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1.2. Prerequisites

This tutorial is written with the assumption that you have completed one or more of the introductory tutorials (Fluid Flow and Heat Transfer in a Mixing Elbow (p. 35), for example) found in this manual and that you are familiar with the ANSYS Fluent outline view and ribbon structure. Some steps in the setup and solution procedure will not be shown explicitly.

1.3. Problem Description

The manifold modeled here is shown in Figure 1.1: Manifold Geometry for Flow Modeling (p. 2). Air flows through the three inlets with a uniform velocity of 10 m/s, and then exits through the outlet.

Figure 1.1: Manifold Geometry for Flow Modeling

1.4. Setup and Solution

The following sections describe the setup and solution steps for this tutorial:

1.4.1.Preparation

1.4.2.Meshing Workflow

1.4.3.General Settings

1.4.4.Solver Settings

1.4.5.Models

1.4.6.Materials

1.4.7.Cell Zone Conditions

1.4.8.Boundary Conditions

1.4.9.Solution

1.4.10.Postprocessing

1.4.1. Preparation

To prepare for running this tutorial:

1.Download the exhaust_manifold.zip file here.

2.Unzip manifold.zip to your working directory.

The SpaceClaim CAD file manifold.scdoc can be found in the folder. In addition, the manifold.pmdb file is available for use on the Linux platform.

3.Use Fluent Launcher to start the 3D version of ANSYS Fluent.

4.Ensure that the Display Mesh After Reading option is enabled.

5.Enable Double Precision.

6.Enable Meshing Mode.

7.Ensure Parallel is selected under Processing Options.

8.Set Processes to 4.

1.4.2. Meshing Workflow

1.Start the meshing workflow.

a. In the Workflow tab, select the Watertight Geometry workflow.

b. Review the tasks of the workflow.

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Each task is designated with an icon indicating its state (for example, as complete, incomplete, etc. For more information, see Understanding Task States in the Fluent User's Guide). All tasks are initially incomplete and you proceed through the workflow completing all tasks. Additional tasks are also available for the workflow. For more information, see Customizing Workflows in the

Fluent User's Guide.

2.Import the CAD geometry (manifold.scdoc).

a.Select the Import Geometry task.

b.For Units, keep the default setting as mm.

c.(optional) Enable Advanced Options to expose additional options that may be required when importing a CAD geometry.

In this tutorial, we are keeping the default settings, so you can deselect the Advanced Options.

Many workflow tasks have advanced options that you may want to inspect before updating a task.

d.For File Name, enter the path and file name for the CAD geometry that you want to import (manifold.scdoc).

Note

The workflow only supports *.scdoc (SpaceClaim) and the intermediary *.pmdb file formats.

e.Select Import Geometry.

This will update the task, display the geometry in the graphics window, and allow you to proceed onto the next task in the workflow.

Note

Alternatively, you can use the … button next to File Name to locate the CAD geometry file, after which, the Import Geometry task automatically updates, displaying the geometry in the graphics window, and the workflow automatically progresses to the next task.

Throughout the workflow, you are able to return to a task and change its settings using either the Edit button, or the Revert and Edit button. For more information, see Editing Tasks in the Fluent User's Guide

3.Add local sizing.

a.In the Add Local Sizing task, you are prompted as to whether or not you would like to add local sizing controls to the faceted geometry.

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b.For the purposes of this tutorial, you can keep the default setting of no.

c.Click Update to complete this task and proceed to the next task in the workflow.

4.Create the surface mesh.

a.In the Create Surface Mesh task, you can set various properties of the surface mesh. for the faceted geometry.

b. For the purposes of this tutorial, you can keep the default settings.

Note

The red boxes displayed on the geometry in the graphics window are a graphical representation of size settings. These boxes change size as the values change, and they can be hidden by using the Clear Preview button.

c. Click Create Surface Mesh to complete this task and proceed to the next task in the workflow.

5.Describe the geometry.

When you select the Describe Geometry task, you are prompted with questions relating to the nature of the imported geometry.

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a.Since we plan on extracting a fluid region from this solid model, and adding capping surfaces, for the purposes of this tutorial, you can keep the default settings.

b.Click Describe Geometry to complete this task and proceed to the next task in the workflow.

6.Cover any openings in your geometry.

Select the Enclose Fluid Regions (Capping) task, where you can cover, or cap, any openings in your geometry in order to later extract the enclosed fluid region.

a.Create a cap for the inlets.

i.In the Name field, assign a name for the capping surface (for example, inlet) to be assigned to all of the manifold's inlets.

ii.For the Zone Type, keep the default setting of velocity-inlet.

iii.For the Select By field, keep the default setting of label.

iv.In the Labels list, select in1, in2, and in3 for the openings that you want to cover.

The graphics window indicates the selected items.

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v.Click Enclose Fluid Regions (Capping) to complete this task and proceed to the next task in the workflow.

Once completed, this particular task will return you to a fresh task in order to assign additional capping surfaces, if necessary. We will proceed to assign a cap for the remaining opening

and assign it to be an outlet.

b.Create a cap for the outlet.

i.In the Name field, assign a name for the capping surface (for example, outlet) to be assigned to the manifold's outlet.

ii.For the Zone Type, change the setting to pressure-outlet.

iii.For the Select By field, keep the default setting of label.

iv.In the Labels list, select out1 for the outlet that you want to cover.

v.Click Enclose Fluid Regions (Capping) to complete this task.

Now, all of the openings in the geometry are covered.

7. Create the fluid region.

a.Select the Create Regions task, where you can determine the number of fluid regions that need to be extracted. ANSYS Fluent attempts to determine the number of fluid regions to extract automatically.

b.For the Estimated Number of Fluid Regions, keep the default selection of 1.

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c. Click Create Regions.

8.Update your regions.

a.Select the Update Regions task, where you can review the names and types of the various regions that have been generated from your imported geometry, and change them as needed.

b.Keep the default settings, and click Update Regions.

Aside from fluid regions, and solid regions, you can also have voids within your geometry that are designated as dead regions. As you can see, there are four dead regions (corresponding to the four bolt holes near the outlet that were covered when the outlet was covered), a solid region, and a fluid region.

Once the regions have been updated, the fluid region is displayed by default in the graphics window. You can use the Draw Regions button to display other options, such as drawing just the solid region, just the dead regions, or all regions.

9.Create the volume mesh.

a.Select the Create Volume Mesh task, where you can set properties of the boundary layer mesh, as well as properties of the volume mesh itself.

b.Keep the default settings, and click Create Volume Mesh.

ANSYS Fluent will apply your settings and proceed to generate a volume mesh for the manifold geometry. Once complete, the mesh is displayed in the graphics window and a clipping plane is automatically inserted with a layer of cells drawn so that you can quickly see the details of the volume mesh.

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10.Check the mesh.

Mesh → Check

11.Save the mesh file (manifold.msh.gz).

File → Write → Mesh...

12.Save the case file (manifold.cas.gz).

File → Write → Case...

13.Switch to Solution mode.

Now that a high-quality mesh has been generated using ANSYS Fluent in meshing mode, you can now switch to solver mode to complete the set up of the simulation.

We have just checked the mesh, so select Yes when prompted to switch to solution mode.