Lattice Boltzmann Simulation Of Fluid-thermal Coupled In A Cavity With Electromagnetic Fields

Electro-Thermo-Convection(ETC)refers to the fluid flow and heat transfer problems caused by Coulomb force and buoyancy force.Due to the coupling of multiple physical fields such as electric fields,temperature field and flow field,and it can realize the control of system flow and heat transfer,it has become a problem that needs to be solved urgently in many actual industrial production.The Lattice Boltzmann method has the advantages of clear physical images,easyto-handle boundary conditions,simple programming and good parallel performance.It is suitable for solving multi-physical coupling problems.In the paper,a unified form of LBM is used to carry out numerical simulation on the ETC under the charge inj ection mechanism.The governing equations can be treated in dimensionless forms by introducing the dimensionless parameters,and establish the lattice Boltzmann model of each physical field.(1)The LBM method is used to investigate the problem of ETC in the cavity under the non-uniform temperature boundary condition.The influences of two different temperature boundary conditions,the sinusoidal temperature boundary and the uniform temperature boundary,are analyzed emphatically.The specific parameters of the sinusoidal temperature distribution function:amplitude A,initial phase ?,and fluctuation period N are numerically studied on the effect of ETC heat transfer mechanism,and the ETC problem under different working conditions is analyzed.The results show that:compared with uniform temperature heating method,the sinusoidal temperature boundary has higher heat transfer performance,and the difference gradually weakens with the increase of Tvalues;With increasing T,the system changed from one stable state to another,the fluid flow intensity in the cavity increased,and the heat transfer significantly improved;In addition,the parameters of sinusoidal temperature distribution function have a significant influence on the flow and heat transfer of ETC problem.The increase of amplitude A of the sinusoidal temperature can enhance the heat transfer in the cavity,but it showed two different trends.When A<0.6,the performance of flow and heat transfer was not improved much by the increase of A.When A>0.6,heat transfer performance increased rapidly with increasing A value,indicating strong flow and heat transfer of the ETC system.With increasing initial phase ?,the heat transfer of the system was also increased,and the best heat transfer behavior was shown in the case of ?=90°.In the paper,the Nonorthogonal multiple-relaxation time lattice Boltzmann method(MRT-LBM)is used to investigate the laminar mixed convection in porous cavity with an isothermally heated block.Firstly,a non-orthogonal MRT-LBM model with dual coupling distribution of flow field and temperature field is established.The different arrangements of cold sources,different lid-driven cavities and Richardson number is studied.We also investigate three different convection methods:natural convection,mixed convection and forced convection.The results show that with increasing Ri,the number of vortices in the cavity changes differently corresponding to different cold source locations.The different cold source arrangements show different heat transfer performance in the cavity.The driving position and direction of lid-driven have obvious effects on the flow and heat transfer in the cavity.The right-moving top and bottom walls exhibits best heat transfer characteristic than other three cases when Ri ?1,and the case of top and bottom walls moves in the opposite directions has best heat transfer performance than other three cases when Ri>1.When the cold sources are arranged on the upper wall of the cavity,it shows better heat transfer performance.In addition,the flow and heat transfer in porous media are often affected by the magnetic field.The flow and heat transfer process of the magnetic fluid can be controlled by the magnetic field.In this paper,the non-orthogonal MRT-LBM method is used to study the characteristics of nanofluid flow and heat transfer in porous media under an external magnetic field.The influence of the nanoparticle volume fraction,the magnetic field intensity(Ha),the porosity of porous media and other parameters are discussed,which further perfects the study of magnetic fluids.The results show that the heat transfer performance in the cavity decreases significantly with the increase of Ha number.The average Nu number decreases more obviously with increasing Ha number under high Rayleigh number.The Lorentz force has an inhibitory effect on the heat transfer of nanofluids in the cavity due to the presence of the magnetic field,and this inhibitory effect is more significant under high Rayleigh number.