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Title: Deterministic numerical simulation of the Boltzmann and kinetic model equations for classical and quantum dilute gases
Author: Wu, Lei
Awarding Body: University of Strathclyde
Current Institution: University of Strathclyde
Date of Award: 2013
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In the areas of low-density aerodynamics, vacuum industry, and micro-electromechanical systems, the Navier-Stokes-Fourier equations fail to describe the gas dynamics when the molecular mean free path is not negligible compared to the characteristic flow length. Instead, the Boltzmann equation is used to account for the non-continuum nature of the rarefied gas. Although many efforts have been made to derive the macroscopic equations from the Boltzmann equation, the numerical simulation of the Boltzmann equation is indispensable in the study of moderately and highly rarefied gas. We aim to develop an accurate and efficient deterministic numerical method to solve the Boltzmann equation. The fast spectral method [1], originally developed by Mouhot and Pareschi for the numerical approximation of the collision operator, is extended to deal with other collision kernels, such as those corresponding to the soft, Lennard-Jones, and rigid attracting potentials. The accuracy of the fast spec tral method is checked by comparing our numerical results with the exact Bobylev-Krook-Wu solutions of the space-homogeneous Boltzmann equation for a gas of Maxwell molecules. It is found that the accuracy is improved by replacing the trapezoidal rule with Gauss-Legendre quadrature in the calculation of the kernel mode, and the conservation of momentum and energy are ensured by the Lagrangian multiplier method without loss of spectral accuracy. The relax-to-equilibrium processes of different collision kernels with the same value of shear viscosity are then compared and the use of special collision kernels is justified. An iteration scheme, where the numerical errors decay exponentially, is employed to obtain stationary solutions of the space-inhomogeneous Boltzmann equation. Sever classical benchmarking problems (the normal shock wave, and the planar Fourier/Couette/force-driven Poiseuille flows) are investigated. For normal shock waves, our numerical results are compared with the finite-difference solution of the Boltzmann equation for hard sphere molecules, the experimental data, and the molecular dynamics simulation of argon using the realistic Lennard-Jones potential. For the planar Fourier/Couette/force-driven Poiseuille flows, our results are compared with the Direct Simulation Monte Carlo method. Excellent agreements are observed in all test cases. The fast spectral method is then applied to the linearised Boltzmann equation. With appropriate velocity discretization, the classical Poiseuille and thermal creep flows are solved up to Kn 106, where the accuracy in the mass and heat flow rates is comparable to those from the finite-difference method and the efficiency is much better than the low-noise Direct Simulation Monte Carlo method. The fast spectral method is also extended to solve the Boltzmann equation for binary gas mixtures, both in the framework of classical and quantum mechanics. With the accurate numerical solution provided by the fast spectral method, we check the accuracy of kinetic model equations to find out at what flow regime can the complicated Boltzmann collision kernel be replaced by the simple kinetic ones. We also solve the collective oscillation of quantum gas confined in external trap and compare the numerical solutions with the experimental data, indicating the applicability of quantum kinetic model.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available