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工程与科学中的计算机建模(英文) 2024年第1期138卷 273-299页

作者： Siham Hammid Khatir Naima Omolayo M.Ikumapayi Cheikh Kezrane Abdelkrim Liazid Jihad Asad Mokdad Hayawi Rahman Farhan Lafta Rashid Naseer Ali Hussien Younes Menni Laboratory of Development in Mechanics and Materials(LDMM) Zian Achour UniversityDjelfaPB 3117Algeria Department of Technology University Center Salhi Ahmed Naama(Ctr.Univ.Naama)P.O.Box 66Naama45000Algeria Department of Mechanical and Mechatronics Engineering Afe Babalola University Ado Ekiti360101Nigeria Departement of Physics Faculty of ScienceAbou Bekr Belkaid UniversityTlemcen13000Algeria Department of Physics Faculty of Applied SciencesPalestine Technical University-KadoorieTulkarmPalestine Aeronautical Technical Engineering Al-Farahidi UniversityBaghdad10011Iraq Mechanical Engineering Department University of KerbalaKarbala56001Iraq Information and Communication Technology Research Group Scientific Research CenterAl-Ayen UniversityThi-QarIraq National University of Science and Technology Dhi QarIraq

The objective of this investigation is to assess the effect of obstacles on numerical heat transfer and fluid flow momentum in a rectangular microchannel(MC).Two distinct configurations were studied:one without obstacles and the other with alternating obstacles placed on the upper and lower *** research utilized the thermal lattice Boltzmann method(LBM),which solves the energy and momentum equations of fluids with the BGK approximation,implemented in a Python coding *** jump and slip velocity conditions were utilized in the simulation for the MC and extended to all obstacle *** study aims to analyze the rarefaction effect,with knudsen numbers(Kn)of 0.012,0.02,and *** outcomes indicate that rarefaction has a significant impact on the velocity and temperature *** presence of nine obstacles led to slower fluid movement inside the microchannel MC,resulting in faster cooling at the *** MCs with obstacles,the rarefaction effect plays a crucial role in decreasing the Nusselt number(Nu)and skin friction coefficient(Cf).Furthermore,the study demonstrated that the obstacles played a crucial role in boosting fluid flow and heat transfer in the *** findings suggest that the examined configurations could have potential applications as cooling technologies in micro-electro-mechanical systems and microdevice applications.

关键词： Microfluid rarefied flow LBM microchannel knudsen number numerical simulation

Effects of thermophoresis on Brownian coagulation of spherical particles over the entire particle size regime

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Particuology 2022年第8期20卷 8-17页

作者： Kaiyuan Wang Pei Wang Suyuan Yu Institute of Applied Physics and Computational Mathematics Bejing 100094.China Center forCombustionEergy.Key Laboratory for Thermal Science and Power Engineering of Ministry of Education Department of Energyand PowerEngineeringTsinghua UniversityBejing 100084.China Smoore International Holdings Ltd.Shenzhen 518102 China

In many energy and combustion *** experience large temperature gradients,which can affect the coagulation process due to *** study presents a rigorous theory of thermophoretically modified Brownian coagulation in the entire particle size *** theoretical derivations are based on the kinetictheory forthe free-molecular regime and the harmonic mean method for the transition *** coagulation kernels in different size regimes can be expressed as the basic Brownian coagulation kernel times an enhancement factor,The enhancement factor represents the coagulationrate enhancement induced by thermophoresis and is a function of specific dimensionless *** on the enhancement factor,the thermophoretic enhancement effects on particle coagulation are further analyzed under a wide range of gas and particle *** results show that thermophoretic enhancement effects are ignorable in the free-molecular regime,but need to be considered in the continuum regime and the transition *** addition,the enhancement effects increase significantly with increase of gas temperature and temperature gradient while decrease with increase of gas *** present study can improve understanding ofthermophoretic effects on Brownian coagulation in the entire size regime and provide a useful tool to calculate the coagulation rates in presence of thermophoresis.

关键词： Thermophoresis Brownian coagulation Enhancement factor knudsen number

Flow instability of nanofuilds in jet

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Applied Mathematics and Mechanics(English Edition) 2015年第2期36卷 141-152页

作者： Yi XIA Jianzhong LIN Fubing BAO T.L.CHAN Department of Mechanics State Key Laboratory of Fluid Power Transmission and ControlZhejiang University Institute of Fluid Mechanics China Jiliang University Department of Mechanical Engineering The Hong Kong Polytechnic University

The flow instability of nanofluids in a jet is studied numerically under various shape factors of the velocity profile, Reynolds numbers, nanoparticle mass loadings,knudsen numbers, and Stokes numbers. The numerical results are compared with the available theoretical results for validation. The results show that the presence of nanoparticles enhances the flow stability, and there exists a critical particle mass loading beyond which the flow is stable. As the shape factor of the velocity profile and the Reynolds number increase, the flow becomes more unstable. However, the flow becomes more stable with the increase of the particle mass loading. The wavenumber corresponding to the maximum of wave amplification becomes large with the increase of the shape factor of the velocity profile, and with the decrease of the particle mass loading and the Reynolds number. The variations of wave amplification with the Stokes number and the knudsen number are not monotonic increasing or decreasing, and there exists a critical Stokes number and a knudsen number with which the flow is relatively stable and most unstable,respectively, when other parameters remain unchanged. The perturbation with the first azimuthal mode makes the flow unstable more easily than that with the axisymmetric azimuthal mode. The wavenumbers corresponding to the maximum of wave amplification are more concentrated for the perturbation with the axisymmetric azimuthal mode.

关键词： nanoparticle-laden jet flow hydrodynamic instability Stokes number knudsen number particle mass loading

Analytical method of nonlinear coupled constitutive relations for rarefied non-equilibrium flows

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Chinese Journal of Aeronautics 2021年第2期34卷 136-153页

作者： Zhiqiang HE Zhongzheng JIANG Huangwei ZHANG Weifang CHEN School of Aeronautics and Astronautics Zhejiang UniversityHangzhou 310027China Department of Mechanical Engineering National University of SingaporeSingapore 117576Singapore

It is well known that Navier-Stokes equations are not valid for those high-knudsen and high-Mach flows, in which the local thermodynamically non-equilibrium effects are dominant. To extend the non-equilibrium describing the ability of macroscopic equations, Nonlinear Coupled Constitutive Relation(NCCR) model was developed from Eu’s generalized hydrodynamic equations to substitute linear Newton’s law of viscosity and Fourier’s law of heat conduction in conservation laws. In the NCCR model, how to solve the decomposed constitutive equations with reasonable computational cost is a key ingredient of this scheme. In this paper, an analytic method is proposed firstly. Compared to the iterative procedure in the conventional NCCR model, the analytic method not only obtains exact roots of the decomposed constitutive polynomials, but also preserves the nonlinear constitutive relations in the original framework of NCCR methods. Numerical tests to assess the efficiency and accuracy of the proposed method are conducted for argon shock structures, Couette flows, two-dimensional hypersonic flows over a cylinder and threedimensional supersonic flows over a three-dimensional sphere. These superior advantages of the current method are expected to render itself a powerful tool for simulating the hypersonic rarefied flows and microscale flows of high knudsen number for engineering applications.

关键词： knudsen number Microscale flow Non-equilibrium Nonlinear constitutive relations Rarefied gas

Lattice Boltzmann Flow Simulation in a Combined Nanochannel

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Advances in Applied Mathematics and Mechanics 2010年第5期2卷 609-625页

作者： Kazuhiko Suga Susumu Takenaka Takahiko Ito Masayuki Kaneda Department of Mechanical Engineering Osaka Prefecture UniversitySakai 599-8531Japan

The widely used micro-flow wall-boundary conditions for lattice Boltzmann method(LBM)are evaluated in a force driven combined nanochannel *** flow field consists of a two-dimensional nanochannel(mother channel)of an infinite length having flat plates of a finite length *** flat plate is set above the bottom wall of the nanochannel with a narrow *** flow,thus,develops through this narrow gap(narrower channel)and the other side of the plate(wide gap).The knudsen number based on the mother channel height is Kn=0.14 whereas the characteristic knudsen number in the narrower channel is *** obtain the reference data,the molecular dynamics(MD)simulation is performed with a fully diffusive wall *** LBMs are based on the lattice BGK model and with the bounce-back/specular reflection(BSBC)and the diffuse scattering(DSBC)wall boundary *** relaxation time is modified to include sensitivity to *** DSBC shows generally satisfactory results in the test flow cases including fully developed force driven Poiseuille flows,where the BSBC performs worse at Kn>0.5 with a fixed bridge coefficient of b=*** results in its overprediction of the flow rate in the narrower channel region since the characteristic knudsen number there is *** MD simulation suggests that the flow develops gradually through the narrower channel region though all the LBM predictions show almost instant flow *** fact suggests that the relaxation time model needs to have more sensitivity to the locally defined *** discussions of the BSBC with a different set of models suggest that the regularization process is required for predicting complex nanoscale flows.

关键词： Lattice Boltzmann method knudsen number molecular dynamics simulation nanochannel wall boundary condition slippage velocity

Gas Flow Through Square Arrays of Circular Cylinders with Klinkenberg Effect:A Lattice Boltzmann Study

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Communications in Computational Physics 2010年第10期8卷 1052-1073页

作者： Zhenhua Chai Baochang Shi Zhaoli Guo Jianhua Lu School of Mathematics and Statistics Huazhong University of Science and TechnologyWuhan430074China State Key Laboratory of Coal Combustion Huazhong University of Science and TechnologyWuhan430074China

It is well known that,as non-continuum gas flows through microscale porous media,the gas permeability derived from Darcy law is larger than the absolute permeability,which is caused by the so-called Klinkenberg effect or slippage *** this paper,an effective definition of knudsen number for gas flows through square arrays of circular cylinders and a local boundary condition for non-continuum gas flows are first proposed,and then the multi-relaxation-time lattice Boltzmann equation including discrete effects on boundary condition is used to investigate Klinkenberg effect on gas flow through circular cylinders in square *** results show that the celebrated Klinkenberg equation is only correct for low knudsen number,and secondorder correction to Klinkenberg equation is necessary with the increase of knudsen ***,the present numerical results are also compared to some available results,and in general an agreement between them is observed.

关键词： Klinkenberg effect multi-relaxation-time lattice Boltzmann equation knudsen number Klinkenberg equation

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螺旋流作用下微壳结构动力学特性研究

螺旋流作用下微壳结构动力学特性研究

Shale gas reservoirs: Theoretical, practical and research issues

第十九届全国非线性振动暨第十六届全国非线性动力学和运动稳定性学术会议（NVND2023）

作者：宁文波陈尚陈欣磊李云东

随着微、纳技术的发展,输流微壳(管)被广泛应用于微机电系统、生物医疗、微腔共振器等众多微型设备中。若环流在轴向流动的同时叠加了旋转分量,即为螺旋环流,微热管和微反应器为螺旋环流的典型工程应用。研究螺旋流作用下输流壳的稳定... 详细信息

随着微、纳技术的发展,输流微壳(管)被广泛应用于微机电系统、生物医疗、微腔共振器等众多微型设备中。若环流在轴向流动的同时叠加了旋转分量,即为螺旋环流,微热管和微反应器为螺旋环流的典型工程应用。研究螺旋流作用下输流壳的稳定性和动力学具有重要的理论意义,对该结构的优化设计和安全使用具有重要的工程价值。设若螺旋环流为充分发展的湍流,对其解耦为时均流场和摄动流场。使用时均Navier-Stokes(纳维-斯托克斯)方程和流体连续性方程,建立时均流场的稳态粘性力表达式;使用势流理论和流固耦合边界条件,建立摄动流场的摄动流体力表达式。基于修正的偶应力理论,利用Hamilton原理建立螺旋流作用下输流微壳的动力学方程组。通过把壳体的位移展成行波解,借助Galerkin技术,把动力学方程组离散为常微分方程组,进行输流微壳动力学特性分析。基于上述方法,将重点研究流体的旋转效应对输流微壳失稳的影响、研究流体旋转效应与尺寸效应之间的耦合作用对稳定性的复杂影响,最后,研究流体的粘性效应对稳定性的影响,并与宏观尺度下输流壳的稳定性结果进行比较,探讨流体粘性的作用。

关键词：输流微壳螺旋环流尺寸效应粘性 knudsen number

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Petroleum Research 2016年第1期1卷 10-26页

作者： Roberto Aguilera Schulich School of Engineering University of CalgaryCalgaryCanada

Shale gas reservoirs are found all over the *** endowment worldwide is estimated at 10,000 tcf by the GFREE team in the Schulich School of Engineering at the University of *** shale gas work and production initiated successfully in the Unites States and extended to Canada will have application,with modifications,in several other countries in the ***‘modifications’qualifier is important as each shale gas reservoir should be considered as a research project by itself to avoid fiascos and major financial *** gas reservoirs are best represented by at least quadruple porosity *** of the production obtained from shale reservoirs is dominated by diffusion *** approximate boundary between viscous and diffusion-like flow is estimated with knudsen *** flow is present,for example,when the architecture of the rock is dominated by mega pore throat,macro pore throat,meso pore throat and sometimes micro pore *** flow on the other hand is observed at the nano pore throat *** process speed concept has been used successfully in conventional reservoirs for several ***,the concept discussed in this paper for tight gas and shale gas reservoirs,with the support of core data,has been developed only recently,and permits differentiating between viscous and diffusion dominated *** is valuable,for example,in those cases where the formation to be developed is composed of alternating stacked layers of tight sands and shales,or where there are lateral variations due to facies *** approach to develop the concept of a super-giant shale gas reservoir is presented as well as a description of GFREE,a successful research program for tight *** paper closes with examples of detailed original gas-in-place(OGIP)calculations for 3 North American shale gas reservoirs including free gas in natural fractures and the porous network within the organic matter,gas in the non-organic matter,adsorbed gas,a

关键词： shale gas reservoirs process or delivery speed quadruple porosity model knudsen number pore throat level

Coupled coagulation of aerosol particles at large knudsen and small Peclet numbers

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Progress in Natural Science:Materials International 2001年第2期 16-21页

作者：张连众温景嵩 China Institute of Physics Nankai University Tianjin 300071

At large knudsen number, the medium can be approximated by a molecular system, and the equation for the pair-distribution function is then established. When the Peclet number is small, the matched asymptotic expansions of singular perturbation theory is used to solve the equation of the pair-distribution function. A third-order expansion for the dimensionless coagulation rate (Nusselt number) is thus obtained. Comparison of numeric results of the coagulation rate in a molecular system and that in a continuous medium has shown that the coagulation rate in a molecular system is much larger than that in a continuous medium.

关键词： knudsen number Peclet number aerosol particle singular perturbation coagulation rate.