ANSYS CFX-Mesh Tutorials phần 6 ppsx

3. Change Inflation Option to First Layer Thickness, and set the First Prism Height to 0.5 mm. The pipe wall is to be modeled as a rough wall with an equivalent sand grain roughness of 0.2 mm. To maintain the validity of the assumptions used in modeling rough walls, it is important that the thickness of the first element off the wall is not much smaller than the equivalent roughness height. In general, a value equal to the roughness height is recommended, which would be 0.2 mm here. It is also important that the mesh length scale does not increase dramatically in the transition from the last inflation layer to the rest of the volume mesh. The value chosen here for the first prism height, combined with the high expansion factor, allows the elements in the inflation layers to expand to a reasonable size before the transition to the rest of the volume mesh. To produce a good mesh for this geometry, a much smaller Maximum Spacing is required, allowing a First Prism Height of 0.2 mm to be used and a smooth transition from the last inflation layer to the bulk volume mesh. 4. In the Tree View, right-click on Inflation and select Insert>Inflated Boundary. 5. For Location, select both pipe wall and Default 2D Region from the Tree View. Hold down the Ctrl key in order to select the second of these. Generating the Surface Mesh Next, take a look at the mesh on the pipe wall: 1. Right-click over Preview in the Tree View, and select Insert>Preview Group. Change the name of the Preview Group to pipe wall. 2. For Location, select the Composite 2D Region pipe wall from the Tree View. 3. Now right-click over the Preview Group pipe wall in the Tree View, and select Generate This Surface Mesh. The surface mesh will be generated on just the corresponding faces. 4. Click over the axes in the bottom right corner of the Model View in the position shown in the picture below. As you move the cursor into this position, the black “-X”-axis will appear (it is not shown by default). This will put the geometry into a good position for viewing the mesh. Tutorial 6: Butterfly Valve CFX-Mesh Tutorials . . © SAS IP, Inc. 68 Notice how the nodes are concentrated around the valve. 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 PipeValveMesh.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 9: Flow Through a Butterfly Valve” 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 PipeValveMesh.gtm to open up CFX-Pre. 2. Once CFX-Pre has opened, choose File>Save Simulation As to save the simulation as PipeValve. 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. 69 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 2: Mesh Generation 70 Tutorial 7: Catalytic Converter This example shows how to create the geometry and mesh for the inlet pipe and flange for a catalytic converter. The following geometry and meshing features are illustrated: • the Skin/Loft operation to extrapolate between sketch profiles; • Sketch Instances (copying and pasting an entire sketch); and • Inflation. 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 CatConv.wbdb. 2. Choose New Geometry to open DesignModeler, specifying the units as centimeters. Creating the Sketches for the Inlet Flange The first geometry operation will be to create four sketches to define the profile of the inlet flange. Two of the sketches are circles, and the other two consist of a more elongated shape constructed from eight edges (lines and curves). You will then use the Skin/Loft operation to connect the sketches. This operation requires that all sketches have the same number of edges, so the two circles will also have to be constructed with eight edges, and at an orientation which gives the smoothest connecting surface when the Skin/Loft operation is applied. 1. Create a new sketch ( ) based on the XYPlane. CFX-Mesh Tutorials . . © SAS IP, Inc. 2. Use Circle from the Draw Toolbox of the Sketching tab to create the circle centered on the origin with a radius of 2.5 cm. 3. To break the circle into eight edges, use the Modify Toolbox of the Sketching tab. Click on Split, then right-click on the Model View and select Split Edge into n Equal Segments. 4. Back on the Sketching tab, next to where you clicked on Split, you will now find a box which allows you to specify how many segments to break the circle into. Set it to 8 and select the circle in the Model View to perform the Split operation. To re-orient the circle to give a smoother final surface, you will move it round by 22.5 degrees. 1. Select Move from the Modify Toolbox. In the two boxes which appear, set the rotation angle r to be 22.5 degrees and leave the scale factor f unchanged. 2. Select all eight curves by clicking on them in turn (you don't need to hold down any mouse button to do this). 3. Right-click over the Model View and choose End/Use Plane Origin as Handle. This tells DesignModeler that you have finished selecting the edges to copy, and that you want to use the origin of the plane as a reference point for the rotation and the paste action which follows. 4. Right-click in the Model View and select Rotate by r Degrees to perform the rotation (you won't see any effect of this yet since it is only actually applied when you paste the circle into its new position). 5. Right-click again and select Paste at Plane Origin. You should see the original circle move round by 22.5 degrees. No translation took place since you pasted the reference point (the origin of the plane/center of the circle) back at the Plane Origin. 6. Right-click again and select End. The second sketch, Sketch2, is the second circle, placed in a different plane and made slightly bigger. Rather than constructing it from scratch and having to perform the Split and Move as you did for Sketch1, you will just copy it from Sketch1. 1. Create a new plane ( ), based on the XYPlane. 2. In the Details View, set Transform 1 to Offset Z, and set the Value of the offset to 1 cm. 3. Click on Generate to create the plane. Tutorial 7: Catalytic Converter CFX-Mesh Tutorials . . © SAS IP, Inc. 72 4. Right-click on Plane4 in the Tree View and select Insert>Sketch Instance. A Sketch Instance is just a copy of an ordinary sketch. 5. In the Details View, set Base Sketch to Sketch1. 6. Set Scale to 1.05. 7. Click on Generate to create the Sketch Instance. 8. To be able to see both sketches, right-click on each in turn in the Tree View, and select Keep Visible. You should now be able to see clearly both sketches, offset from each other and with the second one slightly larger than the first. The next sketch, Sketch3, is a different shape constructed of straight edges and quarter-circles. 1. Create a new plane ( ), based on the XYPlane. 2. In the Details View, set Transform 1 to Offset Z, and set the Value of the offset to 5 cm. 3. Click on Generate to create the plane. 4. Use Grid from the Settings Toolbox of the Sketching tab to set Show in 2D and Snap to on. 5. Set Major Grid Spacing to 5 cm and Minor-Steps per Major to 5. 6. Click on the Look At Plane/Face/Sketch icon ( ) to move the model to get a good view of the new plane. Zoom out a little by holding down the Shift key on the keyboard, pressing the middle mouse button and dragging the mouse downwards. 7. Use the Draw Toolbox of the Sketching tab to construct the shape shown below. For reference, the shape is 20 cm long and 12 cm high, and is orientated with the X-axis along the long axis of the shape. a. Use Line to draw the four straight edges. b. Use Arc by Tangent to draw the four quarter-circles. In each case, select the two end points of the arc. If the wrong part of the arc is being drawn (i.e. a 270 degree segment instead of a 90 segment) just before you click on the second end point, then right-click and select Reverse to correct it. Sketch4 is just a copy of Sketch3. 1. Create a new plane ( ), based on the XYPlane. 73 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 1: Geometry Creation 2. In the Details View, set Transform 1 to Offset Z, and set the offset to 6 cm. 3. Click on Generate to create the plane. 4. Right-click on Plane6 in the Tree View and select Insert>Sketch Instance. 5. In the Details View, set Base Sketch to Sketch3. 6. Set Scale to 1.05. 7. Click on Generate to create the Sketch Instance. 8. To be able to see all four sketches, right-click on the last two in turn in the Tree View, and select Keep Visible. Creating the Inlet Flange Having created all four profiles, you can now create the solid which connects them by using the Skin/Loft oper- ation. 1. Click on the blue Z-axis in the triad at the bottom right of the Model View to put the geometry into a good viewing position for the selection. 2. Select Skin/Loft from the 3D Features Toolbar. 3. Either: • Select the four profiles from the Model View by selecting the four edges shown in the picture below. You will need to hold down the Control key whilst selecting the second and subsequent edges. Select the edges in the correct order by taking the inside one first and then working outwards: the order of the profiles is important because the Skin/Loft operation will make a surface which smoothly in- terpolates between them in the order which you specify. or: • Select the four profiles from the Model View by holding down the left mouse button and placing the cursor in approximately the middle of the center circle. Whilst still holding down the left button, move the mouse slowly outwards towards the top left of the model view. As you pass over each sketch, it is selected and the edge that you passed the cursor over is highlighted. This automatically selects the sketches in the correct order (from inside to outside) which is important because the Skin/Loft operation will make a surface which smoothly interpolates between them in the order which you specify. Tutorial 7: Catalytic Converter CFX-Mesh Tutorials . . © SAS IP, Inc. 74 4. Click on Apply after selecting the four profiles. You will now be able to see some gray lines connecting the vertices of the profiles, one vertex from each. (Your gray lines may be in slightly different places, depending on exactly which edges you created first in the different sketches.) These lines are called guide lines, and give you a preview of how the Skin/Loft operation will connect these vertices. Unfortunately, the gray lines in the picture above indicate that the wrong vertices are being connected: if you went ahead and created the solid without fixing this, then the resulting shape would be very twisted. The correct way to join the vertices is shown in the picture below. Unless your vertices happen to be connected like the ones in the picture above, you will need to fix the problem, as described below. 75 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 1: Geometry Creation 1. Right-click and select Fix Guide Line. 2. Select different edges on the sketches until the gray lines look correct. Now continue to specify the settings for the Skin/Loft operation. 1. In the Details View for the Skin/Loft, set Merge Topology? to Yes. If you leave it as the default (No), then the solid which is created has 26 surfaces (a planar surface from the edges in Sketch1, a planar surface from the edges in Sketch4, and 24 surfaces for the smooth curved surfaces interpolated between the profiles). If you were to put a mesh onto this solid, then you would have to use a small mesh size to get a good quality mesh on and near the smallest surfaces. However, if you choose to Merge Topology directly in DesignModeler, then the resulting solid only has three surfaces: the smooth curved surface is created in one piece rather than 24 pieces. This solid can be meshed more evenly even with a coarser mesh size. 2. Click on Generate to create the Skin/Loft. The solid should look like the picture below when appropriately orientated. See the notes below if the solid does not look correct or if you get error messages when you generate it. If your solid is not correct, try the following. • Check that each of the four sketches has exactly eight edges, particularly if you get messages about profiles not having an equal number of edges. You can easily do this by selecting each sketch in the Tree View and reading the number of edges in the sketch from the Details View. • Check that you have selected the profiles in the right order, particularly if you get messages about self- intersecting geometry. You can check the order by viewing the Details View for the Skin/Loft; the profiles are listed in the order of selection. Only the order 1-2-3-4 or 4-3-2-1 will allow the solid to be generated correctly. If your profiles are in the wrong order, then fix this as follows: 1. Right-click on Skin1 in the Tree View and choose Edit Selections. 2. In the Details View, right-click on the name of the profile which is in the wrong order (e.g. Profile2), and use the commands Move to Top, Move up, Move down, and Move to Bottom to change the position of the profile. 3. Click on Generate to modify the Skin/Loft. • If you get a solid created which is very twisted, then check that the guide lines are correct: see above for details. Tutorial 7: Catalytic Converter CFX-Mesh Tutorials . . © SAS IP, Inc. 76 • If your solid is generated but looks to be the wrong shape, then you will have to check that each profile is correctly positioned, and that the planes you created (Plane4, Plane5 and Plane6) have the correct offsets and are all based on the XYPlane. You should also check that you have selected all four profiles and haven't missed one. Creating the Inlet Pipe You can now create the inlet pipe which attaches to the flange which you have just created. This is in two sections: a curved section and an extruded straight section. The curved section of the pipe is a Revolve operation based on Sketch1. However, you need to create a line to act as the axis for the rotation first. 1. Create a new sketch ( ) based on the XYPlane. 2. Use Line from the Draw Toolbox of the Sketching tab to draw a line which is parallel to the Y-axis, at X = 15 cm. The length of the line is unimportant. 3. Select Revolve from the 3D Features Toolbar. 4. Set Base Object to Sketch1 and Axis to the line which you have just drawn (which will be selected by default). 5. Set Direction to Reversed and Angle to 45 degrees. 6. Click on Generate to extrude the inlet pipe. Finally, you can extrude to make the straight section of the pipe. However, you need to extrude from the end surface of the pipe, which isn't currently defined as a sketch or plane, so first you need to construct the appropriate plane. 1. Create a new plane ( ). 2. Set Type to be From Face and Subtype to be Outline Plane. 77 CFX-Mesh Tutorials . . © SAS IP, Inc. Section 1: Geometry Creation [...]... will be called “Assembly 1” not “Assembly 2” as noted in the tutorial (since it was imported first) 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 CFX-Mesh Tutorials © SAS IP, Inc 79 80 Tutorial 8: Annulus This is a very simple example which shows how to mesh a two-dimensional geometry... Inflated Layers to 5 Set Maximum Thickness to 0.5 cm CFX-Mesh Tutorials © SAS IP, Inc Section 2: Mesh Generation 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 CatConvMesh.gtm The mesh is now complete 1 Select File>Save to save the CFX-Mesh database 2 Switch to the Project Page using... Layer Growth for Inflation, and • Extruded 2D meshing 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 NonNewton.wbdb 2 Choose New Geometry to open DesignModeler, specifying the unit of length to be Foot Creating... the Model View 4 Generate to create the plane Click on 5 Select 6 Extrude from the 3D Features Toolbar Set Base Object to be the plane that you have just created (Plane7) and Depth to 10 cm 7 Click on Generate to create the extrusion 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... Toolbox of the Sketching tab to create a circle centered on the origin with a radius of 0.5 ft 5 Use Circle again to create another circle centered on X = 0 ft, Y = 0.125 ft, with a radius of 0.75 ft CFX-Mesh Tutorials © SAS IP, Inc ... and choose File>Save to save the project If you want to continue by working through the CFX-5 example “Tutorial 10: Flow in a Catalytic Converter” 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 CatConvMesh.gtm... 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 In this case, two 2D Regions are required, one on the end of the pipe to allow an Inlet or Outlet Boundary Condition to be applied and a second on the end of the flange . 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. 69 CFX-Mesh Tutorials . . © SAS IP,. put the geometry into a good position for viewing the mesh. Tutorial 6: Butterfly Valve CFX-Mesh Tutorials . . © SAS IP, Inc. 68 Notice how the nodes are concentrated around the valve. Generating. 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. 79 CFX-Mesh Tutorials . . © SAS IP,