ANSYS CFX-Mesh Tutorials phần 5 pptx

To select the blunt body, you can click on Blunt Body in the Tree View, under “2 Parts, 2 Bodies”.. Select the Body Composite 2D Region by clicking on its name in the Tree View.. Generat

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1 Select Create>Body Operation from the Menu Toolbar.

2 Set Type to Cut Material and Bodies to the blunt body To select the blunt body, you can click on Blunt

Body in the Tree View, under “2 Parts, 2 Bodies”.

3

Click on Generate to remove the blunt body from its containing box.

The geometry is now complete

1 Select File>Save to save the geometry file.

2 Mesh Generation

First open CFX-Mesh

1 Switch from DesignModeler to the Project Page using the tabs at the top of the window, and click on

Generate CFX Mesh to open CFX-Mesh.

Setting up the Regions

Create the region for the inlet:

1 Create a Composite 2D Region called Inlet.

2 Select the rectangular face of the solid with the lowest X-coordinate to apply it to

Create the region for the outlet:

1 Create a Composite 2D Region called Outlet.

2 Select the rectangular face of the solid with the highest X-coordinate to apply it to

Create the region for the top free-slip wall:

1 Create a Composite 2D Region called Free1.

2 Select the rectangular face of the solid with the highest Z-coordinate to apply it to

Create the region for the side free-slip wall:

1 Create a Composite 2D Region called Free2.

2 Select the rectangular face of the solid with the lowest Y-coordinate to apply it to

Create the region for the symmetry plane:

1 Create a Composite 2D Region called SymP.

2 Select the rectangular face of the solid with the highest Y-coordinate to apply it to

It is a good idea to create a separate region on the surface of the blunt body for visualization purposes and for setting mesh controls

1 Create a Composite 2D Region called Body.

2 You need to select the nine faces of the blunt body to apply this to This can be done using Box Select: whilst holding down the left mouse button, drag a box across the body surfaces (as shown in the picture Tutorial 5: Blunt Body

CFX-Mesh Tutorials © SAS IP, Inc.

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below) to select them All the surfaces which are fully enclosed in this box will be selected Press Apply

in the Details View to accept the selection

Setting up the Mesh

Set the Maximum Spacing:

1 Click on Default Body Spacing in the Tree View, which is contained in Mesh>Spacing.

2 In the Details View, change Maximum Spacing to 0.8 m, and press Enter on the keyboard to set this

value

It is desirable to have a reasonably fine mesh around the surfaces of the blunt body You can create a Face Spacing

to concentrate nodes and elements in this region

1 Right-click on Spacing and select Insert>Face Spacing

2 Select the Body Composite 2D Region by clicking on its name in the Tree View Click on Apply in the

Details View

3 In the Details View, set Face Spacing Type to Constant, and set the Constant Edge Length to 0.15 m.

This sets the mesh length scale for the Face Spacing

4 Set the Radius of Influence to 0.0 m, and Expansion Factor to 1.2.

You can use Inflation to produce a thin layer of prismatic elements around the body external surface and along the ground

1 Click on Inflation in the Tree View In the Details View, set Number of Inflated Layers to 5.

2 Set Expansion Factor to 1.3.

3 In the Tree View, right-click on Inflation and select Insert>Inflated Boundary.

4 For Location, select both Body and Default 2D Region from the Tree View Hold down the Ctrl key in

order to select the second of these

5 Set Maximum Thickness to 0.1 m.

Generating the Surface Mesh

Obtain a view of the surface mesh over the surface of the blunt body using a Preview Group:

Section 2: Mesh Generation

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1 Right-click over Preview in the Tree View, and select Insert>Preview Group Change the name of the Preview Group to Body.

2 For Location, select the Composite 2D Region Body from the Tree View.

3 Now right-click over the Preview Group Body in the Tree View, and select Generate This Surface Mesh.

The surface mesh will be generated on just the corresponding faces

Next, take a look at the mesh on the symmetry plane:

1 Right-click over Preview in the Tree View, and select Insert>Preview Group Change the name of the Preview Group to SymP.

2 For Location, select the Composite 2D Region SymP from the Tree View.

3 Now right-click over the Preview Group SymP in the Tree View, and select Generate This Surface Mesh.

The surface mesh will be generated on just the corresponding faces

4 Click on the green Y-axis in the triad at the bottom right of the Model View to put the geometry into a good viewing position to inspect this mesh, and click on the Preview Group in the Tree View to display it

5 Zoom into the region of mesh near the front of the Blunt Body (as shown in the picture below), using the right mouse button to drag a box to define the required viewing area

If you look at the inflation layers between the Body and the Ground (bottom), then you will see that there was not enough space for the mesher to add the full five layers of inflation (you may need to zoom in more to be able to see this) To see why this happens, display the mesh as it was before the inflated layers were generated

1 Click on Preview in the Tree View, and in the Details View, set Display Mesh to Mesh Before Inflation.

Re-display the Preview Group by clicking on its name in the Tree View

Tutorial 5: Blunt Body

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You can now see that the gap between the Body and the ground is only around one to two elements thick, given the mesh spacing round the Body Since the total height of the Inflation Layers would be approximately one element thick on each side of the gap, this explains why there is not enough room for the full 5 layers of inflation that you set

To avoid this problem without having to explicitly set a Face Spacing in the location of the small gap, you can use Surface Proximity Surface Proximity is a meshing feature that detects close surfaces, such as the base of the body and the ground, and then refines the mesh so that a minimum number of mesh elements span the gap The default number of elements across the gap is 4, and this is the minimum recommended when both faces have inflation, such as in this case

You can turn on Surface Proximity as follows:

1 Click on Proximity in the Tree View.

2 Set Surface Proximity to Yes and change the Number of Elements Across Gap to 3.

The value of 3 is lower than is generally recommended, in order to keep the mesh small for the tutorial

1 Regenerate the mesh on the Preview Group SymP by right-clicking on its name in the Tree View and selecting Generate This Surface Mesh.

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You will see that 3 elements now span the gap The surface mesher has detected the close proximity of the two surfaces and refined the mesh in this region, leading to elements of a higher quality

Surface Proximity is an automatic method that produces higher quality meshes for many geometries However, you should always check the size of the mesh produced, as it can dramatically increase the number of nodes In some cases it is important to use a minimum edge length to prevent over-refinement of the mesh; see the CFX-Mesh Help under Surface Proximity for more details

Set the Preview options back to show the inflated layers:

1 Click on Preview in the Tree View, and in the Details View, set Display Mesh to Mesh After Inflation.

Re-display the Preview Group by clicking on its name in the Tree View

Tutorial 5: Blunt Body

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You can now see that the full five layers of inflation are present A better quality mesh would have been achieved

if the default setting of Number of Elements Across Gap (4) had been retained.

Generating the Volume Mesh

Finally, you can generate the volume mesh

1 Right-click on Mesh in the Tree View and select Generate Volume Mesh.

2 Save the GTM File as BluntBodyMesh.gtm.

The mesh is now complete

1 Select File>Save to save the CFX-Mesh database.

2 Switch to the Project Page using the tabs at the top of the window, and choose File>Save to save the

project

If you want to continue by working through the CFX-5 example “Tutorial 5: Flow Around a Blunt Body” using the newly-generated mesh, and have CFX-5.7.1 in ANSYS Workbench installed on your machine, then follow these steps:

1 On the Project Page, a new entry will have appeared when you generated the file: Advanced CFD Under this entry, double-click on BluntBodyMesh.gtm to open up CFX-Pre.

2 Once CFX-Pre has opened, choose File>Save Simulation As to save the simulation as BluntBody.

3 Work through the CFX-5.7.1 tutorial, missing out the instructions in the sections “Creating a New Simu-lation” and “Importing a Mesh”

If you do not have CFX-5.7.1 in ANSYS Workbench installed or do not want to work through the CFX-5 example, then:

1 Exit from ANSYS Workbench by selecting File>Exit.

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Tutorial 6: Butterfly Valve

This example creates the geometry and mesh for a butterfly valve in a pipe The following geometry and meshing features are illustrated:

• Parasolid import of the valve geometry;

• splitting the geometry along a line;

• curvature-sensitive meshing;

• Face Spacing, for refining the mesh on a particular face;

• Inflation;

• Proximity, for refining the volume mesh when two faces are close together; and

• Preview Groups, for previewing part of the surface mesh

This tutorial requires you to have a copy of the Parasolid file PipeValve.x_t If you do not already have this file,

then:

• On a Windows machine, download it here (you will need to execute the downloaded file to extract the required Parasolid file)

• On a UNIX machine, download it here (you will need to use “gunzip” to extract the required Parasolid file)

If you want to skip the geometry creation part of the tutorial, then see the instructions in Introduction to the CFX-Mesh Tutorials

1 Geometry Creation

Creating the Project

1 Open ANSYS Workbench, and create a new empty project Save it as PipeValve.wbdb.

2 Choose New Geometry and open up DesignModeler, specifying the units as millimeters.

Setting up the Valve Geometry

The first step is to import the valve geometry

1 Select File>Import External Geometry File from the Menu Toolbar.

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2 In the file browser which opens, locate the file PipeValve.x_t and choose to Open it (If you have not

already got this file, refer to the introduction to this tutorial for details of where to find it.)

3

Click on Generate to import the valve.

The valve is imported with its flat faces parallel to the ZXPlane For the simulation, it needs to be tilted at an angle

of 35 degrees, so the next step is to move it In DesignModeler, the way to move a body is to move it from one plane to another So first you need to create the new plane, and then use a Body Operation to transform the valve

1

Create a new plane ( ), based on the ZXPlane

2 In the Details View, set Transform 1 to Rotate about Global X, and set the Value of the rotation to -35

degrees

3

Click on Generate to create the plane.

5 Set Type to Move and select the valve as Bodies To select the valve, you can click on it in the Model

View

6 Set Source Plane to ZXPlane and Destination Plane to Plane4.

7

Click on Generate to move the valve.

8 Click on ZXPlane to show the original plane, so that you can see how the valve has moved.

Creating the Pipe

You now need to create the pipe which surrounds the valve, in which the fluid flows To stop the new solid from merging with the valve, first you must freeze the valve solid, and you will also give it a name to identify it more easily later on

1 In the Tree View, click on the plus sign next to “1 Part, 1 Body” and then select Solid from the tree

under-neath this entry In the Details View, you will now see the information relating to the body Click on the word “Solid” in this information, and change it to read “Valve” Pressing Enter on the keyboard will let the name change take effect

Tutorial 6: Butterfly Valve

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2 Select Tools>Freeze from the Menu Toolbar to freeze the valve.

3

Create a new plane ( ), based on the XYPlane

4 In the Details View, set Transform 1 to Offset Z, and set the Value of the offset to -100 mm.

5

Click on Generate to create the plane You may need to zoom out from the valve geometry to see

the new plane

6

Create a new sketch ( ) based on the new plane, Plane5

7 Use Circle from the Draw Toolbox of the Sketching tab to draw a circle in the new sketch, centered on

the origin and with radius 20 mm

8

Select Extrude from the 3D Features Toolbar.

9 Set Base Object to be the new sketch (Sketch1), and set Operation to Add Material.

10

Set Depth to be 200 mm, and click on Generate to create the pipe.

Now you can subtract the solid material in the valve from the pipe, to leave a valve-shaped hole in the pipe The remaining solid is exactly the volume in which fluid flows, ready to set up a simulation of fluid flow past the valve

2 Set Type to Cut Material and Bodies to the valve To select the valve, you can click on Valve in the Tree

View, under “2 Parts, 2 Bodies”

3

Click on Generate to remove the valve material from the pipe.

Although it is not easy to see, the pipe now has a valve-shaped hole in it

Splitting the Solid

Since this model exhibits symmetry about the YZPlane, you can divide it in two using a slice operation, and then run the simulation on only one half, to reduce the computing resources required The slice operation can only

be used on geometry which is frozen

1 Select Tools>Freeze from the Menu Toolbar.

Section 1: Geometry Creation

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2 Create a new sketch based on Plane5.

3 Use Line from the Draw Toolbox of the Sketching tab to draw a single vertical line in the new sketch,

along the Y-axis The exact dimensions of the line are not important but the line must extent above the top of the geometry (Y = 20 mm) and below the bottom of the geometry (Y = -20 mm)

4

Select Extrude from the 3D Features Toolbar.

5 Set Base Object to be the new sketch (Sketch2), and set Operation to Slice Material.

6

Set Depth to be 200 mm, and click on Generate to split the pipe.

8 Set Type to Delete and Bodies to the half of the pipe which has its X-coordinate positive, by clicking

on it in the Model View

9

Click on Generate to remove the unwanted half of the pipe.