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Differentially weighted direct simulation monte carlo method for particle collision in gas-solid flows

Particuology 2015年第4期13卷 135-145页

作者： Yongxiang He Haibo Zhao Haoming Wang Chuguang Zheng State Key Laboratory of Coal Combustion Huazhong University of Science and Technology

In gas-solid flows, particle-particle interaction （typical, particle collision） is highly significant, despite the small particles fractional volume. Widely distributed polydisperse particle population is a typical characteristic during dynamic evolution of particles （e.g., agglomeration and fragmentation） in spite of their initial monodisperse particle distribution. The conventional direct simulation monte carlo （DSMC） method for particle collision tracks equally weighted simulation particles, which results in high statistical noise for particle fields if there are insufficient simulation particles in less-populated regions. In this study, a new differentially weighted DSMC （DW-DSMC） method for collisions of particles with different number weight is proposed within the framework of the general Eulerian-Lagrangian models for hydrodynamics. Three schemes （mass, momentum and energy conservation） were developed to restore the numbers of simulation particle while keeping total mass, momentum or energy of the whole system unchanged respectively. A limiting case of high-inertia particle flow was numerically simulated to validate the DW-DSMC method in terms of computational precision and efficiency. The momentum conservation scheme which leads to little fluctuation around the mass and energy of the whole system performed best. Improved resolution in particle fields and dynamic behavior could be attained simultaneously using DW-DSMC, compared with the equally weighted DSMC. Meanwhile, computational cost can be largely reduced in contrast with direct numerical simulation.

关键词： direct simulation monte carlo Differentially weighted method Gas-solid flow Particle-particle collision Four-way coupling

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Convergence Detection in direct simulation monte carlo Calculations for Steady State Flows

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Communications in Computational Physics 2011年第9期10卷 807-822页

作者： Jonathan M.Burt Iain D.Boyd U.S.Air Force Research Laboratory Wright-Patterson Air Force BaseOH 45433USA Department of Aerospace Engineering University of Michigan1320 Beal AvenueAnn ArborMI 48109USA

A new criterion is presented to detect global convergence to steady state,and to identify local transient characteristics,during rarefied gas flow simulations performed using the direct simulation monte carlo(DSMC)*** deterministic computational fluid dynamics(CFD)schemes,DSMC is generally subject to large statistical scatter in instantaneous flow property evaluations,which prevents the use of residual tracking procedures as are often employed in CFD ***,reliable prediction of the time to reach steady state is necessary for initialization of DSMC sampling *** currently used in DSMC to identify steady state convergence are usually insensitive to weak transient behavior in small regions of relatively low density or recirculating *** proposed convergence criterion is developed with the goal of properly identifying such weak transient behavior,while adding negligible computational expense and allowing simple implementation in any existing DSMC *** of the proposed technique over existing convergence detection methods are demonstrated for representative nozzle/plume expansion flow,hypersonic blunt body flow and driven cavity flow problems.

关键词： monte carlo methods particle methods direct simulation monte carlo

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Rarefied gas effect in hypersonic shear flows

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Acta Mechanica Sinica 2021年第1期37卷 2-17,I0002页

作者： Jie Chen Heng Zhou Laboratory of High-speed Aerodynamics Tianjin UniversityTianjin300072China

Recently,as aerodynamics was applied to flying vehicles with very high speed and flying at high altitude,the numerical simulation based on the Navier-Stokes(NS)equations was found that cannot correctly predict certain aero-thermo-dynamic properties in a certain range of velocity and altitude while the Knudsen number indicates that the flow is still in the continuum *** first noted by Zhou and Zhang(Science in China,2015),the invalidity of NS equations for such flows might be attributed to an non-equilibrium effect originating from the combined effects of gas rarefaction and strong shear in the boundary-layer *** this paper,we present the scope,physical concept,mathematical model of this shear non-equilibrium effect in hypersonic flows,as well as the way of considering this effect in conventional computational fluid mechanics(CFD)for engineering *** hypersonic flows over sharp bodies and blunt bodies are analyzed by the proposed new continuum model,named direct simulation monte carlo(DSMC)data-improved Navier-Stokes(DiNS)model.

关键词： Rarefied gas effect Hypersonic shear flow Aerodynamics properties direct simulation monte carlo Continuum model

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Employing Per-Component Time Step in DSMC simulations of Disparate Mass and Cross-Section Gas Mixtures

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Communications in Computational Physics 2013年第8期14卷 703-721页

作者： Roman V.Maltsev 8-22 KoltsovoNovosibirsk630559Russia

A new approach to simulation of stationary flows by direct simulation monte carlo method is *** idea is to specify an individual time step for each component of a gas *** approach consists of modifications mainly to collision phase simulation and recommendations on choosing time step *** allows lowering the demands on the computational resources for cases of disparate collision diameters of molecules and/or disparate molecular *** are cases important e.g.,in vacuum deposition *** tests of the new approach are ***,the usage of new approach is demonstrated on a problem of silver nanocluster diffusion in argon carrier gas under conditions of silver deposition experiments.

关键词： direct simulation monte carlo time step disparate masses gas mixture nanoclusters

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Boosting the convergence of low-variance DSMC by GSIS

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Advances in Aerodynamics 2023年第1期5卷 186-211页

作者： Liyan Luo Qi Li Lei Wu Department of Mechanics and Aerospace Engineering Southern University of Science and TechnologyShenzhen 518055China

The low-variance direct simulation monte carlo(LVDSMC)is a powerful method to simulate low-speed rarefied gas ***,in the near-continuum flow regime,due to limitations on the time step and spatial cell size,it takes plenty of time to find the steady-state *** we remove these deficiencies by coupling the LVDSMC with the general synthetic iterative scheme(GSIS)which permits the simulation at the hydrodynamic scale rather than the much smaller kinetic *** a proof of concept,we propose the stochastic-deterministic coupling method based on the Bhatnagar-Gross-Krook kinetic ***,macroscopic synthetic equations are derived exactly from the kinetic equation,which not only contain the Navier-Stokes-Fourier constitutive relation,but also encompass the higher-order terms describing the rarefaction ***,the high-order terms are extracted from LVDSMC and fed into synthetic equations to predict the macroscopic properties which are closer to the steady-state solution than ***,the state of simulation particles in LVDSMC is updated to reflect the change of macroscopic *** a result,the convergence to steady state is greatly accelerated,and the restrictions on cell size and the time step are *** conduct the Fourier stability analysis and simulate several canonical rarefied gas flows to demonstrate the advantages of LVDSMC-GSIS:when the Knudsen number is lower than 0.1,it can use the grid size about 10 times larger than that in traditional DSMC,and it can reduce the computational cost by two orders of magnitude in the flow regime.

关键词： Rarefied gas dynamics direct simulation monte carlo General synthetic iterative scheme Multiscale simulation

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Convergence ofADistributional monte carlo Method for the Boltzmann Equation

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Advances in Applied Mathematics and Mechanics 2012年第1期4卷 102-121页

作者： Christopher R.Schrock Aihua W.Wood Department of Mathematics and Statistics Air Force Institute of TechnologyWright-Patterson AFBOH 45433USA

direct simulation monte carlo(DSMC)methods for the Boltzmann equation employ a point measure approximation to the distribution function,as simulated particles may possess only a single *** representation limits the method to converge only weakly to the solution of the Boltzmann *** kernel density estimation we have developed a stochastic Boltzmann solver which possesses strong convergence for bounded and L∞solutions of the Boltzmann *** is facilitated by distributing the velocity of each simulated particle instead of using the point measure approximation inherent to *** propose that the development of a distributional method which incorporates distributed velocities in collision selection and modeling should improve convergence and potentially result in a substantial reduction of the variance in comparison to DSMC *** this end,we also report initial findings of modeling collisions distributionally using the Bhatnagar-Gross-Krook collision operator.

关键词： direct simulation monte carlo rarefied gas dynamics Boltzmann equation convergence proof

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