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This work presents the application of density-based topology optimisation to the design of three-dimensional heat sinks cooled by natural convection. The governing equations are the steady-state incompressible Navier-Stokes equations…

Fluid Dynamics · Physics 2018-09-14 Joe Alexandersen , Ole Sigmund , Niels Aage

Reactive flows for rarefied gas mixtures involve a multi-scale transport characterized by particle collisions and free streaming, and non-equilibrium physics containing multi-species interactions, and chemical non-equilibrium. These flows…

Fluid Dynamics · Physics 2024-12-16 Yufeng Wei , Junzhe Cao , Kun Xu

We present a fully-coupled, implicit-in-time framework for solving a thermodynamically-consistent Cahn-Hilliard Navier-Stokes system that models two-phase flows. In this work, we extend the block iterative method presented in Khanwale et…

Due to limited possibilities of experimental investigations for non-equilibrium gas flows, numerical results are of highest interest. Although the well-established Direct Simulation Monte Carlo (DSMC) method achieves highly accurate…

Computational Physics · Physics 2025-02-04 Franziska Hild , Marcel Pfeiffer

For the simulations of unsteady flow, the global time step becomes really small with a large variation of local cell size. In this paper, an implicit high-order gas-kinetic scheme (HGKS) is developed to remove the restrictions on the time…

Numerical Analysis · Mathematics 2024-03-04 Yaqing Yang , Liang Pan , Kun Xu

While various phase-field models have recently appeared for two-phase fluids with different densities, only some are known to be thermodynamically consistent, and practical stable schemes for their numerical simulation are lacking. In this…

The stochastic particle method based on Bhatnagar-Gross-Krook (BGK) or ellipsoidal statistical BGK (ESBGK) model approximates the pairwise collisions in the Boltzmann equation using a relaxation process. Therefore, it is more efficient to…

Computational Physics · Physics 2018-08-14 Fei Fei , Jun Zhang , Jing Li , ZhaoHui Liu

In this paper, a unified gas kinetic scheme with adaptive velocity space (AUGKS) for multiscale flow transport will be developed. In near-equilibrium flow regions, particle distribution function is close to the Chapman-Enskog expansion and…

Computational Physics · Physics 2018-02-15 Tianbai Xiao , Kun Xu , Qingdong Cai

This paper presents an incomplete Octree mesh implementation of the Shifted Boundary Method (Octree-SBM) for multiphysics simulations of coupled flow and heat transfer. Specifically, a semi-implicit formulation of the thermal Navier-Stokes…

We propose a new family of high order staggered semi-implicit discontinuous Galerkin (DG) methods for the simulation of natural convection problems. Assuming small temperature fluctuations, the Boussinesq approximation is valid and the flow…

Computational Physics · Physics 2019-12-05 Saray Busto , Maurizio Tavelli , Walter Boscheri , Michael Dumbser

A computationally accurate and efficient numerical method under a unified framework is crucial to various multi-scale scientific and engineering problems. So far, many numerical methods have encountered various challenges in efficiently…

Fluid Dynamics · Physics 2023-03-21 Rui Zhang , Sha Liu , Jianfeng Chen , Chengwen Zhong , Congshan Zhuo

For more than 150 years the Navier-Stokes equations for thermodynamically quasi-equilibrium flows have been the cornerstone of modern computational fluid dynamics that underpins new fluid technologies. However, the applicable regime of the…

Fluid Dynamics · Physics 2012-01-11 Jianping Meng , Nishanth Dongari , Jason M. Reese , Yonghao Zhang

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

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

Fluid dynamic equations are valid in their respective modeling scales. With a variation of the modeling scales, theoretically there should have a continuous spectrum of fluid dynamic equations. In order to study multiscale flow evolution…

Numerical Analysis · Mathematics 2017-12-21 Chang Liu , Kun Xu , Quanhua Sun , Qingdong Cai

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

For the two-layer shallow water equations, a high-order compact gas-kinetic scheme (GKS) on triangular mesh is proposed. The two-layer shallow water equations have complex source terms in comparison with the single layer equations. The main…

Numerical Analysis · Mathematics 2023-06-08 Fengxiang Zhao , Jianping Gan , Kun Xu

Discrete unified gas-kinetic scheme (DUGKS) is a multi-scale numerical method for flows from continuum limit to free molecular limit, and is especially suitable for the simulation of multi-scale flows, benefiting from its multi-scale…

Computational Physics · Physics 2025-04-07 Jianfeng Chen , Sha Liu , Yong Wang , Chengwen Zhong

The non-equilibrium gas dynamics is described by the Boltzmann equation, which can be solved numerically through the deterministic and stochastic methods. Due to the complicated collision term of the Boltzmann equation, many kinetic…

Computational Physics · Physics 2021-02-03 Xiaocong Xu , Yipei Chen , Kun Xu

Unified gas kinetic scheme (UGKS) is an asymptotic preserving scheme for the kinetic equations. It is superior for transition flow simulations, and has been validated in the past years. However, compared to the well known discrete ordinate…

Fluid Dynamics · Physics 2016-08-31 Songze Chen , Zhaoli Guo , Kun Xu