A3                                      Porous Media 多孔介质In this tutorial we consider flow in a section of an automobile exhaust pipe, whose exhaust flow is resisted by two porous bodies serving as catalysts for transforming harmful carbon monoxide into carbon dioxide. When designing an automobile catalytic converter, the engineer faces a
compromise between minimizing the catalyst's resistance to the exhaust flow while maximizing the catalyst's internal surface area and duration that the exhaust gases are in contact with that surface area. Therefore, a more uniform distribution of the exhaust mass flow rate over the
catalyst's cross sections favors its serviceability. The porous media capabilities of FloEFD are used to simulate each catalyst, which allows you to model the volume that the catalyst occupies as a distributed resistance instead of discretely modeling all of the individual passages within the catalyst, which would be impractical or even impossible. Here, as a FloEFD tutorial example we consider the influence of the catalysts' porous medium permeability type (isotropic and
unidirectional media of the same resistance to flow) on the exhaust mass flow rate distribution over the catalysts' cross sections. We will observe the latter through the behavior of the exhaust gas flow trajectories distributed uniformly over the model's inlet and passing through the porous catalysts. Additionally, by coloring the flow trajectories by the flow velocity the exhaust gas
residence time in the porous catalysts can be estimated, which is also important from the catalyst effectiveness viewpoint.
在这个教程中，我们分析汽车排气管某一管段的流动，这个排气流动受到两个用于将有害一氧化碳转变成二氧化碳的多孔介质阻碍。
当设计汽车的催化转化器时，工程师要在最大化催化器内部表面的同时尽量减小催化器的排气阻力以及排气和表面接触持续时间两者之间寻求最佳点。因此，排出的气体质量流量在整个催化器截面上更为均匀的分布有助于它的使用性。
FloEFD 中的多孔介质可以仿真每一种催化器，允许你对催化器所占据的空间以分布式的阻力进行仿真，而不是对催化剂内所有独立通道进行分别仿真，因为这种方式是不符合实际情况甚至是不可能存在的。
在这个FloEFD 教程例子中我们考虑了催化剂多孔介质渗透类型（对于流动方向上等向性或非等向性的阻力）对整个催化器截面上排出的气体质量流量的影响。我们会观察到在排气后部的流动迹线分布比模型的入口处和穿过多孔介质时来的均匀。此外，依据流体速度对流动迹线赋予颜，排出流体在多孔催化剂中的阻力可以得到估计，从催化器的效率而言这一点也是很重要的。
Opening the Model 打开模型
1 Copy the A3 - Porous Media folder into your working directory and ensure that the files
are not read-only since FloEFD will save input data to these files.
复制“A3 - Porous Media”文件夹到你的工作目录并确认文件不是只读状态，因为FloEFD将会向保存其输入的
数据到这些文件。
2 Run  FloEFD. Click  File > Open .    运行FloEFD 。点击File > Open .
3 In the File Selection  dialog box, browse to the
catalyst.CATProduct  assembly located in the  A3 -
Porous Media folder and click Open .
在File Selection 对话框，浏览并打开在A3 - Porous Media  文
件夹中的catalyst.CATProduct 组件。
To skip the project definition and run the FloEFD project defined in accordance with the tutorial, you will
need to open the catalyst.CATProduct  assembly located in the A3 - Porous Media \Ready
folder and run the desired projects.
可以跳过项目定义，运行教程已定义的FloEFD 项目，您需要打开catalyst.CATProduct  (位于A3 - Porous Media\Ready 文件夹中，并运行所需项目。
Creating a FloEFD Project 创建FloEFD 项目
1 In the main menu click Insert > Wizard .Once inside the  Wizard ,type a project name:Isotropic.
The project Wizard guides you through the definition of the project’s properties step-by-step. Except for two steps (steps to define the project fluids and default solid), each step has some pre-defined values, so you can either accept these values (skipping the step by clicking Next ) or modify them to your needs.
这个项目向导会指导你一步一步完成整个项目的特性定义。除了其中两步（定义项目流体和默认固体），其他的每一步都是预先的定义值，所以你可以接受这些默认值（跳过这一步可以直接点击Next ）或者进行相应的修改。
These pre-defined settings are: 预定义设置是
unit system  – SI,
analysis type  – internal, no additional physical
capabilities are considered,
wall conditio n – adiabatic wall,
initial conditions  – pressure - 1 atm,
temperature - 293.2K.
For this project these default settings suit
perfectly and all what we need to do is just to select Air as the project fluid. To avoid passing through all steps we will use Navigator pane that provides a quick access to the Wizard’s pages.
对于这个项目所有的这些设置都是合适的，我们所要做的仅仅是将空气作为项目的流体。为了避免经过每一个向导
界面，我们将使用 Navigator 面板，它可以使我们快速的访问向导页。
2
Click an arrow  at the right.  点击右侧的箭头 3 In the Navigator  pane click Fluids .  在 Navigator 面板 ， 点击Fluids
Inlet
Outlet
Porous catalysts
多孔催化剂
.
4  Open the Gases folder, click Air, then click Add.  打开Gases文件夹，点击Air，接着点击Add。
5 Since we do not need to change other properties we can close the Wizard.
Click Finish in the Navigator panel.如果不需要改变属性，可以点击Finish直接
关闭导航器。
You can click Finish at any moment, but if you attempt to close Wizard without
specifying all obligatory properties (such as project fluids), the Wizard will not
close and the page where you need to define a missing property will be marked by
the exclamation icon
你可以在任何时候点击完成，但如果你想在没有定义完所有必须定义的特性（诸如项目流体）之
前关闭向导，这个向导将不能关闭并且在这个未做定义的向导页会出现一个感叹图标    .
Now FloEFD creates a new project with the FloEFD data attached.Right-click the
Computational Domain icon and select Hide/Show to hide the wireframe box.
现在 FloEFD 利用赋值数据的方式创建了一个新的例子。右击Computational Domain图标并且选择
Hide/S how来隐藏计算域黑线框。
Specifying Boundary Conditions 定义边界条件
1 In the FloEFD Analysis tree, right-click the Boundary Conditions icon and select Boundary
Condition object > New Boundary Condition.
在 FloEFD分析树中，右击Boundary Conditions图标并选择
Insert Boundary Condition 。
2 Select the inner face of the inlet lid as shown. 如图显示选择入口盖子的
内表面。
3 Select Flow Openings and Inlet Velocity.
4 Set the Velocity Normal to Face to 10 m/s.
5 Click OK.
With the definition just made, we told FloEFD that at this
opening air is flowing into the catalyst with a velocity of 10 m/s.
随着刚才所做的定义，我们告诉 FloEFD ：在这个开口处空气以10 m/s 的速度流进催
化器。
6 In the FloEFD Analysis tree, right-click the Boundary Conditions
icon and select Boundary Condition object > New Boundary
Condition. Select the inner face of the outlet lid as shown.  在
FloEFD分析树中，右击Boundary Conditions图标并选择Insert Boundary
Condition 。如图显示选择出口盖子的内表面。
7 Select Pressure Openings and Static Pressure.
8 Keep the defaults under Thermodynamic Parameters,
Turbulence Parameters, Boundary Layer and Options.
9 Click OK.
With the definition just made, we told FloEFD that at this
opening the fluid exits the model to an area of static atmospheric
pressure.随着刚才所做的定义，我们告诉 FloEFD 在这个开口处流体离开模型进入到
一个大气压的区域。
Now we can specify porous media in this project. To do this, first
we need to specify the porous medium’s properties (porosity,
permeability type, etc.) in the Engineering Database and then
apply this feature to the components in the assembly.
现在我们可以在这个项目中定义多孔介质。定义一个多孔介质，首先我们需要
在Engineering Database 中定义多孔介质的特性（多孔性，渗透类型等）之后应用
这一多孔介质到你的组件元件中。
Creating Isotropic Porous Medium in the Engineering Database
在工程数据库中创建一个等向性的多孔介质
The material you are going to create is already defined in the Engineering Database under the Pre-Defined folder. You can skip the definition of porous material and select the predefined "Isotropic" material from the Engineering database when you will assign the porous material to a component later in this tutorial.
pane你想要创建的材料已经在Engineering Database 下的Pre-Defined 文件夹中得到了定义。你也可以跳过多孔介质材料的定义，以后需要创建多孔介质特性时，直接从工程数据库中选择预定义的"Isotropic" 材料。
1 Click Tools > Engineering Database.
2 In the Database tree select Porous Media /User Defined.
3 Click New Item on the toolbar. The blank Item Properties
tab appears. Double-click the empty cells to set the corresponding
property values.
3. 点击工具栏上的 New Item 。这个空白 Item Properties 页出现。双击空白格去设定
相应的特性值。
4 Name the new porous medium Isotropic.命名这个新的多孔介质为 Isotropic。
5 Under Comment, click the  button and type the desired comments for this porous medium. The Comment property is optional, you can leave this field blank.
在 Comment，点击按钮并且输入对这个多孔介质的注释。这个 Comment 特性是可选择的，你也可以不做任何注释。
6 Set the medium’s Porosity to 0.5.设定这个介质的 Porosity 为 0.5。
Porosity is the effective porosity of the porous medium, defined as the volume fraction of the interconnected pores with respect to the total porous medium volume; here, the porosity is equal to 0.5. The porosity will govern the exhaust flow velocity in the porous medium channels, which, in turn, governs the exhaust gas residence in the porous catalyst and, therefore, the catalyst efficiency.
多孔性是指介质的有效多孔性，定义为互连孔相对于总介质体积的体积分量；在此，多孔性等于0.5。多孔性决定多孔介质通道排出气流的速率，反过来，多孔性也影响排出气流在催化剂内的分布，以及催化剂的效率。
7    Choose Isotropic as the Permeability type. 对 Permeability type 选择 Isotropic。
First of all let us consider an Isotropic permeability, i.e, a medium with permeability not depending on the direction within the medium. Then, as an alternative, we will consider a Unidirectional permeability, i.e., the medium permeable in one direction only.
首先我们来考虑一个 Isotropic 型渗透，也就是在介质内部其渗透性不会随着方向改变。之后，我们考虑一个Unidirectional 型渗透，也就是只能在一个方向上进行渗透。
8Choose Pressure drop, Flowrate, Dimensions as the Resistance calculation formula.选择Pressure drop， Flowrate， Dimensions 作为 Resistance calculation formula。

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