Projects per year

### Abstract

A kinetic model of the Boltzmann equation for non-vibrating polyatomic gases is proposed, based on the Rykov model for diatomic gases. We adopt two velocity distribution functions (VDFs) to describe the system state; inelastic collisions are the same as in the Rykov model, but elastic collisions are modelled by the Boltzmann collision operator (BCO) for monatomic gases, so that the overall kinetic model equation reduces to the Boltzmann equation for monatomic gases in the limit of no translational–rotational energy exchange. The free parameters in the model are determined by comparing the transport coefficients, obtained by a Chapman–Enskog expansion, to values from experiment and kinetic theory. The kinetic model equations are solved numerically using the fast spectral method for elastic collision operators and the discrete velocity method for inelastic ones. The numerical results for normal shock waves and planar Fourier/Couette flows are in good agreement with both conventional direct simulation Monte Carlo (DSMC) results and experimental data. Poiseuille and thermal creep flows of polyatomic gases between two parallel plates are also investigated. Finally, we find that the spectra of both spontaneous and coherent Rayleigh–Brillouin scattering (RBS) compare well with DSMC results, and the computational speed of our model is approximately 300 times faster. Compared to the Rykov model, our model greatly improves prediction accuracy, and reveals the significant influence of molecular models. For coherent RBS, we find that the Rykov model could overpredict the bulk viscosity by a factor of two.

Original language | English |
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Pages (from-to) | 24-50 |

Number of pages | 27 |

Journal | Journal of Fluid Mechanics |

Volume | 763 |

Early online date | 9 Dec 2014 |

DOIs | |

Publication status | Published - 25 Jan 2015 |

### Keywords

- computational methods
- kinetic theory
- rarefied gas flow

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## Projects

- 2 Finished

## UK Consortium on Mesoscale Engineering Sciences (UKCOMES)

Zhang, Y.

EPSRC (Engineering and Physical Sciences Research Council)

1/06/13 → 31/05/18

Project: Research

## Multiscale Simulation of Micro and Nano Gas Flows

Zhang, Y. & Reese, J.

EPSRC (Engineering and Physical Sciences Research Council)

1/08/11 → 31/01/15

Project: Research

## Equipment

## Cite this

Wu, L., White, C., Scanlon, T. J., Reese, J. M., & Zhang, Y. (2015). A kinetic model of the Boltzmann equation for non-vibrating polyatomic gases.

*Journal of Fluid Mechanics*,*763*, 24-50. https://doi.org/10.1017/jfm.2014.632