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This paper introduces a time-domain harmonic balance unified gas-kinetic scheme (HB-UGKS) designed to simulate temporally periodic flows across all Knudsen regimes. The harmonic balance approach reformulates the periodic problem into a…

Fluid Dynamics · Physics 2026-05-06 Yuze Zhu , Hangkong Wu , Yufeng Wei , Kun Xu

This paper presents a comprehensive numerical framework for simulating radiation-plasma systems. The radiative transfer process spans multiple flow regimes due to varying fluid opacity across different regions, necessitating a robust…

Astrophysics of Galaxies · Physics 2025-12-24 Mingyu Quan , Kun Xu

Rarefied gas effects are of critical importance for the aerodynamic performance of hypersonic vehicles operating at high altitudes. In these scenarios, conventional computational fluid dynamics (CFD) solvers break down as the linear…

Fluid Dynamics · Physics 2026-05-25 Wenpei Long , Junzhe Cao , Yue Zhang , Kun Xu

The gas dynamics under external force field is essentially associated with multiple scale nature due to the large variations of density and local Knudsen number. Single scale fluid dynamic equations, such as the Boltzmann and Navier-Stokes…

Fluid Dynamics · Physics 2017-10-31 Tianbai Xiao , Kun Xu , Qingdong Cai , Tiezheng Qian

During the past decades, the numerical methods based on Navier-Stokes (N-S) equations and direct simulation Monte Carlo (DSMC) methods have been proved effective in simulating flows in the continuum and rarefied regimes, respectively.…

Fluid Dynamics · Physics 2024-09-24 Sirui Yang , Sha Liu , Junzhe Cao , Chengwen Zhong

This paper presents a novel methodology for the direct numerical modeling and simulation of turbulent flows. The kinetic model equation is firstly extended to turbulent flow with the account of coupled evolution of kinetic, thermal, and…

Computational Physics · Physics 2025-03-11 Xiaojian Yang , Kun Xu

Nonequilibrium flows have been frequently encountered in various aerospace engineering applications. To understand nonequilibrium physics, multiscale effects, and the dynamics in these applications, an effective and reliable multiscale…

Fluid Dynamics · Physics 2024-07-23 Wenpei Long , Yufeng Wei , Kun Xu

The unified gas kinetic scheme (UGKS) is a direct modeling method based on the gas dynamical model on the mesh size and time step scales. With the implementation of particle transport and collision in a time-dependent flux function, the…

Computational Physics · Physics 2017-10-25 Yajun Zhu , Chengwen Zhong , Kun Xu

In recent years, non-equilibrium flows have gained significant attention in aerospace engineering and micro-electro-mechanical systems. The unified gas-kinetic scheme (UGKS) follows the methodology of direct modeling to couple particle…

Computational Physics · Physics 2024-12-10 Yue Zhang , Yufeng Wei , Wenpei Long , Kun Xu

This paper aims at the simulation of multiple scale physics in the system of radiation hydrodynamics. The system couples the fluid dynamic evolution equations with the radiative heat transfer. The coupled system is solved by the gas-kinetic…

Computational Physics · Physics 2019-09-12 Wenjun Sun , Song Jiang , Kun Xu , Guiyu Cao

A standard artificial compression (AC) method for incompressible flow is $$ \frac{u_{n+1}^{\varepsilon }-u_{n}^{\varepsilon }}{k}+u_{n+1}^{\varepsilon }\cdot \nabla u_{n+1}^{\varepsilon }+{\frac{1}{2}}u_{n+1}^{\varepsilon }\nabla \cdot…

Numerical Analysis · Mathematics 2019-05-01 Robin Ming Chen , William Layton , Michael McLaughlin

This paper presents an implicit method for the discrete unified gas-kinetic scheme (DUGKS) to speed up the simulations of the steady flows in all flow regimes. The DUGKS is a multi-scale scheme finite volume method (FVM) for all flow…

Fluid Dynamics · Physics 2018-10-18 Dongxin Pan , Chengwen Zhong , Congshan Zhuo

In this paper, we present a high-order unified gas-kinetic scheme (UGKS) using the weighted essentially non-oscillatory with adaptive-order (WENO-AO) method for spatial reconstruction and the two-stage fourth-order scheme for time…

Computational Physics · Physics 2022-12-12 Gyuha Lim , Yajun Zhu , Kun Xu

The unified gas kinetic scheme (UGKS) was initially designed to address multiscale challenges in rarefied gas dynamics and then extended to radiative transfert theory, as described by BGK like relaxation models. In this work, we extend its…

Numerical Analysis · Mathematics 2025-07-08 Julien Mathiaud , Luc Mieussens , Nicolas Crouseilles

In this study, the Vlasov-Poisson equation with or without collision term for plasma is solved by the unified gas kinetic scheme (UGKS). The Vlasov equation is a differential equation describing time evolution of the distribution function…

Computational Physics · Physics 2018-10-18 Dongxin Pana , Chengwen Zhong , Congshan Zhuo , Wei Tan

In order to further enhance the computational efficiency of the implicit unified gas-kinetic scheme (IUGKS, JCP 315 (2016) 16-38) for multi-scale flow simulation, a two-step IUGKS is proposed in this paper. The multiscale solution of the…

Computational Physics · Physics 2021-05-04 Xiaocong Xu , Yajun Zhu , Chang Liu , Kun Xu

Solving the Bhatnagar-Gross-Krook (BGK) equation with a stochastic particle approach enables efficient and flexible simulations of flows in the transition regime, between continuum and free molecular flow. However, the usual first-order…

Fluid Dynamics · Physics 2024-12-02 Marcel Pfeiffer , Félix Garmirian , Tobias Ott

In this paper, authors focus effort on improving the conventional discrete velocity method (DVM) into a multiscale scheme in finite volume framework for gas flow in all flow regimes. Unlike the typical multiscale kinetic methods unified…

Computational Physics · Physics 2020-03-24 Ruifeng Yuan , Sha Liu , Chengwen Zhong

The gas-kinetic scheme (GKS) provides high computational efficiency and accuracy for continuum flow simulations but is unable to reliably capture rarefaction effects. In contrast, although the discrete velocity method (DVM) is better suited…

Fluid Dynamics · Physics 2026-05-08 Hangkong Wu , Yuze Zhu , Yajun Zhu , Kun Xu

The discrete unified gas kinetic scheme (DUGKS) is a finite-volume scheme with discretization of particle velocity space, which combines the advantages of both lattice Boltzmann equation (LBE) method and unified gas kinetic scheme (UGKS)…

Fluid Dynamics · Physics 2014-11-25 Chen Wu , Baochang Shi , Zhenhua Chai , Peng Wang