First, you need to understand an important distinction between 2D Regions and solid faces which applies when there is more than one Solid Body present in the model which is what we have
Trang 1Create a new sketch ( ) based on the ZXPlane
2 Use Line from the Draw Toolbox of the Sketching tab to create the line To position it, place the first
point at Z = 0 m, X = 0 m and then put the second point down at approximately the correct angle, as shown in the picture below
3 Now specify the exact angle as follows Use the Dimensions section of the Sketching tab, and choose
Angle Then click on the line and then on the X-axis If the wrong angle is displayed after you have selected
the axis, then right-click and choose Alternate Angle until the correct angle is displayed Click in the Model View to position the angle label Finally, type the angle, 6.06 degrees, into the Dimensions box
in the Details View
The Extrude operation can be used for this extrusion
1
Select Extrude from the 3D Features Toolbar.
2 Set Base Object to be Sketch1, and set Operation to Add Material.
3 Click on Direction Vector to change it from just being None (Normal) Right-click in the Tree View over Sketch3, and select Keep Visible, then click on the single line in Sketch3 which defines the direction vector Press Apply in the Details View The text should now read 2D Edge.
4
Set Depth to be 1.2 m and Merge Topology? to No Click on Generate to extrude the bottom
end of the coil
Extruding the Top End of the Coil
The actions above will be repeated to extrude the top part of the coil However, there is no existing sketch to use to extrude from Instead, you will create a new plane from the top circular end of the coil, which can be used for this purpose
1
Create a new plane ( )
2 Set Type to be From Face and Subtype to be Outline Plane.
3 Set Base Face to be the circular face at the top of the coil This can be selected directly by clicking on it
in the Model View
Trang 2Click on Generate to create the plane.
The Extrude operation can again be used for this extrusion
1
Select Extrude from the 3D Features Toolbar.
2 Set Base Object to be Plane4, and set Operation to Add Material.
3 Click on Direction Vector to change it from just being None (Normal) Click on the single line in Sketch3 which defines the direction vector, which is the same as for the previous Extrude Press Apply in the Details View The text should now read 2D Edge.
4
Set Direction to Reversed, Depth to 1.2 m, and Merge Topology? to No Click on Generate to
extrude the top end of the coil
Trimming the Ends of the Coil
Now trim the ends of the coil as follows
1 Create a new sketch based on the XYPlane
2 Use Circle from the Draw Toolbox of the Sketching tab to draw two circles in the new sketch Both should
be centered on the origin, and their radii should be exactly 1 m and at least 1.5 m respectively
3
Select Extrude from the 3D Features Toolbar.
4 Set Base Object to be the new sketch, and set Operation to Cut Material.
5
Set Depth to be 2 m, and click on Generate to remove the ends of the pipes.
Creation of the Container
You have already created the coil, and the next step is to create the container around the coil DesignModeler has an Enclosure feature which allows the easy creation of a cylindrical enclosure around a solid body and gen-erates the cylinder automatically; however, this only works if the solid body is not required to touch the edges
of the enclosure In this case, the ends of the coil will touch the sides of the container, so although the Enclosure feature can be used, you will have to construct the cylinder manually first
The first step is to freeze the coil, so that it is not affected by the next geometry creation actions, and to give it
a name, so that it can easily be identified later
Section 1: Geometry Creation
Trang 31 Select Tools>Freeze.
2 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 “Coil” Pressing Enter on the keyboard will let the name change take effect
3
Create a new sketch ( ) based on the XYPlane
4 Use Circle from the Draw Toolbox of the Sketching tab to draw two circles in the new sketch Both should
be centered on the origin, and their radii should be exactly 1 m and 0.5 m respectively Since a circle of radius of 1 m already exists in an earlier sketch, you may find that if you try to set the radius of the outer circle to be 1 m using the Dimensions Toolbox, you get a warning: “New dimension makes model over-constrained.” This occurs if DesignModeler has applied Auto Constraints to your new circle, already
constraining the radius to be 1 m to match the existing circle If you do see this warning, then click OK
to clear the warning and then right-click over the Model View and select Cancel You will not need to
set a dimension on this circle in this case
5
Select Extrude from the 3D Features Toolbar.
6 Set Base Object to be the new sketch, and set Operation to Add Material.
7
Set Depth to be 2.25 m, and click on Generate to create the container.
8 In the Tree View, under where it says “2 Parts, 2 Bodies”, click on Solid In the Details View, click on the
“Solid”, rename it to “Container” and then press Enter on the keyboard
The next step is to cut the coil out from the container, using the Enclosure feature
1 Select Tools>Enclosure from the Menu Toolbar.
2 Set Shape to User Defined.
3 Select the container as the User Defined Body To select it, you can click on Container in the Tree View,
under “2 Parts, 2 Bodies”
4 Set Merge Parts? to Yes This ensures that the final bodies are all in one part, and saves you from having
to merge them into one part explicitly later on The Merge Parts operation is able to operate more reliably
if the surfaces which form the interface between the two parts are not just closed loops, and this is the reason for breaking the circle in Sketch 1 into two separate pieces
5
Click on Generate to cut the coil out from the container.
This operation cuts a coil-shaped hole in the container, without deleting the coil, as required
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.
Trang 4Setting up the Regions
Create the 2D Regions:
1 Create a Composite 2D Region called inflow on the large annular face with the lowest Z-coordinate.
2 Create a Composite 2D Region called outflow on the large annular face with the highest Z-coordinate.
Finally, you need to create a Composite 2D Region on the coil itself First, you need to understand an important distinction between 2D Regions and solid faces which applies when there is more than one Solid Body present
in the model (which is what we have here: one solid is the coil, and the other is the container) Where two Solid Bodies meet at a common face, there is just one face present in the geometry; however, there are two 2D Regions,
as shown in the example below
If your model has only one solid, then there is no difference between a face and 2D Region If your model has more than one solid, then all of the external faces will also be 2D Regions However, two 2D Regions will exist for every internal (shared) face
So when you create the Composite 2D Region on the coil, you have to be very clear which side of the face you want to select to include in the 2D Region Since you are going to be applying Inflation to the 2D Region, you need to select the 2D Regions on the container side of the faces, so that the Inflation grows into the container (where you have fluid flow and need to resolve the boundary well) and not into the coil itself (where there is only heat transfer and no particular need to resolve the boundary fields)
To make the selection easier and to ensure that you only pick 2D Regions on the container side and not the coil side, you will first suppress the coil This ensures that only the container faces can be picked
1 Click on the plus sign next to Geometry in the Tree View to open it up Click on the plus sign next to
Part 3 to show that the Part contains two Bodies.
2 Click on the name of each Body in turn: this will highlight the appropriate Body in the Model View Note which Body corresponds to the coil and which corresponds to the container
3 Right-click on the Tree View entry for the coil Body in the Tree View, and select Suppress.
4 Right-click over Regions in the Tree View and select Insert>Composite 2D Region Change its name
to coil surface.
5 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 for the selection
6 In order to better see the inside of the coil, click on Geometry in the Tree View, and in the Details View, set Transparency to 40 %.
7 Click back on the new Composite 2D Region in the Tree View, and then select all six of the coil faces,
pressing Apply to finalise the selection These can be most easily selected by using Box Select (drag a
box across the Model View which encloses the whole of the coil but not the whole of the cylinder whilst holding down the left mouse button)
Section 2: Mesh Generation
Trang 5If you only appear to have five or four faces making up the coil surface, then go back to your
Design-Modeler tab and check that you set Merge Topology? to No for both of your Extrude operations If you
find that you did make a mistake in DesignModeler, then fix the problem in DesignModeler (making sure
that you press Generate to apply the changes) and then in CFX-Mesh, right-click over Geometry in the Tree View and select Update Geometry to update the CFX-Mesh session to use the corrected geometry.
8 In order to see clearly which 2D regions you have selected, right-click over Part 3 in the Tree View under Geometry, and select Suppress Now click on the new region name coil surface to see exactly which
faces it contains The regions selected should look like the picture below
9 Now right-click on Part 3 and choose Unsuppress Note that the coil Body is still suppressed If you were
to leave it suppressed, then it would not be included in the mesh
10 Right-click on the coil Body and select Unsuppress.
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 0.1 m, and press Enter on the keyboard to set this
value
1 Right-click on Spacing and select Insert>Face Spacing
2 In the Details View, set Face Spacing Type to Constant, and set the Constant Edge Length to 0.07 m.
3 Set the Radius of Influence to 0.0 m, and Expansion Factor to 1.2.
4 For Location, select the Composite 2D Region coil surface from the Tree View.
Note that the Composite 2D Region coil surface only contains one side of the coil faces, not both However, by
setting a Face Spacing on this region, you are implicitly controlling the face spacing on the both sides of the coil faces since the surface mesh on both sides of the faces must be identical
Proximity will greatly improve the mesh for this tutorial However, in order to keep the number of elements down
for tutorial purposes, the Number of Elements Across Gap is reduced from the recommended number 4 down
to 2
1 Click on Proximity in the Tree View.
2 Set Surface Proximity to Yes and change the Number of Elements Across Gap to 2.
Create an Inflated Boundary on the coil:
Trang 61 Click on Inflation in the Tree View In the Details View, set Number of Inflated Layers to 4.
2 Leave the rest of the parameters as their default values
3 In the Tree View, right-click on Inflation and select Insert>Inflated Boundary.
4 For Location, select coil surface from the Tree View.
5 Set Maximum Thickness to 0.1 m.
Because only one side of the faces which form the boundary between the coil and container are contained in
coil surface, Inflation will only take place on the container side of the faces.
Generating the Surface Mesh
You can visualise your inflation layer to see the effect of choosing only one side of the coil faces for Inflation
1 Right-click over Default Preview Group, and select Generate This Surface Mesh.
Your mesh should show that the inflated layers are all outside the coil You may see that the inflation layers do not go all the way round the coil ends; this is because the coil meets the container at a very shallow angle and the inflator cannot easily fill the very narrow gap
You may also find that the surface mesh generation process produces warnings about poor angles This indicates that the mesh is not of a high quality, and it is the result of meshing this geometry with over-coarse length scales (in order to keep the solution time down for tutorial purposes)
Now create another Inflated Boundary on the wall of the container:
1 In the Tree View, right-click on Inflation and select Insert>Inflated Boundary.
2 For Location, select the outside and inside walls of the container (the large cylindrical face and the inner
cylindrical face) from the Model View
3 Set Maximum Thickness to 0.1 m.
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 HeatingCoilMesh.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 14: Conjugate Heat Transfer in a Heating Coil” 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 HeatingCoilMesh.gtm to open up CFX-Pre.
2 Once CFX-Pre has opened, choose File>Save Simulation As to save the simulation as HeatingCoil.
Section 2: Mesh Generation
Trang 73 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.
Trang 8Tutorial 11: Airlift Reactor
This example creates the geometry and mesh for an airlift reactor or bubble column The two figures above show the geometry created in DesignModeler (left) and a schematic picture of the full geometry, not to scale (right)
In the CFD simulation, the air is input through a small ring sparger It then rises up to the top of the geometry and leaves the reactor A thin draft tube helps to stabilize the rising plume of bubbles The full geometry is rota-tionally symmetric, so only a 30-degree segment needs to be modeled
The draft tube will modeled as a “thin surface” (which has no thickness), and so it must be created as an internal face of a separate body, which will need to be created in DesignModeler The following geometry and meshing features are illustrated:
• multiple solid bodies;
• Imprint Surfaces, to add surfaces for boundary conditions; and
• Face Spacing, to refine the mesh on a particular face
If you want to skip the geometry creation part of the tutorial, then see the instructions in Introduction to the CFX-Mesh Tutorials
Trang 91 Geometry Creation
Creating the Project
1 Open ANSYS Workbench, and create a new empty project Save it as BubbleColumn.wbdb.
2 Choose New Geometry to open DesignModeler, specifying the units as centimeters.
Creating the Main Solid
The first step is to create the main solid
1
Create a new sketch ( ) based on the XYPlane
2 Use Polyline from the Draw Toolbox of the Sketching tab to create a closed polyline in the shape shown
below (the Y-axis is vertical) To close the polyline, right-click over the Model View after you have selected
the last point and select Closed End.
3 Use Circle from the Draw Toolbox to create the circle shown in the diagram.
4 Use the Dimensions Toolbox of the Sketching tab to add the dimension labels H1, H2, etc shown in the picture It does not matter if your labels do not have the same names as the ones in the picture You will
need to use the Horizontal, Vertical and Radius items from this Toolbox to label the “H”, “V” and “R”
dimensions, respectively
5 To ensure that the length of the bottom of the reactor is the same as the length of the top (H1), select
Equal Length from the Constraints Toolbox of the Sketching tab, and then select the top and bottom
edges of the sketch This ensures then when you set (or change) the dimension H1, both top and bottom
of the reactor are affected
6 Now use the table below to assign actual lengths to the dimensions listed in the Details View Since the original sketch is not to scale, you will find that the geometry changes shape as you apply each one, particularly when you specify the bubble column height
Length Dimension label in picture above
8.0 cm H1
Column radius
Trang 102.5 cm H2
Distance between draft tube and outside of column
3.0 cm H3
Distance between axis and sparger
77.0 cm V4
Height of column
3.5 cm V5
Distance between top of draft tube and column top
3.5 cm V6
Distance between bottom of draft tube and column base
3.5 cm V7
Height of sparger above column base
0.4 cm R8
Radius of sparger
Now you can use this sketch to create the solid body
1
Select Revolve from the 3D Features Toolbar.
2 Set the axis for the rotation by clicking on the Y-axis and then clicking on Apply in the Details View.
3 Leave Direction set to Normal and Angle set to 30 degrees.
4
Click on Generate to create the solid.
Breaking the Sparger Surface to form the Inlet
When the CFD simulation is run, the gas is injected through the top of the small circular hole, through a 74-degree segment Currently, the hole is defined with just one surface, so this must be broken to allow the boundary conditions to be appropriately defined The steps below explain how to modify the solid to achieve this All of this could have been done as part of the original construction of the solid, but this tutorial has split the steps up
to make it clear exactly what each step achieves
1 The display will be clearer for the next step if you hide the solid for now: double-click on 1 Part, 1 Body
in the Tree View, right-click on Solid, and choose to Hide Body.
2 Select Sketch1 from the Tree View and go to the Modify Toolbox of the Sketching tab.
3 Click on Split, and break the circle into two parts by clicking on it in approximately the positions shown
below in the picture below The exact position of the breaks does not matter for the moment, but make sure that you don't choose break points which are exactly at the highest or widest points of the circle
Simply breaking the circle into two parts and regenerating the solid isn't enough to make the hole have two
surfaces This is because by default, the Revolve operation is set to use Merge Topology? as Yes This has the
effect of optimizing the topology of the resulting solid, which in this case means that the hole is always created
as just one surface
1 Select the Revolve1 object from the Tree View.
Section 1: Geometry Creation