fluent多孔介质模型
fluent多孔介质非平衡热模型
fluent多孔介质非平衡热模型
Fluent多孔介质非平衡热模型是针对多孔介质内部非平衡热传导现象而开发的一种数值模型，常用于研究岩石、煤矿、土壤等多孔介质内部的温度分布和热传输特性。
下面我们分步骤来详述这种模型的原理和应用。
一、多孔介质的物理现象
多孔介质是指由固相和空气、水等流体组成的介质，其物理性质和热传导特性与普通固体有所不同。
在多孔介质内，流体和固相之间的热传导存在着非平衡现象，即流体和固相的温度不相等。
二、Fluent多孔介质非平衡热模型的原理
Fluent多孔介质非平衡热模型通过建立多孔介质中流体和固相之间的能量差，来模拟多孔介质内部的非平衡热传导现象。
具体来说，该模型将多孔介质看作一个由不同孔隙大小和形状的小孔隙组成的连续介质，在计算时考虑每个小孔隙内的流体和固相的温度分布和热传输情况。
在Fluent多孔介质非平衡热模型中，流体和固相之间的能量传递被分解为两个部分：对流传热和固相-流体传热。
其中，对流传热主要是指流体在小孔隙内通过对流传播热量的过程，而固相-流体传热则是指流体与固相之间通过传导传热的过程。
三、Fluent多孔介质非平衡热模型的应用
Fluent多孔介质非平衡热模型在多孔介质热传输领域具有广泛应用。
如在岩石、土壤中的热传输现象研究中，该模型可用于模拟地下水热交换、地热能利用等方面的问题。
此外，该模型在生物医学领域中的应用也逐渐增多，如可用于模拟组织和器官内部的热代谢过程，进而帮助医学研究者预测疾病的发展趋势。
综上所述，Fluent多孔介质非平衡热模型是一种有效描述多孔介质内部非平衡热传导现象的数值模型，其应用对地下热交换、组织生物学等领域具有深远的意义。
fluent多孔介质资料搜集
1、多孔介质数值模拟
用fluent计算，多孔介质的数值模拟是怎么设置的？最好详细点，谢谢！
多孔介质模型比较复杂，建议用多孔阶跃模型，后者是前者的二维简化，设置简单，比前者更易用，计算也容易收敛。
只需要设置如下三个参数：
1、face pemeability（面渗透性）
2、Porous Medium Thickness(多孔介质的厚度）
3、Pressure-Jump Coecient（压力阶跃系数）
这三个参数，1、3可以根据压降与速度的函数关系式直接计算得出，比较简单，这里无法弄出公式，就不打了。
2、求教fluent中多孔介质使用的公式应该如何确定？
多孔介质里fluent做了大量简化主要设置孔隙率粘性系数和阻力系数孔隙率由材料提供商直接提供粘性系数和阻力系数可通过压力降与速度降的几组实验得出这在fluent 帮助文件里有说如果不用很精确或没有实验条件可由达西定律近似得出。
追问我看一些例子里有人说要运用udf自定义函数来确定公式，那请问是处理多孔介质问题是都需要运用udf自定义公式？
回答是的如果要精确模拟多孔介质内的情况一定要UDF 。
因为FLUENT中自带的设置模型过于简单所以如果你想得到精确解就一定要UDF 目前很多课题组专门做FLUENT 多孔介质编程方面的研究非常复杂如果你跟本人一样多孔介质只是模拟的一小部分建议还是简化处理不然会相当麻烦。
fluent中多孔介质模型的设置
fluent中多孔介质模型的设置7.19.6 User Inputs for Porous MediaWhen you are modeling a porous region, the only additional inputs for the problem setup are as follows. Optional inputs are indicated as such.1. Define the porous zone.2. Define the porous velocity formulation. (optional)3. Identify the fluid material flowing through the porous medium.4. Enable reactions for the porous zone, if appropriate, and select the reaction mechanism.5. Enable the Relative Velocity Resistance Formulation. By default, this option is already enabled and takes the moving porous media into consideration (as described in Section 7.19.6).6. Set the viscous resistance coefficients ( in Equation7.19-1,or in Equation 7.19-2) and the inertial resistance coefficients ( in Equation 7.19-1, or in Equation 7.19-2), and define the direction vectors for which they apply. Alternatively, specify the coefficients for the power-law model.7. Specify the porosity of the porous medium.8. Select the material contained in the porous medium (required only for models that include heat transfer). Note that the specific heat capacity, , for the selected material in the porous zone can only be entered as a constant value.9. Set the volumetric heat generation rate in the solid portion of the porous medium (or any other sources, such as mass or momentum). (optional) 10. Set any fixed values for solution variables in the fluid region (optional).11. Suppress the turbulent viscosity in the porous region, if appropriate.12. Specify the rotation axis and/or zone motion, if relevant.Methods for determining the resistance coefficients and/or permeability are presented below. If you choose to use the power-law approximation of the porous-media momentum source term, you will enter thecoefficients and in Equation 7.19-3 instead of the resistance coefficients and flow direction.You will set all parameters for the porous medium inthe Fluid panel (Figure 7.19.1), which is opened from the Boundary Conditions panel (as described in Section 7.1.4).Figure 7.19.1: The Fluid Panel for a Porous Zone Defining the Porous ZoneAs mentioned in Section 7.1, a porous zone is modeled as a special type of fluid zone. To indicate that the fluid zone is a porous region, enablethe Porous Zone option in the Fluid panel. The panel will expand to show the porous media inputs (as shown in Figure7.19.1).Defining the Porous Velocity FormulationThe Solver panel contains a Porous Formulation region where you can instruct FLUENT to use either a superficial or physical velocity in the porous medium simulation. By default, the velocity is set to SuperficialVelocity. For details about using the Physical Velocity formulation, see Section 7.19.7.Defining the Fluid Passing Through the Porous MediumTo define the fluid that passes through the porous medium, select the appropriate fluid in the Material Name drop-down list in the Fluid panel. If you want to check or modify the properties of the selected material, you can click Edit... to open the Material panel; this panel contains just the properties of the selected material, not the full contents of thestandard Materials panel.If you are modeling species transport or multiphase flow,the Material Name list will not appear in the Fluid panel. Forspecies calculations, the mixture material for all fluid/porous zones will be the material you specified in the SpeciesModel panel. For multiphase flows, the materials are specified when you define the phases, as described in Section 23.10.3. Enabling Reactions in a Porous ZoneIf you are modeling species transport with reactions, you can enable reactions in a porous zone by turning on the Reaction option inthe Fluid panel and selecting a mechanism in the ReactionMechanism drop-down list.If your mechanism contains wall surface reactions, you will also need to specify a value for the Surface-to-Volume Ratio. Thisvalue is the surface area of the pore walls per unit volume ( ), and can be thought of as a measure of catalyst loading. With this value, FLUENT can calculate the total surface area on which the reaction takes place in each cell bymultiplying by the volume of the cell. See Section 14.1.4 for detailsabout defining reaction mechanisms. See Section 14.2for details about wall surface reactions.Including the Relative Velocity Resistance FormulationPrior to FLUENT 6.3, cases with moving reference frames used the absolute velocities in the source calculations for inertial and viscous resistance. This approach has been enhanced so that relative velocities are used for the porous source calculations (Section 7.19.2). Using the Relative Velocity Resistance Formulation option (turned on by default) allows you to better predict the source terms for cases involving moving meshes or moving reference frames (MRF). This option works well in cases withnon-moving and moving porous media. Note that FLUENT will use the appropriate velocities (relative or absolute), depending on your case setup. Defining the Viscous and Inertial Resistance CoefficientsThe viscous and inertial resistance coefficients are both defined in the same manner. The basic approach for defining the coefficients using a Cartesian coordinate system is to define one direction vector in 2D or two direction vectors in 3D, and then specify the viscous and/or inertial resistance coefficients in each direction. In 2D, the second direction, which is not explicitly defined, is normal to the plane defined by the specified direction vector and the direction vector. In 3D, the third direction is normal to the plane defined by the two specified direction vectors. For a 3D problem, the second direction must be normal to the first. If you fail to specify two normal directions, the solver will ensure that they are normal by ignoring any component of the second direction that is in the first direction. You should therefore be certain that the first direction is correctly specified. You can also define the viscous and/or inertial resistance coefficients in each direction using a user-defined function (UDF). The user-defined options become available in the corresponding drop-down list when the UDF has been created and loaded into FLUENT. Note that the coefficients defined in the UDF must utilize the DEFINE_PROFILE macro. For moreinformation on creating and using user-defined function, see the separate UDF Manual.If you are modeling axisymmetric swirling flows, you can specify an additional direction component for the viscous and/or inertial resistance coefficients. This direction component is always tangential to the other two specified directions. This option is available for both density-based and pressure-based solvers.In 3D, it is also possible to define the coefficients using a conical (or cylindrical) coordinate system, as described below.Note that the viscous and inertial resistance coefficients aregenerally based on the superficial velocity of the fluid in the porous media.The procedure for defining resistance coefficients is as follows:1. Define the direction vectors.To use a Cartesian coordinate system, simply specify the Direction-1 Vector and, for 3D, the Direction-2 Vector. The unspecifieddirection will be determined as described above. These directionvectors correspond to the principle axes of the porous media.For some problems in which the principal axes of the porous mediumare not aligned with the coordinate axes of the domain, you may notknow a priori the direction vectors of the porous medium. In suchcases, the plane tool in 3D (or the line tool in 2D) can help you todetermine these direction vectors.(a) "Snap'' the plane tool (or the line tool) onto the boundary of theporous region. (Follow the instructions inSection 27.6.1 or 27.5.1 for initializing the tool to a position on anexisting surface.)(b) Rotate the axes of the tool appropriately until they are alignedwith the porous medium.(c) Once the axes are aligned, click on the Update From PlaneTool or Update From Line Tool button inthe Fluid panel. FLUENT will automatically set the Direction-1Vector to the direction of the red arrow of the tool, and (in 3D)the Direction-2 Vector to the direction of the green arrow.To use a conical coordinate system (e.g., for an annular, conical filter element), follow the steps below. This option is available only in 3D cases.(a) Turn on the Conical option.(b) Specify the Cone Axis Vector and Point on Cone Axis. Thecone axis is specified as being in the direction of the Cone AxisVector (unit vector), and passing through the Point on Cone Axis.The cone axis may or may not pass through the origin of thecoordinate system.(c) Set the Cone Half Angle (the angle between the cone's axis andits surface, shown in Figure 7.19.2). To use a cylindrical coordinate system, set the Cone Half Angle to 0.Figure 7.19.2: Cone Half AngleFor some problems in which the axis of the conical filter element is not aligned with the coordinate axes of the domain, you may notknow a priori the direction vector of the cone axis and coordinates ofa point on the cone axis. In such cases, the plane tool can help you todetermine the cone axis vector and point coordinates. One method is as follows:(a) Select a boundary zone of the conical filter element that isnormal to the cone axis vector in the drop-down list next to the Snap to Zone button.(b) Click on the Snap to Zone button. FLUENT will automatically"snap'' the plane tool onto the boundary. It will also set the Cone Axis Vector and the Point on Cone Axis. (Note that you will still have to set the Cone Half Angle yourself.)An alternate method is as follows:(a) "Snap'' the plane tool onto the boundary of the porous region.(Follow the instructions in Section 27.6.1 for initializing the tool to a position on an existing surface.)(b) Rotate and translate the axes of the tool appropriately until thered arrow of the tool is pointing in the direction of the cone axisvector and the origin of the tool is on the cone axis.(c) Once the axes and origin of the tool are aligned, click onthe Update From Plane Tool button inthe Fluid panel. FLUENT will automatically set the Cone AxisVector and the Point on Cone Axis. (Note that you will still have toset the Cone Half Angle yourself.)2. Under Viscous Resistance, specify the viscous resistancecoefficient in each direction.Under Inertial Resistance, specify the inertial resistance coefficient in each direction. (You will need to scroll down with the scroll bar to view these inputs.)For porous media cases containing highly anisotropic inertial resistances, enable Alternative Formulation under Inertial Resistance.The Alternative Formulation option provides better stability to the calculation when your porous medium is anisotropic. The pressure loss through the medium depends on the magnitude of the velocity vector ofthe i th component in the medium. Using the formulation ofEquation 7.19-6 yields the expression below:(7.19-10) Whether or not you use the Alternative Formulation option depends on how well you can fit your experimentally determined pressure drop data to the FLUENT model. For example, if the flow through the medium is aligned with the grid in your FLUENT model, then it will not make a difference whether or not you use the formulation.For more infomation about simulations involving highly anisotropic porous media, see Section 7.19.8.Note that the alternative formulation is compatible only with the pressure-based solver.If you are using the Conical specification method, Direction-1 is the cone axis direction, Direction-2 is the normal to the cone surface (radial ( )direction for a cylinder), and Direction-3 is the circumferential ( ) direction.In 3D there are three possible categories of coefficients, and in 2D there are two:In the isotropic case, the resistance coefficients in all directions are the same (e.g., a sponge). For an isotropic case, you must explicitlyset the resistance coefficients in each direction to the same value.When (in 3D) the coefficients in two directions are the same and those in the third direction are different or (in 2D) the coefficients inthe two directions are different, you must be careful to specify thecoefficients properly for each direction. For example, if you had aporous region consisting of cylindrical straws with small holes inthem positioned parallel to the flow direction, the flow would passeasily through the straws, but the flow in the other two directions(through the small holes) would be very little. If you had a plane offlat plates perpendicular to the flow direction, the flow would notpass through them at all; it would instead move in the other twodirections.In 3D the third possible case is one in which all three coefficients are different. For example, if the porous region consisted of a plane ofirregularly-spaced objects (e.g., pins), the movement of flow between the blockages would be different in each direction. You wouldtherefore need to specify different coefficients in each direction. Methods for deriving viscous and inertial loss coefficients are described in the sections that follow.Deriving Porous Media Inputs Based on Superficial Velocity, Using a Known Pressure LossWhen you use the porous media model, you must keep in mind that the porous cells in FLUENT are 100% open, and that the values that you specify for and/or must be based on this assumption. Suppose, however, that you know how the pressure drop varies with the velocity through the actual device, which is only partially open to flow. The following exercise is designed to show you how to compute a valuefor which is appropriate for the FLUENT model.Consider a perforated plate which has 25% area open to flow. The pressure drop through the plate is known to be 0.5 times the dynamic head in the plate. The loss factor, , defined as(7.19-11)is therefore 0.5, based on the actual fluid velocity in the plate, i.e., the velocity through the 25% open area. To compute an appropriate valuefor , note that in the FLUENT model:1. The velocity through the perforated plate assumes that the plate is 100% open.2. The loss coefficient must be converted into dynamic head loss per unit length of the porous region.Noting item 1, the first step is to compute an adjusted loss factor, , which would be based on the velocity of a 100% open area:(7.19-12) or, noting that for the same flow rate, ,(7.19-13)The adjusted loss factor has a value of 8. Noting item 2, you must now convert this into a loss coefficient per unit thickness of the perforated plate. Assume that the plate has a thickness of 1.0 mm (10 m). The inertial loss factor would then be(7.19-14)Note that, for anisotropic media, this information must be computed for each of the 2 (or 3) coordinate directions.Using the Ergun Equation to Derive Porous Media Inputs for a Packed BedAs a second example, consider the modeling of a packed bed. In turbulent flows, packed beds are modeled using both a permeability and an inertial loss coefficient. One technique for deriving the appropriate constants involves the use of the Ergun equation [ 98], a semi-empirical correlation applicable over a wide range of Reynolds numbers and for many types of packing:(7.19-15)When modeling laminar flow through a packed bed, the second term in the above equation may be dropped, resulting in the Blake-Kozenyequation [ 98]:(7.19-16) In these equations, is the viscosity, is the mean particlediameter, is the bed depth, and is the void fraction, defined as the volume of voids divided by the volume of the packed bed region. Comparing Equations 7.19-4 and 7.19-6 with 7.19-15, the permeability and inertial loss coefficient in each component direction may be identified as(7.19-17) and(7.19-18) Using an Empirical Equation to Derive Porous Media Inputs for Turbulent Flow Through a Perforated PlateAs a third example we will take the equation of Van Winkle et al. [ 279, 339] and show how porous media inputs can be calculated for pressure loss through a perforated plate with square-edged holes.The expression, which is claimed by the authors to apply for turbulent flow through square-edged holes on an equilateral triangular spacing, is(7.19-19) where= mass flow rate through the plate= the free area or total area of the holes= the area of the plate (solid and holes)= a coefficient that has been tabulated for various Reynolds-numberrangesand for various= the ratio of hole diameter to plate thicknessfor and for the coefficient takes a value of approximately 0.98, where the Reynolds number is based on hole diameter and velocity in the holes.Rearranging Equation 7.19-19, making use of the relationship(7.19-20)and dividing by the plate thickness, , we obtain(7.19-21)where is the superficial velocity (not the velocity in the holes). Comparing with Equation 7.19-6 it is seen that, for the direction normal to the plate, the constant can be calculated from(7.19-22)Using Tabulated Data to Derive Porous Media Inputs for Laminar Flow Through a Fibrous MatConsider the problem of laminar flow through a mat or filter pad which is made up of randomly-oriented fibers of glass wool. As an alternative to the Blake-Kozeny equation (Equation 7.19-16) we might choose to employ tabulated experimental data. Such data is available for many types offiber [ 158].fraction of dimensionless permeability of glass woolwhere and is the fiber diameter. , for use inEquation 7.19-4, is easily computed for a given fiber diameter and volume fraction.Deriving the Porous Coefficients Based on Experimental Pressure and Velocity DataExperimental data that is available in the form of pressure drop against velocity through the porous component, can be extrapolated to determine the coefficients for the porous media. To effect a pressure drop across a porous medium of thickness, , the coefficients of the porous media are determined in the manner described below.If the experimental data is:then an curve can be plotted to create a trendline through these points yielding the following equationwhere is the pressure drop and is the velocity.Note that a simplified version of the momentum equation, relating the pressure drop to the source term, can be expressed as (7.19-24)or(7.19-25)Hence, comparing Equation 7.19-23 to Equation 7.19-2, yields the following curve coefficients:(7.19-26)with kg/m , and a porous media thickness, , assumed to be 1m in this example, the inertial resistance factor, .Likewise,with , the viscous inertial resistancefactor,. Note that this same technique can be applied to the porous jump boundary condition. Similar to the case of the porous media, you have to take into account the thickness of the medium . Yourexperimental data can be plotted in ancurve, yielding an equation that is equivalent to Equation 7.22-1. From there, you can determine the permeability and the pressure jumpcoefficient .Using the Power-Law ModelIf you choose to use the power-law approximation of the porous-media momentum source term (Equation 7.19-3), the only inputs required are the coefficients and . Under Power Law Model in the Fluid panel, enter the values for C0 and C1. Note that the power-law model can be used in conjunction with the Darcy and inertia models.C0 must be in SI units, consistent with the value of C1.Defining PorosityTo define the porosity, scroll down below the resistance inputs inthe Fluid panel, and set the Porosity under Fluid Porosity .You can also define the porosity using a user-defined function (UDF). The user-defined option becomes available in the corresponding drop-down list when the UDF has been created and loaded into FLUENT. Note that the porosity defined in the UDF must utilize the DEFINE_PROFILE macro. For more information on creating and using user-defined function, see the separate UDF Manual.The porosity, , is the volume fraction of fluid within the porous region (i.e., the open volume fraction of the medium). The porosity is used in the prediction of heat transfer in the medium, as described in Section 7.19.3, and in the time-derivative term in the scalar transport equations for unsteady flow, as described in Section 7.19.5. It also impacts the calculation of reaction source terms and body forces in the medium. These sources will be proportional to the fluid volume in the medium. If you want to represent the medium as completely open (no effect of the solid medium), you should set the porosity equal to 1.0 (the default). When the porosity is equal to 1.0, the solid portion of the medium will have no impact on heat transfer or thermal/reaction source terms in the medium.Defining the Porous MaterialIf you choose to model heat transfer in the porous medium, you must specify the material contained in the porous medium.To define the material contained in the porous medium, scroll down below the resistance inputs in the Fluid panel, and select the appropriate solid in the Solid Material Name drop-down list under Fluid Porosity. If you want to check or modify the properties of the selected material, you canclick Edit... to open the Material panel; this panel contains just the properties of the selected material, not the full contents of thestandard Materials panel. In the Material panel, you can define thenon-isotropic thermal conductivity of the porous material using auser-defined function (UDF). The user-defined option becomes available in the corresponding drop-down list when the UDF has been created and loaded into FLUENT. Note that the non-isotropic thermal conductivity defined in the UDF must utilize the DEFINE_PROPERTY macro. For more information on creating and using user-defined function, see the separate UDF Manual.Defining SourcesIf you want to include effects of the heat generated by the porous medium in the energy equation, enable the Source Terms option and set anon-zero Energy source. The solver will compute the heat generated by the porous region by multiplying this value by the total volume of the cells comprising the porous zone. You may also define sources of mass, momentum, turbulence, species, or other scalar quantities, as described in Section 7.28.Defining Fixed ValuesIf you want to fix the value of one or more variables in the fluid region of the zone, rather than computing them during the calculation, you can do so by enabling the Fixed Values option. See Section 7.27 for details. Suppressing the Turbulent Viscosity in the Porous RegionAs discussed in Section 7.19.4, turbulence will be computed in the porous region just as in the bulk fluid flow. If you are using one of the turbulence models (with the exception of the Large Eddy Simulation (LES) Model), and you want the turbulence generation to be zero in the porous zone, turn on the Laminar Zone option in the Fluid panel. Refer to Section 7.17.1 for more information about suppressing turbulence generation.Specifying the Rotation Axis and Defining Zone MotionInputs for the rotation axis and zone motion are the same as for a standard fluid zone. See Section 7.17.1 for details.。
【2019年整理】多孔介质-Fluent模拟
7.19多孔介质边界条件多孔介质模型适用的范围非常广泛，包括填充床，过滤纸，多孔板，流量分配器，还有管群，管束系统。
当使用这个模型的时候，多孔介质将运用于网格区域，流场中的压降将由输入的条件有关，见Section 7.19.2.同样也可以计算热传导，基于介质和流场热量守恒的假设，见Section 7.19.3.通过一个薄膜后的已知速度/压力降低特性可以简化为一维多孔介质模型，简称为“多孔跳跃”。
多孔跳跃模型被运用于一个面区域而不是网格区域，而且也可以代替完全多孔介质模型在任何可能的时候，因为它更加稳定而且能够很好地收敛。
见Section 7.22.7.19.1 多孔介质模型的限制和假设多孔介质模型就是在定义为多孔介质的区域结合了一个根据经验假设为主的流动阻力。
本质上，多孔介质模型仅仅是在动量方程上叠加了一个动量源项。
这种情况下，以下模型方面的假设和限制就可以很容易得到：•因为没有表示多孔介质区域的实际存在的体，所以fluent默认是计算基于连续性方程的虚假速度。
做为一个做精确的选项，你可以适用fluent中的真是速度，见section7.19.7。
•多孔介质对湍流流场的影响，是近似的，见7.19.4。
•当在移动坐标系中使用多孔介质模型的时候，fluent既有相对坐标系也可以使用绝对坐标系，当激活相对速度阻力方程。
这将得到更精确的源项。
相关信息见section7.19.5和7.19.6。
•当需要定义比热容的时候，必须是常数。
7.19.2 多孔介质模型动量方程多孔介质模型的动量方程是在标准动量方程的后面加上动量方程源项。
源项包含两个部分：粘性损失项（达西公式项，方程7.19-1右边第一项），和惯性损失项（方程7.19-1右边第二项）(7.19-1)式中，si是i（x，y，z）动量方程的源项，是速度大小，D和C是矩阵。
动量源项对多孔介质区域的压力梯度有影响，生成一个与速度大小（速度平方）成正比的压降。
FLUENT多孔介质数值模拟设置
FLUENT多孔介质数值模拟设置C=对于不同D/t的不同雷诺数范围被列成不同的表的系数A_p=圆盘的面积（固体和洞)如果你选择在多孔介质中模拟热传导，你必须指定多孔介质中的材料以及多孔性。
要定义多孔介质的材料，向下拉流体面板中阻力输入底下的滚动条，然后在多孔热传导的固体材料下拉列表中选中适当的固体。
另一个处理收敛性差的要领是临时取消多孔介质模型（在流体面板中关闭多孔区域）然后获取一个不受多孔区域影响的初始流场。
取消多孔区域后，FLUE ＮT会将多孔区域处理为流体区域并按响应的流体区域来计算。
一旦获取了初始解，或者计算很容易收敛，你就可以激活多孔模型继续计算包罗多孔区域的流场（对于大阻力多孔介质不保举使用该要领）。
这些变量会在后处理面板的变量选择下拉菜谱制定类别中出现。
然后在多孔热传导下设定多孔性。
多孔性f是多孔介质中流体的体积分数（即介质的开放体积分数）。
多孔性用于介质中的热传导预测，处理要领请参阅多孔介质能量方程的处理一节。
它还对介质中的反应源项和体力的计算有影响。
这个源项和介质中流体的体积成比例。
如果你想要模拟完全开放的介质（固体介质没有影响），你应该设定多孔性为1.0。
当多孔性为1.0时，介质的固体部门对于热传导和（或）热源项/反应源项没有影响。
注意：多孔性永远不会影响介质中的流体速率，这已经在多孔介质的动量方程一节中介绍了。
不管你将多孔性设定为何值，，FLUEＮT所预测的速率都是介质中的外貌速率。
对于多孔介质动量源项（多孔介质动量方程中的方程5），如果你使用幂律模型近似，你只要在流体面板的幂律模型中输入系数C_0和C_1就可以了。
如果C_0或C_1为非零值，解算器会忽略面板中除了多孔介质幂律模型之外的所有输入。
定义源项一般说来，在模拟多孔介质时，你可以使用标准的解算步骤以及解参数的设置。
然而你会发现如果多孔区域在流动方向上压降至关大（比如：渗透性a很低或者内部因数C_2很大）的话，解的收敛速率就会变慢。
Fluent计算多孔介质模型资料
广东省深圳市宝安区沙井辛养社区西部工业园 TEL:+86-755-3366-8888 FAX:+86-755-3366-0612Fluent计算多孔介质模型资料这是一个多孔介质例子，进口速度为0.01m/s,组份为液态水和氧气，其中氧气从多孔介质porous jump 渗透过去，如何看氧气在tissue中扩散的。
porous jump的face permeability1 a=e-8 m_2thickness 设为0.0001pressure jump coefficient为默认porous zone设置如下：direction vector 1, 1,viscous resistance 100 eachinertial resistance 100 eachporosity 0.1边界条件设置如下：Ab – wall - defaultBc – wall – defaultBe – porous jump – face permeability 1e-8, porous medium thickness0.0001Cd – outflow rating – 0.5De – wall – defaultDefault interior – interiorDefault interior001 – interiorDefault interior019 – interiorEf – wall - defaultFg – outflow rating – 1Fluid - porous zone - direction vector 1, 1, viscous resistance 100 each,inertial resistance 100 each, porosity 0.1Gh- wall - defaultHi – wall - defaultHk - porous jump same conditions as otherIj – outflow – 0.5Jk – wall – defaultKl – wall – defaultLa – velocity inlet – 0.01 m/s, temperature 300K, 0.5 mass fraction O2 Lfluid – porous zone - direction vector 1, 1, viscous resistance 100 each,inertial resistance 100 each, porosity 0.1Pipefluid – fluid – default (no porous zone)Models – species transport – water and oxygen mixtureVariations – different boundary conditions at top and bottom (outflow, wall ect)注意,其中porous zone在gambit中设置为fluid，在fluent中设置为porous zone边界条件设置如下：Ab – wall - defaultBc – wall – defaultBe – porous jump – face permeability 1e-8, porous medium thickness0.0001Cd – outflow rating – 0.5De – wall – defaultDefault interior – interiorDefault interior001 – interiorDefault interior019 – interiorEf – wall - defaultFg – outflow rating – 1Fluid - porous zone - direction vector 1, 1, viscous resistance 100 each,inertial resistance 100 each, porosity 0.1Gh- wall - defaultHi – wall - defaultHk - porous jump same conditions as otherIj – outflow – 0.5Jk – wall – defaultKl – wall – defaultLa – velocity inlet – 0.01 m/s, temperature 300K, 0.5 mass fraction O2 Lfluid – porous zone - direction vector 1, 1, viscous resistance 100 each,inertial resistance 100 each, porosity 0.1Pipefluid – fluid – default (no porous zone)Models – species transport – water and oxygen mixtureVariations – different boundary conditions at top and bottom (outflow, wall ect) 注意,其中porous zone在gambit中设置为fluid，在fluent中设置为porous zone。
FLUENT多孔介质条件
多孔介质的动量方程
多孔介质的动量方程具有附加的动量源项。 源项由两部分组成， 一部分是粘性损失项(Darcy)， 另一个是内部损失项：
其中 S_i 是 i 向(x, y, or z)动量源项，D 和 C 是规定的矩阵。在多孔介质单元中，动量损 失对于压力梯度有贡献，压降和流体速度（或速度方阵）成比例。 对于简单的均匀多孔介质：
Figure 1:多孔区域的流体面板
定义多孔区域
正如定义边界条件概述中所提到的，多孔区域是作为特定类型的流体区域来模 拟的。亚表明流体区域是多孔区域，请在流体面板中激活多孔区域选项。面板会自动扩展到 多孔介质输入状态。
定义穿越多孔介质的流体
在材料名字下拉菜单中选择适当的流体就可以定义通过多孔介质的流体了。如 果你模拟组分输运或者多相流， 流体面板中就不会出现材料名字下拉菜单了。 对于组分计算 ， 所有流体和/或多孔区域的混合材料就是你在组分模型面板中指定的材料。 对于多相流模型， 所有流体和/或多孔区域的混合材料就是你在多相流模型面板中指定的材料。
6. 7.
如果合适的话，限制多孔区域的湍流粘性。 如果相关的话，指定旋转轴和/或区域运动。
在定义粘性和内部阻力系数中描述了决定阻力系数和/或渗透性的方法。如果你使用多孔动 量源项的幂律近似，你需要输入多孔介质动量方程5中的 C_0和 C_1来取代阻力系数和流动 方向。 在流体面板中（下图）你需要设定多孔介质的所有参数，该面板是从边界条件菜单中打开的 （详细内容请参阅边界条件的设定一节）
在多孔介质区域三个坐标方向的压降为：
其中为多孔介质动量方程1中矩阵 D 的元素 vj 为三个方向上的分速度，D n_x、D n_y、以及 D n_z 为三个方向上的介质厚度。 在这里介质厚度其实就是模型区域内的多孔区域的厚度。 因此如果模型的厚度和实际厚 度不同，你必须调节1/a_ij 的输入。.
FLUENT多孔介质数值模拟设置
FLUENT多孔介质数值模拟设置多孔介质条件多孔介质模型可以应用于很多问题，如通过充满介质的流动、通过过滤纸、穿孔圆盘、流量分配器以及管道堆的流动。
当你使用这一模型时，你就定义了一个具有多孔介质的单元区域，而且流动的压力损失由多孔介质的动量方程中所输入的内容来决定。
通过介质的热传导问题也可以得到描述，它服从介质和流体流动之间的热平衡假设，具体内容可以参考多孔介质中能量方程的处理一节。
多孔介质的一维化简模型，被称为多孔跳跃，可用于模拟具有已知速度/压降特征的薄膜。
多孔跳跃模型应用于表面区域而不是单元区域，并且在尽可能的情况下被使用（而不是完全的多孔介质模型），这是因为它具有更好的鲁棒性，并具有更好的收敛性。
详细内容请参阅多孔跳跃边界条件。
多孔介质模型的限制如下面各节所述，多孔介质模型结合模型区域所具有的阻力的经验公式被定义为“多孔”。
事实上多孔介质不过是在动量方程中具有了附加的动量损失而已。
因此，下面模型的限制就可以很容易的理解了。
流体通过介质时不会加速，因为事实上出现的体积的阻塞并没有在模型中出现。
这对于过渡流是有很大的影响的，因为它意味着FLUENT不会正确的描述通过介质的过渡时间。
多孔介质对于湍流的影响只是近似的。
详细内容可以参阅湍流多孔介质的处理一节。
多孔介质的动量方程多孔介质的动量方程具有附加的动量源项。
源项由两部分组成，一部分是粘性损失项 (Darcy)，另一个是内部损失项：其中S_i是i向(x, y, or z)动量源项，D和C是规定的矩阵。
在多孔介质单元中，动量损失对于压力梯度有贡献，压降和流体速度（或速度方阵）成比例。
对于简单的均匀多孔介质：其中a是渗透性，C_2时内部阻力因子，简单的指定D和C分别为对角阵1/a 和C_2其它项为零。
FLUENT还允许模拟的源项为速度的幂率：其中C_0和C_1为自定义经验系数。
注意：在幂律模型中，压降是各向同性的，C_0的单位为国际标准单位。
多孔介质的Darcy定律通过多孔介质的层流流动中，压降和速度成比例，常数C_2可以考虑为零。
fluent多孔介质模型
div u div grad S t
运动方程：
Dv Fb p f Dt
惯性力 品质力 表面力
多孔介质模拟方法是将流动区域中固体结构的 作用看作是附加在流体上的分布阻力。
4
多孔介质的源项
多孔介质的作用是在动量方程中增加一个源项来模拟，源项由两 部分组成：一个粘性损失项和一个惯性损失项。
采用上表的数据可以拟合出一条“速度－压强降”曲线，其方程 为：
对比上述两式便可求出粘性阻力系数和惯性阻力系数。
13
实例计算
进 口
Porous one WALL symmetr y 出 口
Porous Porous three two
上图中的计算区域尺寸如下： 总的计算域：长1m，宽0.1m； Porous two：长0.57m，宽0.02m； （处于正中间） Porous one：宽0.03m，高0.06m； Porous three：宽0.03m，高0.06m； 边界条件如上图中所示，进口取velocity inlet，速 度为0.01m/s；出口取pressure outlet，压力值为大气压。 三个多孔介质区中，porous one和porous three的性质一 样。Porous two的粘性阻力系数为1e+10，其余多孔介质区 为1e+13.由于是低速层流流动，不考虑惯性阻力的影响。
△Py, △Pz分别是x,y,z三个方向的压力降。△nx, 别是多孔介质在x,y,z三个方向的真实厚度。
△Px,
△ny,△ Nhomakorabean z分
7
能量方程的处理
能量方程：
多孔介质对能量方程修正：
多孔介质-Fluent模拟
7.19多孔介质边界条件多孔介质模型适用的范围非常广泛，包括填充床，过滤纸，多孔板，流量分配器，还有管群，管束系统。
当使用这个模型的时候，多孔介质将运用于网格区域，流场中的压降将由输入的条件有关，见Section 7.19.2.同样也可以计算热传导，基于介质和流场热量守恒的假设，见Section 7.19.3.通过一个薄膜后的已知速度/压力降低特性可以简化为一维多孔介质模型，简称为“多孔跳跃”。
多孔跳跃模型被运用于一个面区域而不是网格区域，而且也可以代替完全多孔介质模型在任何可能的时候，因为它更加稳定而且能够很好地收敛。
见Section 7.22.7.19.1 多孔介质模型的限制和假设多孔介质模型就是在定义为多孔介质的区域结合了一个根据经验假设为主的流动阻力。
本质上，多孔介质模型仅仅是在动量方程上叠加了一个动量源项。
这种情况下，以下模型方面的假设和限制就可以很容易得到：•因为没有表示多孔介质区域的实际存在的体，所以fluent默认是计算基于连续性方程的虚假速度。
做为一个做精确的选项，你可以适用fluent中的真是速度，见section7.19.7。
•多孔介质对湍流流场的影响，是近似的，见7.19.4。
•当在移动坐标系中使用多孔介质模型的时候，fluent既有相对坐标系也可以使用绝对坐标系，当激活相对速度阻力方程。
这将得到更精确的源项。
相关信息见section7.19.5和7.19.6。
•当需要定义比热容的时候，必须是常数。
7.19.2 多孔介质模型动量方程多孔介质模型的动量方程是在标准动量方程的后面加上动量方程源项。
源项包含两个部分：粘性损失项（达西公式项，方程7.19-1右边第一项），和惯性损失项（方程7.19-1右边第二项）(7.19-1)式中，si是i（x，y，z）动量方程的源项，是速度大小，D和C是矩阵。
动量源项对多孔介质区域的压力梯度有影响，生成一个与速度大小（速度平方）成正比的压降。
fluent多孔跳跃模型参数设置
fluent多孔跳跃模型参数设置摘要：1.Fluent 软件简介2.多孔跳跃模型的设置方法3.多孔介质模型的参数设置4.模型应用实例正文：一、Fluent 软件简介Fluent 是一款国际上流行的商用计算流体动力学（CFD）软件包，广泛应用于航空航天、汽车设计、石油天然气和涡轮机设计等领域。
它具有丰富的物理模型、先进的数值方法和强大的前后处理功能，在美国的市场占有率达到60%。
二、多孔跳跃模型的设置方法在Fluent 中，多孔跳跃模型的设置主要分为以下几个步骤：1.定义多孔介质包含的材料属性和多孔性。
2.设定多孔区域的固体部分的体积热生成速度（或任何其它源项，如质量、动量）（此项可选）。
3.如果合适的话，限制多孔区域的湍流粘性。
4.如果相关的话，指定旋转轴和/或区域运动。
三、多孔介质模型的参数设置在Fluent 中设置多孔介质模型时，需要考虑以下几个参数：1.空隙率：多孔介质中的空隙体积与总体积之比。
2.热导率：多孔介质中的热传导性能，单位为瓦特/(米·开尔文)。
3.密度：多孔介质中的质量密度，单位为千克/立方米。
4.比热容：多孔介质中的比热容，单位为焦耳/(千克·开尔文)。
5.粘性阻力：多孔介质中的流体阻力，单位为帕斯卡。
6.内部阻力：多孔介质中的内部阻力，单位为帕斯卡。
四、模型应用实例Fluent 中的多孔跳跃模型在许多实际应用中都取得了良好的效果，例如在航空航天、汽车设计、石油天然气和涡轮机设计等领域。
通过设置合适的多孔介质模型参数，可以更准确地模拟流体在多孔介质中的流动过程，从而为工程设计提供有力的支持。
综上所述，Fluent 中的多孔跳跃模型参数设置涉及多个方面，需要综合考虑多孔介质的材料属性、热生成速度、湍流粘性等因素。
fluent多孔介质模型参数含义
fluent多孔介质模型参数含义
在Fluent中，多孔介质模型是用于模拟流体通过多孔介质媒体的传输过程的一
种方法。
多孔介质可以是任何具有孔隙结构的固体材料，如岩石、土壤等。
在多孔介质模型中，有几个关键参数需要理解和定义，以确保正确模拟流体在
多孔介质中的行为。
1. 多孔度（Porosity）：多孔度是指多孔介质中孔隙的体积占总体积的比例。
它是一个介于0和1之间的值，表示孔隙占据了多大的空间。
较高的多孔度意味着更多的孔隙空间可供流体流动。
2. 渗透率（Permeability）：渗透率是多孔介质中流体通过的能力。
它是描述多
孔介质对流体渗透性的度量。
渗透率与多孔度有关，但也受到孔隙间连通性和孔隙尺寸分布的影响。
较高的渗透率表示流体更容易通过多孔介质。
3. 波尔兹曼常数（Forchheimer's constant）：波尔兹曼常数用于描述多孔介质
中非线性渗透率的影响。
它是渗透率随速度变化的一种补偿，考虑了流体在多孔介质中的非线性行为。
4. 动力学黏度（Dynamic viscosity）：动力学黏度是流体内部的黏性阻力，影
响流体通过多孔介质时的阻力。
较大的动力学黏度表示流体在通过多孔介质时会遇到更大的阻力。
除了这些参数外，Fluent中的多孔介质模型还可以考虑压力损失、介质方向性、层流/湍流以及热传导等因素，以更准确地模拟多孔介质中的流体传输过程。
了解和正确定义这些参数非常重要，因为它们可以影响模拟结果的准确性和可
靠性。
根据不同的多孔介质特性和流体行为，选择适合的参数值是确保模拟结果合理和可靠的关键一步。
多孔介质模型
FLUENT6.1全攻略分量来定义。
图8-26 Solid（固体）面板6. 定义辐射参数如果使用DO模型计算辐射过程，可以在Participates in Radiation（是否参与辐射）选项中确定固体区域是否参与辐射过程。
8.19 多孔介质条件很多问题中包含多孔介质的计算，比如流场中包括过滤纸、分流器、多孔板和管道集阵等边界时就需要使用多孔介质条件。
在计算中可以定义某个区域或边界为多孔介质，并通过参数输入定义通过多孔介质后流体的压力降。
在热平衡假设下，也可以确定多孔介质的热交换过程。
在薄的多孔介质面上可以用一维假设“多孔跳跃（porous jump）”定义速度和压强的降落特征。
多孔跳跃模型用于面区域，而不是单元区域，在计算中应该尽量使用这个模型，因为这个模型可以增强计算的稳定性和收敛性。
9FLUENT6.1全攻略108.19.1 多孔介质模型的假设和限制条件多孔介质模型采用经验公式定义多孔介质上的流动阻力。
从本质上说，多孔介质模型就是在动量方程中增加了一个代表动量消耗的源项。
因此，多孔介质模型需要满足下面的限制条件：（1）因为多孔介质的体积在模型中没有体现，在缺省情况下，FLUENT 在多孔介质内部使用基于体积流量的名义速度来保证速度矢量在通过多孔介质时的连续性。
如果希望更精确地进行计算，也可以让FLUENT 在多孔介质内部使用真实速度，详情见8.19.7节。
（2）多孔介质对湍流的影响仅仅是近似。
（3）在移动坐标系中使用多孔介质模型时，应该使用相对坐标系，而不是绝对坐标系，以保证获得正确的源项解。
8.19.2 多孔介质的动量方程在动量方程中增加一个动量源项可以模拟多孔介质的作用。
源项由两部分组成：一个粘性损失项，即方程（8-45）右端第一项；和一个惯性损失项，即方程（8-45）右端第二项。
⎟⎟⎠⎞⎜⎜⎝⎛+−=∑∑==313121j j mag ij j j ij i v v C v D S ρμ （8-45）式中i S 是第i 个（x 、y 或z 方向）动量方程中的源项，D 和C 是给定矩阵。
fluent中多孔介质设置问题和算例
经过痛苦的一段经历，终于将局部问题真相大白，为了使保位不再经过我之痛苦，现在将本人多孔介质经验公布如下，希望各位能加精：1。
Gambit中划分网格之后，定义需要做为多孔介质的区域为fluid,与缺省的fluid分别开来，再定义其名称，我习惯将名称定义为porous;2。
在fluent中定义边界条件define-boundary condition-porous(刚定义的名称)，将其设置边界条件为fluid,点击set按钮即弹出与fluid边界条件一样的对话框，选中porous zone与laminar复选框,再点击porous zone标签即出现一个带有滚动条的界面；3。
porous zone设置方法：1）定义矢量：二维定义一个矢量，第二个矢量方向不用定义，是与第一个矢量方向正交的；三维定义二个矢量，第三个矢量方向不用定义，是与第一、二个矢量方向正交的；（如何知道矢量的方向：打开grid图，看看X,Y,Z的方向，如果是X向，矢量为1,0,0,同理Y向为0,1,0，Z向为0,0,1,如果所需要的方向与坐标轴正向相反，则定义矢量为负）圆锥坐标与球坐标请参考fluent帮助。
2）定义粘性阻力1/a与部阻力C2：请参看本人上一篇博文“终于搞清fluent中多孔粘性阻力与部阻力的计算方法”，此处不赘述；3）如果了定义粘性阻力1/a与部阻力C2,就不用定义C1与C0，因为这是两种不同的定义方法，C1与C0只在幂率模型中出现，该处保持默认就行了；4）定义孔隙率porousity，默认值1表示全开放，此值按实验测值填写即可。
完了，其他设置与普通k-e或RSM一样。
总结一下，与君共享!Tutorial 7. Modeling Flow Through PorousMediaIntroductionMany industrial applications involve the modeling of flow through porous media, suchas filters, catalyst beds, and packing. This tutorial illustrates how to set up and solve aproblem involving gas flow through porous media.The industrial problem solved here involves gas flow through a catalytic converter. Catalyticconverters are commonly used to purify emissions from gasoline and diesel enginesby converting environmentally hazardous exhaust emissions to acceptable substances.Examples of such emissions include carbon monoxide (CO), nitrogen oxides (NOx), andunburned hydrocarbon fuels. These exhaust gas emissions are forced through a substrate,which is a ceramic structure coated with a metal catalyst such as platinum or palladium.The nature of the exhaust gas flow is a very important factor in determining the performanceof the catalytic converter. Of particular importance is the pressure gradientand velocity distribution through the substrate. Hence CFD analysis is used to designefficient catalytic converters: by modeling the exhaust gas flow, the pressure drop andthe uniformity of flow through the substrate can be determined. In this tutorial, FLUENTis used to model the flow of nitrogen gas through a catalytic converter geometry, so thatthe flow field structure may be analyzed.This tutorial demonstrates how to do the following:_ Set up a porous zone for the substrate with appropriate resistances._ Calculate a solution for gas flow through the catalytic converter using the pressurebasedsolver._ Plot pressure and velocity distribution on specified planes of the geometry. _ Determine the pressure drop through the substrate and the degree ofnon-uniformityof flow through cross sections of the geometry using X-Y plots and numerical reports.Problem DescriptionThe catalytic converter modeled here is shown in Figure 7.1. The nitrogen flows inthrough the inlet with a uniform velocity of 22.6 m/s, passes through a ceramic monolithsubstrate with square shaped channels, and then exits through the outlet.While the flow in the inlet and outlet sections is turbulent, the flow through the substrateis laminar and is characterized by inertial and viscous loss coefficients in the flow (X)direction. The substrate is impermeable in other directions, which is modeled using losscoefficients whose values are three orders of magnitude higher than in the X direction.Setup and SolutionStep 1: Grid1. Read the mesh file (catalytic converter.msh).File /Read /Case...2. Check the grid.Grid /CheckFLUENT will perform various checks on the mesh and report the progress in theconsole. Make sure that the minimum volume reported is a positive number.3. Scale the grid.Grid!Scale...(a) Select mm from the Grid Was Created In drop-down list.(b) Click the Change Length Units button.All dimensions will now be shown in millimeters.(c) Click Scale and close the Scale Grid panel.4. Display the mesh.Display /Grid...(a) Make sure that inlet, outlet, substrate-wall, and wall are selected in the Surfacesselection list.(b) Click Display.(c) Rotate the view and zoom in to get the display shown in Figure 7.2.(d) Close the Grid Display panel.The hex mesh on the geometry contains a total of 34,580 cells.Step 2: Models1. Retain the default solver settings.Define /Models /Solver...2. Select the standard k-ε turbulence model.Define/ Models /Viscous...Step 3: Materials1. Add nitrogen to the list of fluid materials by copying it from the Fluent Databasefor materials.Define /Materials...(a) Click the Fluent Database... button to open the Fluent Database Materialspanel.i. Select nitrogen (n2) from the list of Fluent Fluid Materials.ii. Click Copy to copy the information for nitrogen to your list of fluid materials. iii. Close the Fluent Database Materials panel.(b) Close the Materials panel.Step 4: Boundary Conditions. Define /Boundary Conditions...1. Set the boundary conditions for the fluid (fluid).(a) Select nitrogen from the Material Name drop-down list.(b) Click OK to close the Fluid panel.2. Set the boundary conditions for the substrate (substrate).(a) Select nitrogen from the Material Name drop-down list.(b) Enable the Porous Zone option to activate the porous zone model.(c) Enable the Laminar Zone option to solve the flow in the porous zone withoutturbulence.(d) Click the Porous Zone tab.i. Make sure that the principal direction vectors are set as shown in e the scroll bar to access the fields that are not initially visible in thepanel.ii. Enter the values in Table 7.2 for the Viscous Resistance and Inertial Resistance.Scroll down to access the fields that are not initially visible in the panel.(e) Click OK to close the Fluid panel.3. Set the velocity and turbulence boundary conditions at the inlet (inlet).(a) Enter 22.6 m/s for the Velocity Magnitude.(b) Select Intensity and Hydraulic Diameter from the Specification Method dropdownlist in the Turbulence group box.(c) Retain the default value of 10% for the Turbulent Intensity.(d) Enter 42 mm for the Hydraulic Diameter.(e) Click OK to close the Velocity Inlet panel.4. Set the boundary conditions at the outlet (outlet).(a) Retain the default setting of 0 for Gauge Pressure.(b) Select Intensity and Hydraulic Diameter from the Specification Method dropdownlist in the Turbulence group box.(c) Enter 5% for the Backflow Turbulent Intensity.(d) Enter 42 mm for the Backflow Hydraulic Diameter.(e) Click OK to close the Pressure Outlet panel.5. Retain the default boundary conditions for the walls (substrate-wall and wall) andclose the Boundary Conditions panel.Step 5: Solution1. Set the solution parameters.Solve /Controls /Solution...(a) Retain the default settings for Under-Relaxation Factors.(b) Select Second Order Upwind from the Momentum drop-down list in the Discretizationgroup box.(c) Click OK to close the Solution Controls panel.2. Enable the plotting of residuals during the calculation.Solve/Monitors/Residual...(a) Enable Plot in the Options group box.(b) Click OK to close the Residual Monitors panel.3. Enable the plotting of the mass flow rate at the outlet.Solve / Monitors /Surface...(a) Set the Surface Monitors to 1.(b) Enable the Plot and Write options for monitor-1, and click the Define... buttonto open the Define Surface Monitor panel.i. Select Mass Flow Rate from the Report Type drop-down list.ii. Select outlet from the Surfaces selection list.iii. Click OK to close the Define Surface Monitors panel.(c) Click OK to close the Surface Monitors panel.4. Initialize the solution from the inlet.Solve /Initialize /Initialize...(a) Select inlet from the Compute From drop-down list.(b) Click Init and close the Solution Initialization panel.5. Save the case file (catalytic converter.cas).File /Write /Case...6. Run the calculation by requesting 100 iterations.Solve /Iterate...(a) Enter 100 for the Number of Iterations.(b) Click Iterate.The FLUENT calculation will converge in approximately 70 iterations. By thispoint the mass flow rate monitor has attended out, as seen in Figure 7.3.(c) Close the Iterate panel.7. Save the case and data files (catalytic converter.cas and catalytic converter.dat).File /Write /Case & Data...Note: If you choose a file name that already exists in the current folder, FLUENT will prompt you for confirmation to overwrite the file.Step 6: Post-processing1. Create a surface passing through the centerline for post-processing purposes. Surface/Iso-Surface...(a) Select Grid... and Y-Coordinate from the Surface of Constant drop-down lists.(b) Click Compute to calculate the Min and Max values.(c) Retain the default value of 0 for the Iso-Values.(d) Enter y=0 for the New Surface Name.(e) Click Create.2. Create cross-sectional surfaces at locations on either side of the substrate, as wellas at its center.Surface /Iso-Surface...(a) Select Grid... and X-Coordinate from the Surface of Constant drop-down lists.(b) Click Compute to calculate the Min and Max values.(c) Enter 95 for Iso-Values.(d) Enter x=95 for the New Surface Name.(e) Click Create.(f) In a similar manner, create surfaces named x=130 and x=165 with Iso-Valuesof 130 and 165, respectively. Close the Iso-Surface panel after all the surfaceshave been created.3. Create a line surface for the centerline of the porous media.Surface /Line/Rake...(a) Enter the coordinates of the line under End Points, using the starting coordinateof (95, 0, 0) and an ending coordinate of (165, 0, 0), as shown.(b) Enter porous-cl for the New Surface Name.(c) Click Create to create the surface.(d) Close the Line/Rake Surface panel.4. Display the two wall zones (substrate-wall and wall).Display /Grid...(a) Disable the Edges option.(b) Enable the Faces option.(c) Deselect inlet and outlet in the list under Surfaces, and make sure that onlysubstrate-wall and wall are selected.(d) Click Display and close the Grid Display panel.(e) Rotate the view and zoom so that the display is similar to Figure 7.2.5. Set the lighting for the display.Display /Options...(a) Enable the Lights On option in the Lighting Attributes group box.(b) Retain the default selection of Gourand in the Lighting drop-down list.(c) Click Apply and close the Display Options panel.6. Set the transparency parameter for the wall zones (substrate-wall and wall). Display/Scene...(a) Select substrate-wall and wall in the Names selection list.(b) Click the Display... button under Geometry Attributes to open the DisplayProperties panel.i. Set the Transparency slider to 70.ii. Click Apply and close the Display Properties panel.(c) Click Apply and then close the Scene Description panel.7. Display velocity vectors on the y=0 surface.Display /Vectors...(a) Enable the Draw Grid option.The Grid Display panel will open.i. Make sure that substrate-wall and wall are selected in the list under Surfaces. ii. Click Display and close the Display Grid panel.(b) Enter 5 for the Scale.(c) Set Skip to 1.(d) Select y=0 from the Surfaces selection list.(e) Click Display and close the Vectors panel.The flow pattern shows that the flow enters the catalytic converter as a jet, withrecirculation on either side of the jet. As it passes through the porous substrate, itdecelerates and straightens out, and exhibits a more uniform velocity distribution.This allows the metal catalyst present in the substrate to be more effective.Figure 7.4: Velocity Vectors on the y=0 Plane8. Display filled contours of static pressure on the y=0 plane.Display /Contours...(a) Enable the Filled option.(b) Enable the Draw Grid option to open the Display Grid panel.i. Make sure that substrate-wall and wall are selected in the list under Surfaces. ii. Click Display and close the Display Grid panel.(c) Make sure that Pressure... and Static Pressure are selected from the Contoursof drop-down lists.(d) Select y=0 from the Surfaces selection list.(e) Click Display and close the Contours panel.Figure 7.5: Contours of the Static Pressure on the y=0 planeThe pressure changes rapidly in the middle section, where the fluid velocity changesas it passes through the porous substrate. The pressure drop can be high, due to theinertial and viscous resistance of the porous media. Determining this pressure dropis a goal of CFD analysis. In the next step, you will learn how to plot the pressuredrop along the centerline of the substrate.9. Plot the static pressure across the line surface porous-cl.Plot /XY Plot...(a) Make sure that the Pressure... and Static Pressure are selected from the Y AxisFunction drop-down lists.(b) Select porous-cl from the Surfaces selection list.(c) Click Plot and close the Solution XY Plot panel.Figure 7.6: Plot of the Static Pressure on the porous-cl Line Surface In Figure 7.6, the pressure drop across the porous substrate can be seen to beroughly 300 Pa.10. Display filled contours of the velocity in the X direction on the x=95, x=130 andx=165 surfaces.Display /Contours...(a) Disable the Global Range option.(b) Select Velocity... and X Velocity from the Contours of drop-down lists.(c) Select x=130, x=165, and x=95 from the Surfaces selection list, and deselecty=0.(d) Click Display and close the Contours panel.The velocity profile becomes more uniform as the fluid passes through the porousmedia. The velocity is very high at the center (the area in red) just before thenitrogen enters the substrate and then decreases as it passes through and exits thesubstrate. The area in green, which corresponds to a moderate velocity, increasesin extent.Figure 7.7: Contours of the X Velocity on the x=95, x=130, and x=165 Surfaces 11. Use numerical reports to determine the average, minimum, and maximum of thevelocity distribution before and after the porous substrate.Report /Surface Integrals...(a) Select Mass-Weighted Average from the Report Type drop-down list.(b) Select Velocity and X Velocity from the Field Variable drop-down lists.(c) Select x=165 and x=95 from the Surfaces selection list.(d) Click Compute.(e) Select Facet Minimum from the Report Type drop-down list and click Computeagain.(f) Select Facet Maximum from the Report Type drop-down list and click Computeagain.(g) Close the Surface Integrals panel.The numerical report of average, maximum and minimum velocity can be seen inthe main FLUENT console, as shown in the following example:The spread between the average, maximum, and minimum values for X velocitygives the degree to which the velocity distribution is non-uniform. You can also usethese numbers to calculate the velocity ratio (i.e., the maximum velocity divided bythe mean velocity) and the space velocity (i.e., the product of the mean velocity andthe substrate length).Custom field functions and UDFs can be also used to calculate more complex measuresof non-uniformity, such as the standard deviation and the gamma uniformityindex. SummaryIn this tutorial, you learned how to set up and solve a problem involving gas flow throughporous media in FLUENT. You also learned how to perform appropriatepost-processingto investigate the flow field, determine the pressure drop across the porous media andnon-uniformity of the velocity distribution as the fluid goes through the porous media.Further ImprovementsThis tutorial guides you through the steps to reach an initial solution. You may be ableto obtain a more accurate solution by using an appropriate higher-order discretizationscheme and by adapting the grid. Grid adaption can also ensure that the solution isindependent of the grid. These steps are demonstrated in Tutorial1.。
多孔介质-Fluent模拟
多孔介质-Fluent模拟7.19多孔介质边界条件多孔介质模型适用的范围非常广泛，包括填充床，过滤纸，多孔板，流量分配器，还有管群，管束系统。
当使用这个模型的时候，多孔介质将运用于网格区域，流场中的压降将由输入的条件有关，见Section 7.19.2.同样也可以计算热传导，基于介质和流场热量守恒的假设，见Section 7.19.3.通过一个薄膜后的已知速度/压力降低特性可以简化为一维多孔介质模型，简称为“多孔跳跃”。
多孔跳跃模型被运用于一个面区域而不是网格区域，而且也可以代替完全多孔介质模型在任何可能的时候，因为它更加稳定而且能够很好地收敛。
见Section 7.22.7.19.1 多孔介质模型的限制和假设多孔介质模型就是在定义为多孔介质的区域结合了一个根据经验假设为主的流动阻力。
本质上，多孔介质模型仅仅是在动量方程上叠加了一个动量源项。
这种情况下，以下模型方面的假设和限制就可以很容易得到:, 因为没有表示多孔介质区域的实际存在的体，所以fluent默认是计算基于连续性方程的虚假速度。
做为一个做精确的选项，你可以适用fluent中的真是速度，见section7.19.7。
, 多孔介质对湍流流场的影响，是近似的，见7.19.4。
, 当在移动坐标系中使用多孔介质模型的时候，fluent既有相对坐标系也可以使用绝对坐标系，当激活相对速度阻力方程。
这将得到更精确的源项。
相关信息见section7.19.5和7.19.6。
, 当需要定义比热容的时候，必须是常数。
7.19.2 多孔介质模型动量方程多孔介质模型的动量方程是在标准动量方程的后面加上动量方程源项。
源项包含两个部分:粘性损失项(达西公式项，方程7.19-1右边第一项)，和惯性损失项(方程7.19-1右边第二项)(7.19-1)式中，si是i(x，y，z)动量方程的源项，是速度大小，D和C是矩阵。
动量源项对多孔介质区域的压力梯度有影响，生成一个与速度大小(速度平方)成正比的压降。
FLUENT多孔介质数值模拟设置
FLUEN■多孔介质数值模拟设置多孔介质条件多孔介质模型可以应用于很多问题，如通过充满介质的流动、通过过滤纸、穿孔圆盘、流量分配器以及管道堆的流动。
当你使用这一模型时，你就定义了一个具有多孔介质的单元区域，而且流动的压力损失由多孔介质的动量方程中所输入的内容来决定。
通过介质的热传导问题也可以得到描述，它服从介质和流体流动之间的热平衡假设，具体内容可以参考多孔介质中能量方程的处理一节。
多孔介质的一维化简模型，被称为多孔跳跃，可用于模拟具有已知速度/压降特征的薄膜。
多孔跳跃模型应用于表面区域而不是单元区域，并且在尽可能的情况下被使用(而不是完全的多孔介质模型)，这是因为它具有更好的鲁棒性，并具有更好的收敛性。
详细内容请参阅多孔跳跃边界条件。
多孔介质模型的限制如下面各节所述，多孔介质模型结合模型区域所具有的阻力的经验公式被定义为“多孔”。
事实上多孔介质不过是在动量方程中具有了附加的动量损失而已。
因此，下面模型的限制就可以很容易的理解了。
流体通过介质时不会加速，因为事实上出现的体积的阻塞并没有在模型中出现。
这对于过渡流是有很大的影响的，因为它意味着FLUENT不会正确的描述通过介质的过渡时间。
多孔介质对于湍流的影响只是近似的。
详细内容可以参阅湍流多孔介质的处理一节。
多孔介质的动量方程多孔介质的动量方程具有附加的动量源项。
源项由两部分组成，一部分是粘性损失项(Darcy)，另一个是内部损失项：其中S_i是i向(x, y, or z) 动量源项，D和C是规定的矩阵。
在多孔介质单元中，动量损失对于压力梯度有贡献，压降和流体速度(或速度方阵)成比例。
对于简单的均匀多孔介质：其中a是渗透性，C_2时内部阻力因子，简单的指定D和C分别为对角阵1/a 和C_2其它项为零。
FLUENT®允许模拟的源项为速度的幕率：其中C_0和C_1为自定义经验系数。
注意：在幕律模型中，压降是各向同性的，C_0的单位为国际标准单位。
fluent多孔跳跃模型参数设置
fluent多孔跳跃模型参数设置摘要：I.引言A.简介B.多孔跳跃模型在Fluent 中的重要性II.多孔跳跃模型的参数设置A.模型类型及选择1.简介2.选择合适的模型类型B.参数设置1.空隙率2.热导率3.密度和比热容4.粘性阻力和内部阻力C.燃烧patch 个温度III.设置多孔介质区域A.空隙率B.热导率和密度C.粘性阻力和内部阻力D.旋转轴和/或区域运动IV.总结A.重新审视多孔跳跃模型参数设置的重要性B.未来发展趋势和挑战正文：Fluent 是一款广泛应用于流体、热传递和化学反应等领域的商用CFD 软件包。
在Fluent 中，多孔跳跃模型是一种重要的模型类型，它可以用于描述流体在多孔介质中的流动行为。
为了准确地模拟这种流动行为，我们需要正确地设置多孔跳跃模型的参数。
首先，我们需要选择合适的模型类型。
Fluent 提供了多种多孔跳跃模型类型，如Darcy 模型、Forchheimer 模型等。
选择合适的模型类型是成功模拟多孔介质流动的关键。
不同的模型类型适用于不同的流体和流动条件，因此，我们需要根据实际问题来选择最合适的模型类型。
接下来，我们需要设置多孔跳跃模型的参数。
这些参数包括空隙率、热导率、密度和比热容、粘性阻力和内部阻力等。
空隙率是描述多孔介质中空隙体积与总体积之比的重要参数。
热导率和密度是影响多孔介质热传递性能的重要参数。
比热容、粘性阻力和内部阻力则影响了流体在多孔介质中的流动特性。
在设置多孔介质区域时，我们需要考虑空隙率、热导率和密度等参数。
此外，我们还需要设置旋转轴和/或区域运动等参数。
这些参数将影响多孔介质中的流动行为，因此，我们需要仔细地设置这些参数。
总之，Fluent 中的多孔跳跃模型参数设置是一个复杂的过程，需要我们仔细地选择模型类型、设置参数并考虑多方面的影响因素。
只有正确地设置这些参数，我们才能成功地模拟多孔介质中的流动行为。
未来，随着多孔介质的应用领域不断扩大，多孔跳跃模型的参数设置将面临更多的挑战。
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多孔介质是由多相物质所占据的共同空间，也是多相物质共存 的一种组合体，没有固体骨架的那部分空间叫做孔隙，由液体或气 体或气液两相共同占有，相对于其中一相来说，其他相都弥散在其 中，并以固相为固体骨架，构成空隙空间的某些空洞相互连通。
多孔介质模型可以应用于很多问题，如通过充满介质的流动、 通过过滤纸、穿孔圆盘、流量分配器以及管道堆的流动。
用Van Winkle方程计算带方孔的多孔板上压强的损失。方程的 提出者认为该方程适用于呈三角形分布的等距方孔板的湍流计算，具 体形式如下：
式中m为通过板的质量流量，fA为孔的总面积，pA板的总面积(固体 与孔的和)，D/ t孔直径与板厚之比,C是随雷诺数和D/t变化的系数，其 值可以通过查表获得。在t/D>1.6,且Re>4000时，C近似等于0.98，其中 雷诺数是用孔的直径做特征长，孔中流体的速度做特征速度求出的。
多孔介质模拟 方法是将流动区域 中固体结构的作用 看作是附加在流体 上的分布阻力。
动量方程 能量方程的处理 阻力系数的推导 操作步骤（实例）
后处理
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计算流体力学控制方程
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时间项
对流项 变数
扩散项 扩散系数 0
D 0 0 C 0 C11 C 13 v x 12 13 vx x 1 D 0 v v C 0 C C 0 23 y 22 22 23 v y y 21 2 C D33 C 0 C33 31 32 33 v z z vz 0
△Py, △Pz分别是x,y,z三个方向的压力降。△nx, 别是多孔介质在x,y,z三个方向的真实厚度。
△Px,
△
ny,△nz分源自6多孔介质的源项多孔中的惯性损失：在高速流动中，多孔介质动量源项中的常 数C2 可以对惯性损失作出修正。 C2可以看成沿着流动方向每一单 位长度的损失系数，因此允许压降指定为动压头的函数。 如果模拟的是穿孔板或者管道堆，有时可以消除渗透项而只是 用内部损失项，从而得到下面的多孔介质简化方程：
其中Si是i向(x,y,z)动量源项，D和C是规定的矩阵。在多孔介 质单元中，动量损失对于压力梯度有贡献，压降和流体速度（或速 度平方）成比例。
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广义源项 源项 S 0
方程
连续性方程 X-动量方程 Y-动量方程 Z-动量方程 能量方程
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p / x SM x
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p / z SM z
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动量方程
通用形式： 帮助文件：
is external body forces . also contains other modelDv terms such as porous-media 2 and userdependent source Fb p 2 S v 流体力学 ： defined sources. Dt 3
div u div grad S t
运动方程：
Dv Fb p f Dt
惯性力 品质力 表面力
多孔介质模拟方法是将流动区域中固体结构的 作用看作是附加在流体上的分布阻力。
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多孔介质的源项
多孔介质的作用是在动量方程中增加一个源项来模拟，源项由两 部分组成：一个粘性损失项和一个惯性损失项。
在计算层流时，上式中右端第二项可以被去掉，Ergun方程随之 简化为Blake-Kozeny方程：
在上述方程中μ 为粘度，Dp为粒子的平均直径，L为床的深度,ε 为空腔比率,定义为空腔与填充床的体积比。对比多孔介质的源项方 程，各方向上的渗透率和惯性损失系数为：
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用经验公式推导穿过多孔板的流动参数
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多孔介质模型应用
我们为什么要应用多孔介 质模型？
基于多孔介质模型的数值模拟方 法最初被用于模拟换热器和核反应 堆中流体的流动和传热问题。换热 器中存在大量的换热管道和阻碍片, 要模拟具有500根换热管和10个阻碍 片的换热器中的流动,将需要1.5亿 个网格单元 ,这大大超出了目前计 算机的计算能力。 为此,PatankarSpalding提出了采 用分布阻力的方法,也称为多孔介质 模型的方法。之后sha等采用这种方 法模拟了蒸汽发生器和核反应堆堆 芯中流体的流动, Karayannis等模 拟了换热器中的流动,Prithiviraj 和Andrews模拟了三维换热器中的流 动。
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阻力系数推导
采用已知的压强损失，基于名义速度推导多
孔介质参数
采用Ergun方程计算充填床的多孔介质参数 用经验公式推导穿过多孔板的流动参数
用表格数据计算流过纤维垫的多孔介质参数
用压强和速度的实验数据计算多孔介质系数
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采用Ergun方程计算充填床的多孔介质参数
在湍流中，充填床的数学模型是用穿透率和惯性损失系数来定义 的。计算相关常数的一种办法是使用半经验公式Ergun方程，这个方 程适用的雷诺数范围很广，同时也使用于多种填充物：
对于简单的多孔介质，只保留D和C矩阵的对角线元素。 对于简单的、各向同性的多孔介质，各个方向的阻力特性一样， 对角线元素相等。
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多孔介质的源项
在多孔介质单元中，动量损失对于压力梯度有贡献，压降和流 体速度（或速度平方）成比例。 多孔介质的Darcy定律：通过多孔介质的层流流动中，压降和 速度成比例，常数C2 可以考虑为零。忽略对流加速以及扩散。
△Py, △Pz分别是x,y,z三个方向的压力降。△nx, 别是多孔介质在x,y,z三个方向的真实厚度。
△Px,
△
ny,
△
n z分
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能量方程的处理
能量方程：
多孔介质对能量方程修正：
对于多孔介质流动，FLUENT仍然解标准能量输运方程，只是修改 了对流项和时间导数项。对对流项的计算采用了有效对流函数，时间 导数项则计入了固体区域对多孔介质的热惯性效应。 多孔区域的有效热传导率keff是由流体的热传导率和固体的热传 导率的体积平均值计算得到：