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We propose two models of the Boltzmann equation (BGK and Fokker-Planck models) for rarefied flows of thermally perfect gases. These models take into account various models of energy, which are required for high temperature flows, like for…

Mathematical Physics · Physics 2020-01-27 J. Mathiaud , Luc Mieussens

We present a numerical method for simulating rarefied gases that interact with moving boundaries and rigid bodies. The gas is described by the BGK equation in Lagrangian form and solved using an Arbitrary Lagrangian-Eulerian method, in…

Numerical Analysis · Mathematics 2026-04-28 Klaas Willems , Axel Klar , Giovanni Russo , Giovanni Samaey , Sudarshan Tiwari

We study a quasi-incompressible Navier--Stokes/Cahn--Hilliard coupled system which describes the motion of two macroscopically immiscible incompressible viscous fluids with partial mixing in a small interfacial region and long-range…

Analysis of PDEs · Mathematics 2025-08-12 Mingwen Fei , Xiang Fei , Daozhi Han , Yadong Liu

In this paper, we study the hydrodynamic limit transition from the Boltzmann equation for gas mixtures to the two-fluid macroscopic system. Employing a meticulous dimensionless analysis, we derive several novel hydrodynamic models via the…

Analysis of PDEs · Mathematics 2024-08-08 Zhendong Fang , Kunlun Qi

This paper is concerned with a diffuse interface model for the gas-liquid phase transition. The model consists the compressible Navier-Stokes equations with van der Waals equation of state and a modified Allen-Cahn equation. The global…

Analysis of PDEs · Mathematics 2018-10-02 Qiaolin He , Ming Mei , Xiaoding Shi , Xiaoping Wang

We study a thermodynamically consistent diffuse-interface model that describes the motion of two macroscopically immiscible, incompressible, and viscous Newtonian fluids with unmatched densities. This model is compatible with continuum…

Analysis of PDEs · Mathematics 2026-04-30 Mingwen Fei , Xiang Fei , Yadong Liu , Hao Wu

In this paper, we prove that a local weak solution to the $d$-dimensional incompressible Navier-Stokes equations ($d \geq 2$) can be constructed by taking the hydrodynamic limit of a velocity-discretized Boltzmann equation with a simplified…

Analysis of PDEs · Mathematics 2026-04-15 Zhongyang Gu , Xin Hu , Pritpal Matharu , Bartosz Protas , Makiko Sasada , Tsuyoshi Yoneda

When the flow is sufficiently rarefied, a temperature gradient, for example, between two walls separated by a few mean free paths, induces a gas flow---an observation attributed to the thermo-stress convection effects at microscale. The…

In this paper we have applied a Semi-Lagrangian schemes with meshfree interpolation, based on a Moving Least Squares (MLS) method, to solve the BGK model for rarefied gas dynamics. Sod's shock tube problems are presented for a large range…

Numerical Analysis · Mathematics 2019-09-20 Sudarshan Tiwari , Axel Klar , Giovanni Russo

We derive a novel thermodynamically consistent Navier--Stokes--Cahn--Hilliard system with dynamic boundary conditions. This model describes the motion of viscous incompressible binary fluids with different densities. In contrast to previous…

Analysis of PDEs · Mathematics 2023-10-25 Andrea Giorgini , Patrik Knopf

We propose a BGK-type kinetic model for a binary gas mixture, designed to serve as a kinetic formulation of compressible two-phase fluid dynamics. The model features species-dependent adiabatic exponents, and the relaxation operator is…

Analysis of PDEs · Mathematics 2025-06-25 Seung Yeon Cho , Young-Pil Choi , Byung-Hoon Hwang , Sihyun Song

In rarefied gas flows, the spatial grid size could vary by several orders of magnitude in a single flow configuration (e.g., inside the Knudsen layer it is at the order of mean free path of gas molecules, while in the bulk region it is at a…

Fluid Dynamics · Physics 2021-04-02 Lei Wu

In this paper, we present a simple and accurate lattice Boltzmann (LB) model for immiscible two-phase flows, which is able to deal with large density contrasts. This model utilizes two LB equations, one of which is used to solve the…

Computational Physics · Physics 2018-09-12 Hong Liang , Jiangrong Xu , Jiangxing Chen , Huili Wang , Zhenhua Chai , Baochang Shi

We propose a thermodynamically consistent phase-field model for the flow of a mixture of two different viscous incompressible fluids of equal density in a bounded domain. We prove the well-posedness of local-in-time strong solutions by…

Analysis of PDEs · Mathematics 2025-11-18 Helmut Abels , Alice Marveggio , Andrea Poiatti

The simulation of rarefied gas flow based on the Boltzmann equation is challenging, especially when the gas mixtures have disparate molecular masses. In this paper, a computationally tractable kinetic model is proposed for monatomic gas…

Fluid Dynamics · Physics 2024-03-12 Qi Li , Jianan Zeng , Lei Wu

We study efficient simulation of steady state for rarefied gas flow, which is modeled by the Boltzmann equation with BGK-type collision term. A nonlinear multigrid solver is proposed to resolve the efficiency issue by the following…

Numerical Analysis · Mathematics 2022-06-28 Zhicheng Hu , Guanghan Li

In this paper we present a numerical scheme to simulate a moving rigid body with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated by solving the Boltzmann equation using a DSMC particle method. The motion of the…

Computational Physics · Physics 2015-06-22 Samir Shrestha , Sudarshan Tiwari , Axel Klar , Steffen Hardt

In this paper, we consider the capabilities of the Boltzmann equation with the Shakhov and ellipsoidal models for the collision term to capture the characteristics of rarefied gas flows. The benchmark is performed by comparing the results…

Computational Physics · Physics 2020-07-21 Victor E. Ambrus , Felix Sharipov , Victor Sofonea

We prove existence of weak solutions for a diffuse interface model for the flow of two viscous incompressible Newtonian fluids in a bounded domain by allowing for a degenerate mobility. The model has been developed by Abels, Garcke and…

Analysis of PDEs · Mathematics 2015-06-11 Helmut Abels , Daniel Depner , Harald Garcke

In this paper, a fractional step lattice Boltzmann method is proposed to model two-phase flows with large density differences by solving Cahn-Hilliard phase-field equation and the incompressible Navier-Stokes equations.In order to maintain…

Fluid Dynamics · Physics 2018-12-07 Chunhua Zhang , Zhaoli Guo , Yibao Li