Workshop 1:
Basic Skills
14.5 Release
Introduction to ANSYS
Fluent Meshing
© 2011 ANSYS, Inc.
December 21, 2012
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Release 14.0
I
Introduction
Workshop Description:
This workshop shows some of the clean up tools in Tgrid for boundary meshes.
Learning Aims:
You are going to use the tools to clean up the given surface mesh and generate a
volume mesh.
This workshop will cover how to
– Create and display groups
– Visualize problem areas
– Use global and local tools for cleaning up the mesh
– Using text commands
– Checking quality of mesh
– Improving quality using global and local tools
– Using hot keys
– Troubleshooting techniques
– Generating mesh and improving its quality
– Setting zones and boundary conditions
© 2011 ANSYS, Inc.
December 21, 2012
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Release 14.0
Starting ANSYS Fluent in Meshing Mode
– Open the Fluent Launcher by clicking the Windows Start menu, then selecting Fluent.
14.5 in the Fluid Dynamics sub-menu of the ANSYS 14.5 program group.
– Enable Meshing Mode under Options.
– Set Working Directory to the area where files are
– Click OK to start Fluent in meshing mode.
© 2011 ANSYS, Inc.
December 21, 2012
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Read and display the mesh
File  Read  Mesh...
• Select the mesh file WS1_asmoNS-for-repair.msh.gz and click
Open.
• Display the mesh Display 
Grid... opens the Display Grid
panel
In the Faces tab, select all the items
under Face Zones using the
Boundary filter and click Display.
As you rotate the geometry you
can see the edges of the model as
wireframe rotation is activated. It is
a car in a wind tunnel.
© 2011 ANSYS, Inc.
December 21, 2012
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Displaying Different Zones
In the Face Zones list all the car zones have the prefix
car-* and all the wind tunnel zones have the prefix
wt-*. This will help to switch the visibility on and off
between the two areas. So you can select all the car-*
zones and display the car .
Or you can select all the wt-* zones to display only the wind tunnel.
© 2011 ANSYS, Inc.
December 21, 2012
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Creating and Displaying Groups
To make things easier you can create two groups, one for
car Face Zones and another for wind tunnel Face Zones
• You can use the Selection Helper... option under
Display menu to aid selection of multiple boundaries
Display  Selection Helper...
• Enter the wild card option car* or wt* for Zone Name
Pattern and click Select to select all the zones with that
prefix.
• Use the Groups... key inside the Create group box.
• Click Groups....
– Use the Zone Selection Helper to select all the
zones starting with car-* in the list under Face
Zones in the User Defined Groups dialog box
and click Create.
– Enter _car for Name in the Group Name
dialog box and click OK.
– Similarly create a group _wt for the wind
tunnel zones.
© 2011 ANSYS, Inc.
December 21, 2012
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Visualization of Problem Areas
You are going to use the visualization tools inside Fluent meshing to see where the
issues are with the surface mesh.
• Enable Free under Options and
display all the zones through the
Display Grid dialog box.
The zones marked in blue are the
free faces which you have to fix.
• Disable All from the Options list to easily
check for the problem areas.
There are various global and local tools inside
Fluent Meshing which can be used to fix such
connectivity issues.
© 2011 ANSYS, Inc.
December 21, 2012
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Merge Nodes
Open Boundary  Merge Nodes...
This option will merge the nodes within a specific
tolerance.
• Enable the option of Percent of shortest
connected edge length (recommended for CFD
quality surface meshes)
• Retain the default value of 10%
• Click Merge.
• The Message displays the number of boundary
nodes and faces merged.
• Click Display in the Display Grid
dialog box to redisplay the free nodes.
You can observe that the number of free
nodes has reduced considerably. All the
ones on the wind tunnel boundary are
fixed.
© 2011 ANSYS, Inc.
December 21, 2012
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Merge Nodes with Increased Tolerance
If you zoom in you can observe that some of the
nodes with bigger tolerance difference will not be
affected. They require more than 10 % tolerance to
be merged. You will increase the tolerance in steps
of 10 till you reach 50 % and observe the change.
• Select all the Boundary Face Zones in the
Compare... group box and increase
Tolerance by 10.
• Merge and redisplay.
• Ensure all boundaries are selected in
each list
• Repeat for 20%, 30%, 40% and 50%
Write the mesh
File Write Mesh
nodesmerged.msh.gz
Each step improves the connectivity of the
mesh, reducing the number of free faces.
© 2011 ANSYS, Inc.
December 21, 2012
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Release 14.0
Faceted Stitch
Nodal mismatches can be too big for Node
Merge to deal with. You can instead use a
global tool of Faceted stitch for large
tolerance node merging. We advise
saving the mesh before this is used as it
can destroy geometry if used incorrectly.
Always Merge Nodes first.
Boundary  Mesh  Faceted Stitch
• In the Faceted Stitch dialog box
select all the zones under Tri
Boundary Zones.
• Enter a low value for the
Tolerance = 0.01.
• Click Stitch.
• Observe that this fixes most of
the free faces.
• We will now fix the remaining
issues with local, manual
methods.
© 2011 ANSYS, Inc.
December 21, 2012
Faceted Stitch
Write the mesh
File Write Mesh
stitched.msh.gz
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Clean Up “Multi” Connected Faces
•
In Display  Grid deselect All
Face Zones and check only
Multi for options
•
Hit Display
•
Use ctrl-a hotkey to autoscale
the view
•
Switch to Face Filter by using
hotkey ctrl-f and select face as
shown which will populate
“Selection” in the Bounds
tool
•
Select delta of 150 and click
Set Ranges. Note this is linked
to Bounds in Display Grid.
•
Click Display in Display Grid • The “hanging” face seen is not required. Select it
and ctrl-a to autoscale
with ctrl-f and then Ctrl-w deletes or you can use
© 2011 ANSYS, Inc.
December 21, 2012
Release
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Boundary
 Modify to select the face and
Delete
Fixing Final Free Faces
•
In Display  Grid select all
boundaries, check Free and Display
•
There are a number of Free faces
and some groups stand out as being
indicative of holes – see red rings
•
We will zoom on each of these holes
to close them
•
Remember, middle mouse click
centres the view on a point and
then you can rotate or zoom on that
point easily
•
Read the next two slides to see how
this can be done with Boundary 
Modify
© 2011 ANSYS, Inc.
December 21, 2012
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Using Node Filter to Fix the Holes
Now you will try to fix the holes.
•In the Display Grid dialog box select the group _car from the Face Zone Groups.
•Enable All and Free from the Options list.
As you can see it has some missing facets. You can use the Modify Boundary dialog box to fix the
holes.
• Select node from the list under Filter.
• Select 3 nodes as shown and click
Create operation to create triangles.
•Another option is to select Edge filter
and click Create. It will to fill a
structure from any free edge loop.
Hot Key for Deselect Last is
Escape
This will fix the hole above. You can use similar methods to fix the rest of the holes.
© 2011 ANSYS, Inc.
December 21, 2012
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Repair Holes Hotkey
•
Instead of selecting the hole edges
manually we can use a “repair zones”
hotkey to fill multiple holes at once
•
Select some random faces using face
filter in your model (ctrl-f)
•
Delete these faces with the delete
hotkey (ctrl-w)
•
Switch to zone filter (ctrl-z) and pick the
zone(s) you have created holes in (carmain-body in the example)
•
Use ctrl-r hotkey to fill the holes you
created
© 2011 ANSYS, Inc.
December 21, 2012
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Local Clean Up Tools[1]
We will use some of the operations in Modify
Boundary to clean up the final issues with the
mesh.
• Boundary  Modify...
• In the Modify Boundary panel select
node from the list under Filter.
• Select the master node and a slave node
to merge with and click Merge. This will
fix the problem there.
• Note the master’s position is kept so if
near a feature the node on a feature
should be chosen first. Collapse would
merge the two to the mid-point instead.
• Similarly fix the other free
nodes In the geometry.
© 2011 ANSYS, Inc.
December 21, 2012
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2. Slave
1. Master
Hot Key for Node Merge is F9
Release 14.0
Local Clean Up Tools[2]
• Sometimes you reach a stage as
shown in the figure where there is no
node pair to merge.
• Switch to Edge Filter, select the edge
as shown and click Split to split the
edge. Select node Filter and select
the two nodes to merge. The two
nodes are at virtually the same
location. Always click into the corner
of the tri nearest the node you wish
to select rather than trying to directly
click the node position itself.
• Click Merge to fix.
This is to demonstrate some of the local
operations. Local operations should be
minimized as much as possible. You
should try to fix most problems using the
global operations.
© 2011 ANSYS, Inc.
December 21, 2012
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Verify Connectivity
•
Once there are no Free or Multi faces we can verify
connectivity and move on to worry about the quality of the
surface mesh
•
Ensure that you have bounds reset and check one last time
for Free and Multi faces
•
Use ctrl-a hotkey to autoscale the view to the screen
•
Fix any remaining issues
© 2011 ANSYS, Inc.
December 21, 2012
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Fixing Poor Features
•
•
•
•
•
•
•
•
Here we fix a kink in the roof
Zoom on the area highlighted
Open Boundary  Modify
Switch to Node Filter
Select two nodes as shown
Click Set
Choose node to move
Click Project
© 2011 ANSYS, Inc.
December 21, 2012
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Rezoning Triangles
• In Display Grid choose only the car-front boundary and
hit Display
• You can see that the feature edge is not smooth and
some triangles should belong to car-main-body
• Open Boundary  Modify and using face Filter, select
the faces required to rezone into car-main-body (hint:
rotate shows them clearly by their edges)
• Switch to Zone Filter and select the car-main-body in the
graphics window with RMB or type car-main-body into
the “Enter Selection” window and press <Enter> to add
to Selections list
• Click Rezone Operation to move the faces
© 2011 ANSYS, Inc.
December 21, 2012
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Checking Quality[1]
• To check the quality
Report  Face Limits...
• Select all the zones under Face Zones. Click Compute.
You can see that there are some highly skewed elements. We will aim to
bring the Maximum value below ‘0.7’ before creating a volume mesh.
• You can also plot the histogram of quality.
Display  Plot  Face Distribution...
• Select all the zones under Boundary Zones.
• Click Plot.
You can see that most of the faces are of very
good quality. If you change the Minimum and
Maximum values you can concentrate on the
high skewness end. You can see that there are
elements with skew > 0.8.
some
© 2011 ANSYS, Inc.
December 21, 2012
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Checking Quality[2]
• If you change the number of Partitions to 1 in
Face Distribution dialog box, you can observe
the number of elements above 0.8 Skew. If
you click Print the info is printed to the
console.
You need to fix these poor quality faces before
going ahead with the volume mesh. We will
go further and aim for skew < 0.7.
• To display the skewed elements enter 0.7 for
Minimum in the Face Quality Range group
box in the Display Grid dialog box.
• Enable Quality in the Options group box.
• Select _car In the Face Zone Groups list.
• Click Display to check the low quality area.
• Disable All and click Display to see where the
elements are in the model.
• Zoom to a bad element then enable all and
redisplay to see the context
© 2011 ANSYS, Inc.
December 21, 2012
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Some skewed elements
Release 14.0
Improving Quality (Use Global Method)
Boundary  Mesh  Improve…
• In the Boundary Improve dialog box,
select all the zones under
Tri Boundary Zones.
• Ensure that the Quality Limit is set to
0.7. Click Apply.
You can see from the message printed in
the console that you started out with a
quality of 0.98 and after a few iterations
that quality has been improved
considerably.
Display the skewed faces to check if the
quality there is improved. As you can see
the boundary improve command has
stretched out the triangles by node
smoothing smoothing. There is still a tiny
cell remaining which is shown in
‘red’.
© 2011 ANSYS, Inc.
December 21, 2012
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Release 14.0
Improving Quality
Some faces may not have improved because
the settings in the Boundary Improve dialog
box constrain the improvement algorithm to
avoid distortion of any feature/patch edges.
•If the skewed elements are around a feature,
you need to be a little more delicate to preserve
the feature. You can move the nodes with the
Move To Operation.
• In Boundary  Modify hit First to zoom
on the worst skewed face
• Switch to node Filter and select the
node you will move
• Select position Filter.
• Right-click to select the position where
you would like to move the node to.
• Click Move To
• If the operation is successful the face
should no longer be highlighted red
• Click Next to proceed to next worst face
© 2011 ANSYS, Inc.
December 21, 2012
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Position
Node
Release 14.0
Hot Keys
If you click in the graphics window and press
‘Ctrl+h’ you can get the list of hot keys printed
on the console. You can use these hot keys to
speed up cleanup operations considerably.
When you execute the hotkeys, you can see that
it prints in the console the equivalent textinterface command you would use for the
hotkeys.
• After cleaning up some of the faces using the
Boundary Modify panel, check the quality again
Report  Face Limits...
• Select all the zones under Face Zones.
• Click Compute.
© 2011 ANSYS, Inc.
December 21, 2012
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Troubleshooting [1]
When the Maximum skewness is computed below 0.7 then you can generate a Tet mesh.
Mesh  Tet...
• You can retain all the
default settings and
click Init&Refine in the Tet dialog box.
You should get an error informing that an edge is intersecting a face.
If you click OK, you will be informed that mesh init and refine is not
completed.
• Click Cells tab in the Display Grid dialog box.
• You can see that a dead cell zone is created since
refinement was not completed.
© 2011 ANSYS, Inc.
December 21, 2012
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Troubleshooting [2]
In the Faces tab you can see that a virtual-face is
created. If you display this face we see the tet init
mesh is exploding out to some bounding box.
Clear the mesh so that the cell zones (dead) and virtualface are removed.
• Mesh  Clear
Use the error message in the console window to locate
the problematic area.
• Copy the face ID from the console and paste it to the
Selection area in the Bounds group box on the task
page, set +/- Delta to 5 and click Set Ranges.
• Click Display in the Display Grid dialog box.
• You can increase/decrease the display bounds by
clicking the up/down arrow key.
You can see a node projecting through a surface, which
confirms that an edge is intersecting a face.
© 2011 ANSYS, Inc.
December 21, 2012
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Increase
bounds
Release 14.0
Troubleshooting [2]
You could have found out this before initializing the mesh by
using a text command.
• Press ‘Enter’ to see the list of commands.
• Mark intersecting faces using
• /meshing/boundary/mark-face-intersection
• Enter ‘*’ to select all when prompted to enter Boundary
Face Zones, as shown
• Press ‘Enter’ for the remaining prompts.
You get a message in the console that 11 faces are marked.
• To display marked faces, you can disable everything in the
Display Grid panel under Options, highlight all Face Zones
in the list and then click Display.
Ensure that you have Reset the bounds.
All the 11 marked faces are displayed. These require fixing.
© 2011 ANSYS, Inc.
December 21, 2012
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Fixing Face Intersection
To fix the face intersection you can
select the faces and delete them or
smooth the apex node
• Switch to face Filter
in the Modify Boundary dialog box and
select the five faces shown
• Click Delete to remove the faces
Click Yes in the Question dialog box that
appears for confirmation of deletion.
You can see that a hole is formed in the face.
You can select Free from the Options
list and display the hole with the free nodes.
• To fix the hole select one edge of the
hole in the Modify Boundary dialog
box by selecting the edge Filter.
• Click Create.
If marked faces are still left. You
can use the /bo/clear-marked-faces TUI
command to remove the marks
© 2011 ANSYS, Inc.
December 21, 2012
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Generate Tet Mesh
You can now again try generating the Tet mesh
• Retain all the default settings and click Init&Refine in the Mesh  Tet dialog box.
After you have the Tet mesh you can see from the report
generated in the console that there are still some skewed
elements.
• In Display  Grid
• In the Cells tab select the zone under Cell Zones.
• Under Options disable everything other than Quality
• Set Minimum to 0.9 to view skewed cells over this value
• Click Display
• In the Faces tab highlight the _car group and Display
The skewed elements that are above the limit are displayed. The
cells seem to be centered around the area of the wheel ground.
To look at that in more detail you can check by looking at the cut
plane through the wheels as described next.
© 2011 ANSYS, Inc.
December 21, 2012
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Generate Cut Plane
To view the cut plane through the wheels:
• Zoom in on the elements.
• Select position Filter in Modify Boundary
dialog box, (or use ‘ctrl-x’ hot key), and
right-click to select a position at the center of
the element group as shown.
Since you want to look at a cut plane in Y direction, you extract the Y
coordinates from the dialog box or the message printed in the console.
• In the Bounds tab of Display Grid dialog box enable Limit by Y
and paste the Y coordinates for Minimum and Maximum.
This will limit it to a plane in that coordinate direction.
• In the Cells tab enable All and click Display.
You can see the problem areas down in the corners where there are sharp angles.
Zoom In
© 2011 ANSYS, Inc.
December 21, 2012
Zoom In
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Using Auto Node Tool
To fix the skewed cells we can:
• Clear the mesh and repair the boundary or
• Do local smoothing using the Auto Node Move tool
This will move the local nodes to improve quality. We will
select boundaries to allow movement but we will restrict
movement along the surfaces to avoid changes to the
geometry
Mesh  Tools  Auto Node Move…
• Select all the Boundary Zones.
• Retain the default settings and click Apply.
A message will be printed in the console about
improved quality. Click Apply for few more iterations
and the quality will improve. Once it is brought to an
acceptable level the mesh is ready for the solver.
Dropping Dihedral Angle and deselection of “restrict
boundary nodes along surface” will allow more aggressive
improvements and better quality but risks loss of features
© 2011 ANSYS, Inc.
December 21, 2012
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Cell Zones and Boundary Conditions
• Mesh  Manage…
In the Manage Cell Zones dialog box you can rename the cell zone by
giving it a proper name. There could be multiple cell zones
• Select the Cell Zone.
• Select Rename from the list of Options.
• Enter the name “main-fluid” under Name and click Apply.
• List will print info on the cell zone to console
• Boundary  Manage…
In the Manage Face Zones dialog box you can change the face zones to a
boundary condition type.
• Select wt-inlet (wind tunnel inlet) from Face Zones.
• Ensure that Change Type is selected from the Options list.
• Select velocity-inlet from the Type drop-down list.
• Click Apply.
• Similarly set wt-outlet to pressure-outlet type, and wtsymmetry to symmetry type
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Mesh Ready
• Open Boundary  Manage
• Select all the Face Zones
• Click List to see the summary of all the
boundary condition types. The details will
be printed in the console. You can select
the Face Zone Groups and list the summary
for each group.
Now write the volume mesh.
File  Write  Mesh…
• Enter a proper name for the mesh and
click OK.
• Optionally, switch to Fluent solution
mode and continue to solve
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