26 Tutorial 2: Static Mixer (Refined Mesh) This example modifies the mesh and geometry for the static mixer example created in the previous example, and assumes that you have access to the files created as part of that example. The following geometry and meshing features are illustrated: • modifying an existing mesh setup; • Inflation, and • geometry update. 1. Modifying the Mesh Generation Opening the Existing Project 1. Open ANSYS Workbench. 2. In the main part of the window, click on the existing StaticMixer project. If it does not appear in the list of recent projects (perhaps because you moved the files), then use Browse to locate the project file StaticMixer.wbdb instead. 3. To open CFX-Mesh, double-click on StaticMixer. CFX-Mesh will now be opened with the geometry and mesh settings from the previous tutorial. Modifying the Mesh Settings The first step is to create a refined mesh size over the whole geometry. 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 0.2 m. This is a smaller length scale for the model than set previously (0.3 m). CFX-Mesh Tutorials . . © SAS IP, Inc. 3. Press Enter on the keyboard to set this value. The next step is to create an Inflated Boundary on the walls of the mixer. Creating inflated boundaries generates prismatic elements from the surface by inflating triangular elements into the solid. As a result, near the wall boundaries there will be layers of flat prismatic (wedge-shaped) elements which provide a smaller mesh length scale in the direction perpendicular to the wall. This provides better resolution of the velocity field near the wall, where it changes rapidly. Inflation can greatly improve accuracy, particularly in a model with a high aspect ratio, such as a long narrow pipe, or in a model where turbulence is significant. Inflation should always be used when you are interested in lift, drag or pressure drop in the model. Away from the wall boundaries, the mesh elements will be tetrahedral as they were in Tutorial 1. First, you will set the parameters used to control the inflation process, and then you will create the Inflated Boundary itself. 1. Click on Inflation in the Tree View. 2. In the Details View, set Number of Inflated Layers to 5. This will give five layers of prism elements. 3. Set Expansion Factor to 1.3. This controls how fast the thickness of the prism elements grows in suc- cessive layers away from the wall. 4. Leave the other settings as their default values. 5. In the Tree View, right-click on Inflation and select Insert>Inflated Boundary. 6. Click on Default 2D Region in the Tree View to select the faces which are in the Default 2D Region for the Inflated Boundary. Click on Apply in the Details View. The text should change to read 1 Composite. 7. Set Maximum Thickness to 0.2 m. This creates an Inflated Boundary that uses all the faces in the Default 2D Region. If you later change the 2D Region settings so that the Default 2D Region contains different faces, the Inflated Boundary will automatically update to always use the faces in the Default 2D Region at the time when the mesh is generated. Generating the Surface Mesh You will now have a look at the surface mesh to see the effect of the chosen length scale and the inflation, compared to the mesh you generated for the previous example. You can use the existing Preview Group to display the surface mesh. 1. Right-click over Default Preview Group and select Generate This Surface Mesh. Tutorial 2: Static Mixer (Refined Mesh) CFX-Mesh Tutorials . . © SAS IP, Inc. 28 You should be able to see that this mesh is finer (has more surface elements) that the mesh you generated in the first example. Also, note that there are triangular prism elements near the walls of the mixer vessel, the edges of which can be seen when you look at mesh on the two inlets or outlet. 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 StaticMixerRefMesh.gtm. The mesh is now complete. 1. Select File>Save to save the CFX-Mesh database. From this point, you could go straight into the CFX-5 example “Tutorial 2: Flow in a Static Mixer (Refined Mesh)” using the newly-generated mesh. However, this tutorial continues by modifying the geometry in order to illustrate how to set dimensions on geometry objects and how to tell CFX-Mesh to use the updated geometry. Setting dimensions is essential when creating geometry features which have dimensions which are not simple fractions of the model units, and so cannot use the grid for positioning the points and lines in the sketches. 29 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 1: Modifying the Mesh Generation 2. Geometry Modification In this section, you will change the radius of the inlet pipes to 0.4 m from the initial 0.5 m, without using the grid to position the circle. You will then extend the outlet pipes. 1. At the top of the ANSYS Workbench window, you should be able to see two tabs: StaticMixer [Project] and StaticMixer [CFX-Mesh]. Click on StaticMixer [Project] to return to the Project Page. 2. To open DesignModeler, double-click on StaticMixer. 3. Once DesignModeler has opened, click on the plus sign next to ZXPlane and then select Sketch2 in the Tree View, noting which circle it contains. Choose the Sketching tab. 4. Click on Dimensions (in the Sketching tab) to open the Dimensions Toolbox. 5. Click on Radius and then select the circle which forms Sketch2 from the Model View. 6. Click somewhere in the Model View to choose where the label for this dimension will be placed (this does not affect the model in any way, it is purely for display purposes). 7. If you now look in the Details View at the bottom left of the screen, you will find a section headed Dimen- sions, which contains the radius R1, set to 0.5 m. For now, change the radius to be 0.4 m . 8. Click on Generate to activate the change. You will see that both of the side pipes now have a reduced radius as required. The radius of both the pipes changed simultaneously as the property of AutoConstraints is turned on by default. This automatically detects dimensions which are equal and constrains them to be equal so that when one changes, the other does also. See the DesignModeler documentation for more details. You have now explicitly defined the dimension (radius) of the inlet pipe radii and can easily change it again if needed, perhaps if you change the geometry or if you made a mistake when originally specifying the radius. Whenever you are asked in later tutorials to create a geometry object of a particular size, you can either set up the grid to enable precise positioning of the geometry, or create the geometry at approximately the right size and then use the Dimensions Toolbox to specify the dimension exactly. Now you can extend the outlet pipe. The first part of the extension requires a Revolve operation. However, you need to revolve the end surface of the existing outlet pipe, which isn't currently defined as a sketch or plane, so first you need to construct the appropriate plane from which to revolve. 1. Create a new plane by using the New Plane ( ) button on the Active Plane/Sketch Toolbar, which is located above the Model View. 2. In the Details View, set Type to be From Face and Subtype to be Outline Plane. 3. In the Details View, click in the box next to Base Face. There will now be two buttons, Apply and Cancel, and this means that you are ready to select the face from the Model View. 4. In the Model View, click on the circular face at the end of the outlet pipe, which is at the position with the lowest value of the Z-coordinate. Click on Apply in the Details View. 5. Click on Generate to create the plane. The Revolve operation requires the specification of a rotation axis. Since this rotation will not be around any of the main coordinate axes, a sketch containing a single line to act as the required axis will be created. Tutorial 2: Static Mixer (Refined Mesh) CFX-Mesh Tutorials . . © SAS IP, Inc. 30 1. Select the new plane Plane4 in the Tree View again, and create a new sketch based on this plane by using the New Sketch ( ) button on the Active Plane/Sketch Toolbar, which is located above the Model View. 2. Select the Sketching tab. 3. Click on Settings (in the Sketching tab) to open the Settings Toolbox. 4. Click on Grid and turn ON Show in 2D and Snap. 5. Click on Major Grid Spacing and set it to 1. 6. Click on Minor-Steps per Major and set it to 2. 7. From the Draw Toolbox, select Line and then create a line which is parallel to the Y-axis and is positioned at x = 2 m. You can use the grid settings to position this line. The length of the line and the exact position of its end points are not important since it is only going to be used to define a rotation axis. 8. Select Revolve from the 3D Features Toolbar. 9. In the Details View, click next to Base Object and then click on the name of the plane that you have just created (Plane4) in the Tree View. Click Apply in the Details View. 10. In the Details View, click next to Axis and then click on the name of the sketch that you have just created (Sketch4) in the Tree View. Click Apply in the Details View. 11. Set Angle to 60 degrees. 12. Click on Generate to create the revolve. One more operation is needed to add another straight section of pipe to the outlet. This follows a very similar procedure to the one that you have just used to create the first extension. 1. Create a new plane by using the New Plane ( ) button on the Active Plane/Sketch Toolbar, which is located above the Model View. 2. In the Details View, set Type to be From Face and Subtype to be Outline Plane. 3. In the Details View, click in the box next to Base Face. There will now be two buttons, Apply and Cancel, and this means that you are ready to select the face from the Model View. 4. In the Model View, click on the circular face at the end of the newly revolved pipe section, which is in the position with the lowest value of the Z-coordinate. 31 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 2: Geometry Modification 5. Click on Generate to create the plane. 6. Select Extrude from the 3D Features Toolbar. 7. In the Details View, click next to Base Object and then click on the name of the plane that you have just created (Plane5) in the Tree View. Click Apply in the Details View. 8. Set Depth to 2 m. 9. Click on Generate to create the extrude. 3. Updating the Geometry in CFX-Mesh In this section you will make CFX-Mesh use the new geometry. 1. At the top of the ANSYS Workbench window, you should be able to see three tabs: StaticMixer [Project], StaticMixer [DesignModeler] and StaticMixer [CFX-Mesh]. Click on StaticMixer [CFX-Mesh] to return to the CFX-Mesh setup. Look closely at the Tree View. You should be able to see that many of the settings, including the top item (Model), have a green tick status symbol next to them, which means that the setup is completely valid. There are no yellow ticks and no red marks which indicate potential problems or an invalid setup. Any Preview Groups will have either a green tick ( ) or a green tick with a yellow flash ( ). In each case the green tick indicates that the setup is completely valid. The addition of the yellow flash indicates that the mesh which is displayed when you click on that Preview Group's name may not be up-to-date with the latest mesh settings i.e. you may have modified a setting since you last generated this surface mesh. 1. Right-click over Geometry in the Tree View. Select Update Geometry and click on Yes on the popup message to continue with the update. The Model View will refresh to show the new geometry, with the smaller radius pipes and the longer outlet. Also, the Tree View will be updated to account for the fact that whilst most geometry faces which were originally present are still there, one no longer exists (the original end of the outlet pipe) and there are some new ones (the sides and end of the new section of pipe). 1. Notice that the Tree View now shows that you have an invalid setup: various items show red exclamation marks ( ). The problem is that the specification for the 2D Composite Region “out” is invalid since the face it was applied to no longer exists. Tutorial 2: Static Mixer (Refined Mesh) CFX-Mesh Tutorials . . © SAS IP, Inc. 32 2. Click on out in the Tree View. Select the circular face at the bottom of the mixer vessel, with the lowest value of the Z-coordinate. 3. Click on Apply in the Details View. The model setup is now valid - the red status symbols have all gone from the Tree View. When you do a Geometry Update, any new faces are automatically added to the Default Preview Group and to the Default 2D Region. This means that you do not need to update Inflated Boundary 1 to include any new faces because it was set up to use the Default 2D Region as its location and the new faces will have been auto- matically added to this region. Sometimes when you do a Geometry Update, you will find that one or more yellow tick marks appear in the Tree View. This means that one or more faces was automatically removed from the corresponding meshing features as a result of the Geometry Update, because those faces no longer exist in the new geometry. The setup is still valid, however, because there is still at least one valid face used for that meshing feature. It is recommended that if you see yellow tick marks in your Tree View, you should check that the locations for the corresponding features are what you expect. The geometry has been successfully updated and the CFX-Mesh setup is ready to re-mesh. At this point you could create a new surface mesh or volume mesh. However, note that the CFX-5 example expects to use the original geometry, so you should ensure that you don't overwrite the original GTM File when creating the volume mesh. 1. Select File>Save to save the CFX-Mesh database. If you want to continue by working through the CFX-5 example “Tutorial 2: Flow in a Static Mixer (Refined Mesh)” 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 StaticMixerRefMesh.gtm to open up CFX-Pre. 2. Once CFX-Pre has opened, choose File>Save Simulation As to save the simulation as StaticMixerRef. 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. Choose to save all highlighted files. 33 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 3: Updating the Geometry in CFX-Mesh 34 Tutorial 3: Process Injection Mixing Pipe This example shows how to create a simple pipe junction, using Sweep to create the pipe profile. The following geometry and meshing features are illustrated: • Face Spacing, for refining the mesh on a particular face; • Inflation; and • full surface mesh generation, to preview the full surface mesh. 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, create a new empty project, and save it as InjectMixer.wbdb. If you need to, refer to the instructions in the Geometry Creation section of the Static Mixer tutorial for more details on how to do this. 2. Choose New Geometry to open DesignModeler, and specify the units as meters. Creating the Main Pipe To create the main pipe, you will use the Sweep operation. Sweep requires the use of two sketches: one defines the profile to be swept (in this case, a circle) and the other defines the path through which the profile is swept. The profile will be created first. CFX-Mesh Tutorials . . © SAS IP, Inc. [...]... the plane based upon it 2 In the Details View, set Transform 1 to Offset Global Z, and set the Value of the offset to 2 m 3 Set Transform 2 to Offset Global Y Set the Value of the offset to -3 m 4 Click on Generate to create the plane CFX-Mesh Tutorials © SAS IP, Inc 37 Tutorial 3: Process Injection Mixing Pipe 5 Create a new sketch ( 6 ) based on the new plane Use Circle from the Draw Toolbox of the... Select the circular face at the end of the small side pipe 3 Click on Apply in the Details View Create the region for the main inlet: 1 Create a Composite 2D Region called main inlet 2 Select the circular face at the end of the main pipe, with the lowest Z-coordinate 3 Click on Apply in the Details View Create the region for the outlet: 38 CFX-Mesh Tutorials © SAS IP, Inc Section 2: Mesh Generation 1... Geometry Modification section of the Static Mixer tutorial 7 Select Extrude from the 3D Features Toolbar 8 Set Base Object to be the new sketch (Sketch3), and set Operation to Add Material 9 Set Direction to Normal and Type to Fixed Set Depth to 3 m 10 Click on Generate to create the side-pipe Note that the extrusion of Sketch3 has to reach the main pipe body, but that it does not matter if it extends into... click on Undo (from the Undo/Redo Toolbar at the top of the ANSYS Workbench window) and try again, making sure that after you click on the first end point, you move the mouse in the correct direction for the arc that is to be drawn CFX-Mesh Tutorials © SAS IP, Inc Section 1: Geometry Creation Now make the pipe itself 1 Select Sweep from the 3D Features Toolbar 2 Set the Profile to be Sketch1: click...Tutorial 3: Process Injection Mixing Pipe 1 Create a new plane as follows Select the XYPlane in the Tree View and then click on the New Plane ) from the Active Plane/Sketch Toolbar, near the top of the ANSYS Workbench window icon ( Clicking on XYPlane first ensures that the new plane is based on the XYPlane 2 In the Details View, set Transform 1 (RMB) to Offset Z, and set the Value of the offset to -4 m 3. .. Right-click over Default Preview Group and select Generate This Surface Mesh You should be able to see that the mesh is finer around the side pipe than it is elsewhere in the geometry CFX-Mesh Tutorials © SAS IP, Inc 39 ... YZPlane active first by clicking on it, and then use the New Sketch icon to create the sketch based upon it 2 3 Set Major Grid Spacing to 1.0 m and Minor-Steps per Major to 2 4 Use Line from the Draw Toolbox of the Sketching tab to draw two straight lines on the sketch, as shown in the picture below 5 36 Use Grid from the Settings Toolbox of the Sketching tab to set Show in 2D and Snap to ON Click on Arc... meets another geometry object, but the net effect would be no different than using the Fixed extent 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 2 Click on the name of the DesignModeler entry, left of the Project Page InjectMixer, and then Generate... Click on 4 Generate to create the plane Create a new sketch as follows Select Plane4 in the Tree View and then click on the New Sketch icon ( ) from the Active Plane/Sketch Toolbar, near the top of the ANSYS Workbench window Clicking on the plane first ensures that the new sketch is based on Plane4 5 Use Grid from the Settings Toolbox of the Sketching tab to set Show in 2D and Snap to ON 6 Set Major... to control the size of the elements generated in the vicinity 1 Right-click on Spacing and select Insert>Face Spacing 2 Select the cylindrical face of the side pipe 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 0.05 m This sets the mesh length scale for the Face Spacing 4 Set the Radius of Influence to 0.0 m The mesh . example, then: 1. Exit from ANSYS Workbench by selecting File>Exit. Choose to save all highlighted files. 33 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 3: Updating the Geometry in CFX-Mesh 34 Tutorial 3: Process. the Value of the offset to 2 m. 3. Set Transform 2 to Offset Global Y. Set the Value of the offset to -3 m. 4. Click on Generate to create the plane. 37 CFX-Mesh Tutorials . . © SAS IP, Inc. Section. lowest Z-coordinate. 3. Click on Apply in the Details View. Create the region for the outlet: Tutorial 3: Process Injection Mixing Pipe CFX-Mesh Tutorials . . © SAS IP, Inc. 38 1. Create a Composite