompressible and compressible benchmark test cases for thermal (gravitational) convection, which are then extended to the high-temperature regime taking advantage of the newly developed features.},

doi = {10.1016/J.JCP.2016.02.062},

journal = {Journal of Computational Physics},

issn = {0021-9991},

number = ,

volume = 313,

place = {United States},

year = {2016},

month = {5}

}