FLOW-3D多孔介质模型-渗流模型培训讲学.ppt

Click to edit Master title style,Click to edit Master text styles,Second level,Third level,Fourth level,Fifth level,*,FLOW-3D多孔介质模型-渗流模型,Porous components,Require 2 computational cells to adequately resolve,Model object as component if,Significant gradients occur through thickness of material,Material is anisotropic,Porous material may be,Isotropic(e.g.bed of uniform particles),Anisotropic(e.g.tube bundles),Porous baffles,No thickness,reside on cell faces,Best for modeling screens,Drag can be linear or quadratic,Model assumes baffle is saturated,no bubble pressure across,Types of Porous Objects in FLOW-3D,5/14/2025,User Training,Porous Media Modeling,Theory,List of topics,介绍达西定律（,Darcy law,）,介绍,FLOW-3D,拖,曳,力模型,(drag model),介绍饱和多孔介质模型,(the saturated porous media model),介绍拖,曳,力系数与渗透率的关系,(drag coefficient and permeability),如何处理流体在多孔介质中的各向异性,(anisotropy),特征,介绍非饱和多孔介质模型,(the unsaturated porous media model),达西定律（,Darcy Law,）,Q,:units of volume per time(e.g.,m/s),A:cross-sectional area,(P,b,P,a,):the pressure drop,:dynamic viscosity,:the,permeability,of the medium(units of area,e.g.m),L:the length,Darcys Law:Flow rate through porous media is proportional to pressure drop according to:,where,v,=macroscopic(superficial)velocity(,FLOW-3D,computes and reports microscopic velocity),K=intrinsic permeability-may be isotropic or anisotropic(directional),m,=dynamic viscosity,P=fluid pressure,Permeability,Property of the porous material,Represents the average resistance to flow in a control volume,Darcys law represents viscous losses through pores,Applicable when pore Reynolds number Re,p,1,where Re,p,=,Applies well to tightly packed spheres and fibers,Does not represent inertial losses in loosely packed beds,Viscous Drag in Porous Media:Darcys Law,Inertial drag becomes significant when Re,p,exceeds 10,Darcys Law can be extended to include inertial effects,Quadratic drag:Forchheimers Equation,Inertial Losses:Forchheimers Equation,viscous,transitional,inertial,where,r,=fluid density,Understanding,FLOW-3D,sDrag Model,由于流体在多孔介质中受到的很多阻力太小而无法求解，所以用一个均布的阻力系数来计算：,K,表示拖曳力系数，也就是流体在多孔介质中的流动阻力。,Total acceleration,Inertia,Acc.due to press.gradient,Accel.due to viscosity,Accel.due to gravity,Drag effects,V,f,=,Volume fraction(porosity)of computational cell,A,f,=,Diagonal tensor area fractions of cell,N-S,张量方程,Porous material characterized by:,Solid structure permeated by interconnected capillaries,May consist of fibers,particles,open pores,Two types of flow inside porous media,Saturated,Assumes media is already wet,If interface between fluid and air exists,treated as sharp,Unsaturated,Diffuse fluid/air interface-wicking,Hysteresis(filling/draining)effects,Two contributions to fluid drag in porous media,Viscous(Skin Drag),Inertial(Form Drag),Porous Media Flow,Resolve all geometry(FAVOR),Compute pressures and velocities directly from Navier Stokes equations,Useful for characterizing materials,Computationally expensive,Approaches to Modeling Porous Materials,Direct,Volume Averaged,Geometry represented as volume fraction(porosity)open to flow,Assume flow is uniform over cell,Requires some knowledge of material,Porosity,Pressure drop vs velocity,or,Particle/fiber size,Focus of this presentation is the,volume averaged,approach,Saturated Flow,Unsaturated Flow,Interfacial Effects:Capillary Pressure,Generally applies to flow through porous regions filled with water,Air/water interface is sharp,Capillary pressure function of pore diameter,Applies to flow through porous regions which may be wet or dry,Air/water interface is diffuse(wicking),Capillary pressure function of saturation and direction,i.e.filling or draining,Porous media simulation setup steps:,Decide flow type:Saturated,or,Unsaturated,Define porous geometry,Drag Model,3 choices for saturated flow,1 choice for unsaturated flow,Characterize Material,Porosity,Fit drag coefficients,experimental data,compute from fiber/particle size,Setting Up A Porous Media Simulation,Saturated,Unsaturated,Saturated porous media,Useful for situations where there exists a well-defined saturation front with the porous material,Model assumes that saturated regions are separated from“dry”regions by a thin saturation front,Pressure difference across this saturation front is dictated by a user-defined capillary pressure(,P,cap,),d,a,fluid in a pore,s,Concave case(lower pressure in liquid)is assumed to have+ve,P,cap,拖曳力与渗透率关系式,Often confusion arises between Darcy permeability(,)and the drag coefficient(K).The relationship is:,Thus,a material with drag represents 0 permeability,“Drag coefficient”in FLOW-3D output is:,This can vary between 0(infinite drag)and 1(zero drag)and is dimensionless,and,拖曳力系数（,The drag coefficient,）,or,Setting up a problem with saturatedporous media,激活,Porous media,多孔介质物理模型,创建,porous component(s),多孔材料,每一个,component,可以由多个,sub-components,或,STL,文件 来创建更复杂的形状,在每一个,component,需指定孔隙率（,porosity,），毛细管压力（,capillary pressure,）及拖曳系数（,drag coefficients,）,每一个,component,可以设定不同属性,Modeling anisotropic materialswith,FLOW-3D,渗透率（,Permeability,）是具有各向异性的，也就意味着流体的渗透率在每个流动方向都不同。,在,FLOW-3D,软件中，用户可以指定各方向的孔隙率（,porosity,），其可控制各方向的面积比例值（,the area fraction-,A,f,),若设定一个方向的数值比其它两个方向小，那么在该方向流动时开口面积会变小,总的孔隙率设定为三个方向中最大值,Setting anisotropic materialsexample,Suppose we have a sheet-like material where:,Then the porosity in the x,y directions should be set to 0.6(the true porosity),The porosity in the z-direction is set to 0.45(0.61.5/2),The drag coefficient is set according to the higher permeability(3000 s,-1,in this case),x,y,=210,-6,cm,2,z,=1.510,-6,cm,2,Porosity=0.6,Sample:multilayer porous material,Drop is absorbed into three layer porous material,Saturated model used,Porosity,P,cap,adrg,bdrg,Top&bottom layers,50%,610,3,3.510,7,110,5,Middle layer,35%,910,3,510,7,110,5,Permeability ratio for middle layer:,z,/,r,=0.71,0s,0.1s,0.2s,1s,Unsaturated porous media model,With this option,model simulates saturation gradients and varies capillary pressure throughout,Regions with lower saturation predicted to have greater(i.e.more negative)capillary pressure,Model(w/o customization)presumes wetting medium to model fluid,Hysteresis in capillary pressure predicted,Drag is function of saturation(fraction of pore space occupied by fluid),or,Capillary pressure model forunsaturated porous media,Sample curves at left show both filling and draining curves,P,cap,will follow appropriate curve during continuous filling or draining,When region of porous material switches between filling and draining,Pcap will follow scanning curve until it reaches main curve,Draining curve,Filling curve,Sample scanning curves,Defining composites of differentmaterials,As with the saturated porous media models,composites are defined first by creating components,Specifications for capillary pressure curves are made in input file,pcap,namelist must first be created within input file,located between the,scalar,and,bcdata,namelists,Setting up the input file forunsaturated porous media modeling,Create,pcap,namelist,provide global values for,fcmn,fcmx,fpcmx,pcmx,pexp,These will apply to all components by default,Add component-specific values if desired in,obs,namelist,provide values for,ofcmn,ofcmx,ofpcmx,opcmx,opexp,Apply only to specific component,Also,idfit,or,iodfit,parameters control drag function,1 power law function,2 exponent function,实例,:,多个 孔隙率材料的仿真,Component 1,Component 4,Component 5,Component 3,Component 2,Component,pcmx,fpcmx,P,exp,1,110,6,0.15,0.9,2,2.510,5,0.2,0.5,3,510,5,0.05,0.7,4,310,5,0.1,1.0,5,310,50.05,1.0,For all cases:fcmn=0.01,fcmx=0.99,Porosity=20%,adrg=1.810,3,bdrg=0.0,目录,过滤网几何导入,物理模型选择（,Physics,）,过滤网参数设定,过滤网材料选择,结果输出,1.,操作：,过滤网几何导入,导入过滤网图,类型,设定,单位转换,类型,选择,指定过滤网的孔隙率,Unit,单位,FLOW-3D,采用,单位为,SI,（,m,Kg,）,CGS,（,cm,g,）,ENGINEERING,（英制）,由于,大部分铸件绘图单位为,mm,，因此在,FLOW-3D,导入几何,时建议将单位转换至,CGS,制。,1 mm=0.1 cm,，因此单位转换时,Global magnitude,必须填入,0.1,。,2.,物理模型,指定类型,指定拖曳系数,3.,过滤网参数设定,指定参数,以,FAVOR,查看,网格建立,好坏,在网格,划分,完成,后,，可以用,FAVOR,查看,在现有网格数量设定下，是否能够完整的描述,几何外形,。,选择,Render,4,、,过滤网,材料选择,材料的材质会影响热传的速度以及温度的分布。不同的材料其温度传递的速度也会不同。,FLOW-3D,提供过滤网的材料，用户也可自己定义。,操作：选择,模具,材料,过滤网初始温度,/,热传系数,如果已知模具温度，直接填入温度。,FLOW-3D,采用,温度单位为,K,，因此必须把摄氏度,+273.15,。,指定热传系数,指定初始温度,结果,流体经过过滤网的状态,此课件下载可自行编辑修改，仅供参考！感谢您的支持，我们努力做得更好！谢谢,