1、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 throu
2、gh the porous medium.4. Enable reactions for the porous zone, if appropriate, and select the reaction mechanism.5. Enable theRelative Velocity Resistance Formulation. By default, this option is already enabled and takes the moving porous media into consideration (as described in Section7.19.6).6. Se
3、t the viscous resistance coefficients (in Equation7.19-1, orin Equation7.19-2) and the inertial resistance coefficients (in Equation7.19-1, orin Equation7.19-2), and define the direction vectors for which they apply. Alternatively, specify the coefficients for the power-law model.7. Specify the poro
4、sity 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
5、 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 mo
6、tion, 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 the coefficientsandin Equation7.19-3instead of the resistance coefficients and flow
7、 direction.You will set all parameters for the porous medium in theFluidpanel(Figure7.19.1), which is opened from theBoundary Conditionspanel(as described in Section7.1.4).Figure 7.19.1:TheFluidPanel for a Porous ZoneDefining the Porous ZoneAs mentioned in Section7.1, a porous zone is modeled as a s
8、pecial type of fluid zone. To indicate that the fluid zone is a porous region, enable thePorous Zoneoption in theFluidpanel. The panel will expand to show the porous media inputs (as shown in Figure7.19.1).Defining the Porous Velocity FormulationTheSolverpanel contains aPorous Formulationregion wher
9、e you can instructFLUENTto use either a superficial or physical velocity in the porous medium simulation. By default, the velocity is set toSuperficial Velocity. For details about using thePhysical Velocityformulation, see Section7.19.7.Defining the Fluid Passing Through the Porous MediumTo define t
10、he fluid that passes through the porous medium, select the appropriate fluid in theMaterial Namedrop-down list in theFluidpanel. If you want to check or modify the properties of the selected material, you can clickEdit.to open theMaterialpanel; this panel contains just the properties of the selected
11、 material, not the full contents of the standardMaterialspanel.If you are modeling species transport or multiphase flow, theMaterial Namelist will not appear in theFluidpanel. For species calculations, the mixture material for all fluid/porous zones will be the material you specified in theSpecies M
12、odelpanel. For multiphase flows, the materials are specified when you define the phases, as described in Section23.10.3.Enabling Reactions in a Porous ZoneIf you are modeling species transport with reactions, you can enable reactions in a porous zone by turning on theReactionoption in theFluidpanel
13、and selecting a mechanism in theReaction Mechanismdrop-down list.If your mechanism contains wall surface reactions, you will also need to specify a value for theSurface-to-Volume Ratio. This value is the surface area of the pore walls per unit volume (), and can be thought of as a measure of catalys
14、t loading. With this value,FLUENTcan calculate the total surface area on which the reaction takes place in each cell by multiplyingby the volume of the cell. See Section14.1.4for details about defining reaction mechanisms. See Section14.2for details about wall surface reactions.Including the Relativ
15、e Velocity Resistance FormulationPrior toFLUENT6.3, 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 (Section7.19.2).
16、 Using theRelative Velocity Resistance Formulationoption (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 with non-moving and moving porous media. Note thatFLUENTwill use the appro
17、priate velocities (relative or absolute), depending on your case setup.Defining the Viscous and Inertial Resistance CoefficientsThe viscous and inertial resistance coefficientsare both defined in the same manner. The basic approach for defining the coefficients using a Cartesian coordinate system is
18、 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 thedirectio
19、n 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 s
20、econd 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
21、the corresponding drop-down list when the UDF has been created and loaded intoFLUENT. Note that the coefficients defined in the UDF must utilize theDEFINE_PROFILEmacro. For more information on creating and using user-defined function, see the separate UDF Manual.If you are modeling axisymmetric swir
22、ling 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 pos
23、sible to define the coefficients using a conical (or cylindrical) coordinate system, as described below.Note that the viscous and inertial resistance coefficients are generally based on the superficial velocity of the fluid in the porous media.The procedure for defining resistance coefficients is as
24、 follows:1. Define the direction vectors. To use a Cartesian coordinate system, simply specify theDirection-1 Vectorand, for 3D, theDirection-2 Vector. The unspecified direction will be determined as described above. These direction vectors correspond to the principle axes of the porous media.For so
25、me problems in which the principal axes of the porous medium are not aligned with the coordinate axes of the domain, you may not know a priori the direction vectors of the porous medium. In such cases, the plane tool in 3D (or the line tool in 2D) can help you to determine these direction vectors.(a
26、) Snap the plane tool (or the line tool) onto the boundary of the porous region. (Follow the instructions in Section27.6.1or27.5.1for initializing the tool to a position on an existing surface.)(b) Rotate the axes of the tool appropriately until they are aligned with the porous medium.(c) Once the a
27、xes are aligned, click on theUpdate From Plane ToolorUpdate From Line Toolbutton in theFluidpanel.FLUENTwill automatically set theDirection-1 Vectorto the direction of the red arrow of the tool, and (in 3D) theDirection-2 Vectorto the direction of the green arrow. To use a conical coordinate system
28、(e.g., for an annular, conical filter element), follow the steps below. This option is available only in 3D cases.(a) Turn on theConicaloption.(b) Specify theCone Axis VectorandPoint on Cone Axis. The cone axis is specified as being in the direction of theCone Axis Vector(unit vector), and passing t
29、hrough thePoint on Cone Axis. The cone axis may or may not pass through the origin of the coordinate system.(c) Set theCone Half Angle(the angle between the cones axis and its surface, shown in Figure7.19.2). To use a cylindrical coordinate system, set theCone Half Angleto 0.Figure 7.19.2:Cone Half
30、AngleFor some problems in which the axis of the conical filter element is not aligned with the coordinate axes of the domain, you may not know a priori the direction vector of the cone axis and coordinates of a point on the cone axis. In such cases, the plane tool can help you to determine the cone
31、axis vector and point coordinates. One method is as follows:(a) Select a boundary zone of the conical filter element that is normal to the cone axis vector in the drop-down list next to theSnap to Zonebutton.(b) Click on theSnap to Zonebutton.FLUENTwill automatically snap the plane tool onto the bou
32、ndary. It will also set theCone Axis Vectorand thePoint on Cone Axis. (Note that you will still have to set theCone Half Angleyourself.)An alternate method is as follows:(a) Snap the plane tool onto the boundary of the porous region. (Follow the instructions in Section27.6.1for initializing the tool to a position on an existing surface.)
