The Simulation On Transfer Process And Application Research On Porous Medium Using Lbm

As a mesoscopic method,Lattice Boltzmann Method(LBM)has its unique advantages,such as intrinsic parallelism,simple solution for complex solid boundaries and programming simplicity.It is widely used in microscale flow and heat transfer,porous media,biological fluids,magnetic fluid,nano-fluid,multiphase flow,fuel cell and other fields,and provides a new idea for studying mechanism of various complex phenomenon.But by now LBM has some deficiencies and gaps still in the application of flow and heat transfer in laminar confined impinging jet flow and random porous media,which needs further improvement and development.Therefore,this paper makes positive attempts in two above-mentioned aspects by using LMB.This provides new enlightenments for deep understanding of there issues,meanwhile,it lays a good fundation for subsequent research.In summary,the highlights and main works of this paper includes:(1)As for the study of four circular cylinders,the detailed calculation of square and diamond arrangement reveals the influence of Re number and spacing ratio L/D on flow pattern,drag coefficient,lift coefficient and Nu number.Firstly,the paper studies the flow and stress characteristics,the results show that the flow pattern transforms at different Re number corresponding to different L/D.When the follow pattern changes,the average drag coeff-icient and average lift coefficient varies abruptly.These conclusions are consistent with the reported results.However,only a few studies have been conducted on heat transfer,so the paper have been deeply studied this aspect.The results show that Nu number rapidly increases with Re number.When flow pattern transformation occurs with an increase in L/D,the Nu number increase sharply.For the same flow pattern,Nu changes little even if L/D increases.These works provide a foundation for the study of flow and heat transfer in random porous media.(2)As for the study of impinging jet flow,the paper reveals the effect of Re numbers and jet-impingement surface distance ratio(H/W)on the flow and temperature fields.The traditional simulation results of impinging jet flows are of great dependence on selected turbulence model.Instead,in this paper the LBM is adopted,which avoids the determination of empirical parameters.The results show that the flow fileds changes from stable structure to unstable structure with the increase of Re number.The flow pattern transforms at greater H/W corresponding to smaller critical Re number.The stagnation Nusselt number decreases with the increasing of H/W and decreasing of Re number.Re numbers has more significant effect on heat transfer characteristics between the two parameters.In addition,the paper studies laminar confined impinging jet on cylinder and results shown that the Nusselt number decreases with the increasing of?from 0°to 90°,and increased with the increasing of?from 90°to 135°.These works verify that LBM can accurately simulate the strong swirling flow.(3)For the study of random porous media,the effect of randomness of porous structure,particle sizes,and particle shapes on flow characteristics are sutied.(a)Previous studies proposed many different permeability correlations on porous media,the great difference of porosity on permeability fully proves the influence of complex porous structure.In this paper,the artificial generation besed on process of reconstruction technique is employed to generate random porous media and discusses the flow fields inside porous structure.The results indicate that the permeability for different particles locations is unequal even with the same number and size of particles,so the effect of randomness of porous structure requires special attention.For 2-D porous media,a new relation on permeability is proposed in this paper for random porous medium composed of Gaussian distributed circular cylinders.In additin,new formulation on coefficient b Den is applied to the Forchheimer equation.For 3-D porous media,The paper studies the effect of particle sizes and particle shape.Results show that normalized permeability increased when the classes of particle sizes increase.If the class increases to five,then permeability cannot continue to increase.The normalized permeability of the sphere is higher than that of the cube,mean while,Research contents extend to the case in which the cube length(a)is less than the cube height(b).(b)Through extensive literature on access,it is found that the heat transfer coefficient correlations vary widely in different porous media.There are even conflicting conclusions.Based on this conclusion,this paper discusses the temperature fields inside porous structure.The results show that the Nu number for different particle locations is unequal even with the same number and size of particles,so the effect of randomness of porous structure on heat transfer is unnegligible.For 2-D porous media,a general set of heat transfer correlations is proposed when the effect of porosity is considered.For 3-D porous media,the paper studies the effect of particle sizes and particle shapes.Normalized permeability increases and the Nu number decreases when the level of particle size increases.When the level increases to five,the normalized permeability increases and the Nusselt number ceases to increase.Furthermore,the effect of porosity for the porous structure with the least particle size level on the Nu is the most significant.For the porous structure with the same size distribution but different shape,the increase in amplitude of Nu for cubic particles is larger than that of spherical particles.In short,the research work in this paper is of guiding significance for understanding the flow and heat transfer characteristics of microscale impinging jet flow and random porous media.These studies not only have important practical engineering value,but also expand the research range of LBM in these fields.