1. Chapter 5.1 Mesh Preparation and Output to Solver
ICEM CFD Introductory Course

2. Edit Mesh
Usage of Edit Mesh tools
To diagnose and fix any problems and improve mesh quality
To convert element types
Refine and/or coarsen mesh
Manual and automatic tools
For imported as well as internally created mesh

3. Mesh Checks To diagnose mesh associativity problems
Errors – most likely to cause problems in:
Solver translation
Solver input
Solution convergence/run
Possible Problems – “Unclean surface mesh”
Unwanted elements
Unwanted holes/gaps
May result in incorrect solution
Can check any combination of errors/possible problems at any one time
Individually select
Click on Error or Possible Problems tabs will select all options in column – selecting again will de-select all
Set Defaults will select most commonly seen/detrimental diagnostics
Check Mode
Create Subsets – creates a subset of elements that fit each criteria
Check/Fix Each – offers automatic fixing of indicated problem

4. Mesh Checks: Mesh Errors
Duplicate Elements
Elements that share all nodes with other elements of the same type
Uncovered Faces
Volumetric element faces that are neither attached to the face of another volumetric element nor to a surface element (boundary face)
Missing Internal Faces
Volumetric elements that are adjacent to another of a different part with no surface element between them
Periodic Problems
Inconsistency in the number of nodes/faces between periodic sides
Special check for rotating (sector) or translational periodic grids
Volume Orientation
Left handed elements due to incorrect connectivity (node numbering of cell)
Surface Orientations
Volume elements that share the same surface element (overlap)
Hanging Elements
Line (bar) elements with a free node (node not shared by another bar)
Penetrating Elements
Surface element(s) that intersect or penetrate through other surface elements
Disconnected Bar Elements
Bar elements where both nodes are unattached to other bars

5. Mesh Checks: Possible Problems
Multiple Edges
Surface elements with an edge that shares three or more elements
Can include legitimate T-junctions
Triangle Boxes
Groups of 4 triangles that form a tetrahedron with no actual volume element inside
2 -Single Edges
Surface element with 2 free edges (not shared by another surface element)
Single-Multiple Edges
Surface element with both free and multiple edges
Stand-Alone Surface Mesh
Surface elements that don't share a face with a volumetric element
Single Edges
Surface elements with a free edge
Can include legitimate hanging baffles
Delaunay Violation
Tri elements with nodes that are within the circumsphere of adjacent elements
legacy quality criteria
Overlapping Elements
Continuous set of surface elements that occupy the same surface area (surface mesh that folds on to itself)
Non-manifold vertices
Vertices whose adjacent elements’ outer edges don't form a closed loop
Typically found in tent-like structures where surface elements jump from one surface to another across a narrow gap or sharp angle
Unconnected Vertices
Vertices that are not connected to any elements
Usually eliminated automatically upon saving the mesh

6. Mesh Checks If Create Subsets was selected
Will go through all checked criteria at once
Elements that have a particular error/problem are put into a subset with that diagnostic type name
Subsets activated in Model Tree
Turn off all parts or shells to view subsets
If Check/Fix Each was selected
Will be prompted with options one criteria at a time
Fix: Automatically fix the error/problem
Recommended only for Duplicate Elements, Volume Orientations, Periodic Problems, Overlapping Elements
Create Subset
Ignore
For example, multiple edges may be legitimate t-junctions; single edges – legitimate free edges

7. Mesh Smoothing Automatically improve element quality User chooses:
All element types
Necessary to have geometry loaded
Nodes are moved to improve the element quality
Automatic node movement constrained by node projection type to geometry type – e.g. curve nodes will be constrained to move only on curves
Histogram is automatically displayed/updated after smoothing
User chooses:
Criterion
Smooth Mesh Type
Smooth: Element types actively smoothed; quality of type appears as part of histogram.
Freeze: Nodes are held in place during the smoothing process; elements not in histogram
Float: Nodes can be moved along with adjacent smoothed elements, but quality ignored; not shown in histogram
Example: Freeze Prisms and Pyramids while smoothing Tetra. Float surface elements

8. Mesh Smoothing Advanced Options Smooth Parts/Subsets Laplace smoothing
Smooth all parts, visible parts (activated in model tree), or visible subsets
Quick, local smoothing
Laplace smoothing
Gives more uniform mesh size relative to neighboring elements
Recommended for TRI only – smooth Tetra after with Laplace turned off
Recommended prior to prism generation
Not just worst 1%
Factors in all elements instead of only the worst 1% of those beneath quality value and their neighbors
Violate geometry
Unconstrain nodes slightly from geometry within user defined tolerance – absolute or relative to minimum edge length of mesh elements

9. Output
ANSYS ICEMCFD Allows you to write input files for many CFD and FEA solvers. The output tab can be used to,
Select solvers
Define boundary conditions
Edit parameters
Write input file

10. Wing Edit Workshop File > Change Working Dir…
Choose WingEdit OK
Use the quick icon to open geometry
Choose WingEdit.tin
Open

11. Compute Mesh Select Mesh > Compute Mesh > Volume Mesh
Set Mesh Method > Robust (Octree) (default)
Compute

12. Quality histogram after smoothing
Mesh Smoothing
Mesh Smoothing
Edit Mesh > Smooth Mesh Globally
Specify 5 Smoothing iterations
Up to quality 0.4
Use other defaults
Apply
Right-click in quality histogram and select Replot to modify its display as shown
Quality histogram after smoothing

13. Reviewing the mesh Quality Histogram
Left-click on the columns up to 0.3 in the histogram to select the elements within those ranges
Hide Shells from the tree to make the elements easier to find
Review curves, and points to determine root cause
Extra curves and points in the geometry added additional constraints

14. Create/Modify subset Using a Subset
With the bars up to 0.3 selected, right-click in the histogram and select Subset
The elements are placed into a diagnostic subset called Aspect ratio (or selected criteria during smoothing) under the Mesh branch
Right-click on the subset name and select Modify
Select Add Layer(s) to Subset
Add 2 layers with Also volume elements turned off
This adds additional elements for ease in seeing surroundings
Select Remove from Subset by Selection
Click on Select all volume elements from the selection Select mesh elements toolbar
To only visualize and edit surface elements
Very difficult to view and edit volumes and usually not necessary

15. Merge Nodes Merging Nodes
Edit Mesh > Merge Nodes > Merge Interactive
Activate Ignore projection to allow removed node to un-project
With the subset displayed, turn off Shells from the tree
Right-click on Mesh and select Dot Nodes
Select 2 nodes from the screen – the first node is kept, the second is removed
Continue for length of problem are (~8 or 9 locations)

16. After merging and smoothing
Mesh Smoothing
Mesh Smoothing
Always smooth after manual editing
Edit Mesh > Smooth Mesh Globally
Use previous settings
Apply
Verify that lowest quality elements are removed from tail area
Right-click on the subset name “Quality” from the model tree and select Clear
Manual node movement is also possible using Edit Mesh > Move Nodes > Interactive
Preserves projection to geometry types
Remember to smooth again….
Before merging
After merging and smoothing

17. Check Mesh Checking the Mesh Select Edit Mesh > Check Mesh
Use the default set of checks and Apply
For Duplicate elements select Fix
These are duplicate line elements from the node merging process
For Hanging elements select Fix
These are Node elements no longer connected after re-meshing the subset
For Unconnected vertices select Delete
These are normally deleted during the Save process

18. Select Solver Select Solver Select Output -> Select Solver
Select Fluent_V6 as output solver
Apply

19. Define Boundary Conditions
Select Output -> Boundary Conditions
Expand Volumes
Parts that have volume cells are listed here
Expand the part LIVE
Click on Create New
Select the appropriate boundary condition (fluid) from the pop up window
Click OK
Similarly Expand Surfaces to see the parts that have the shell mesh. These parts could make up the walls, inlet, outlet etc. Expand the parts and define the appropriate boundary conditions
Click Accept

20. Write Input Write input file Select Output -> Write input
When prompted, save the project as WingEdit.prj
When prompted, open WingEdit.uns mesh file
The Fluent_V6 panel pops up
The output file will be saved in the working directory. The default name of the file is fluent.msh. The file name and location can be changed by typing it in the Output file filed
Click Done.
Fluent.msh file is created in the working directory