Workshop 8.3 3D Pipe Junction O-grid

3D Pipe Junction - Ogrid
3D Pipe Junction - Ogrid
In this workshop, we will open the geometry and blocking from the previous workshop, 7.3 3D Pipe Junction, and continue with it
Check quality to show bad elements
Create an Ogrid which will greatly improve the quality
Rescale Ogrid
Convert mesh to unstructured
Write mesh to CFX

Open Project
File > Open Project…
If you feel confident you made the blocking correctly with the previous project, 7.3, 3D Pipe Junction, then open that project
Otherwise, open the project provided, 3dpipe_before_ogrid.prj in 3DPipeJunct folder
This will open the geometry and blocking
Or use the utility icon to open project

Compute Pre-Mesh
Right click on Blocking > Pre-Mesh > Recompute
This will compute the pre-mesh without turning the mesh display on
It can also be used to force a compute of the mesh at any time when turning on Pre-Mesh does not recognize a change done in any particular blocking operation

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Quality Check
Blocking > Pre-Mesh Quality Histograms
Set the Criterion to Determinant 2x2x2
Apply
A good mesh should have little or no elements below the 0.2 – 0.3 range, so select the elements below this and inspect
Change criterion to Angle
Apply
A good mesh should have no elements below 18 degrees, so select the elements below this and inspect
Right click in histogram to turn off Solid, Show, or Replot with different axes
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Done will close histogram
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Surface Mesh Display
The problem mesh is easily seen by looking at just the surface mesh on the INLET surface
Turn off all parts except FLUID_MATL (contains the blocks) and INLET
Turn on Pre-mesh
Turn off Edges
Right click to turn on Pre-Mesh > Solid & Wire
This occurs in the block corners because the edges project to the curves, and the curve meets tangently at these block corners

Create Ogrid
First, turn ON Edges and all parts (except VORFN), and turn OFF Pre-Mesh
Blocking > Split Block > Ogrid Block
Press the Select block(s) button, and select all the blocks (can box select or press ‘v’)
Press the Select face(s) button, and select the faces on the SYMM, INLET, and OUTLET surfaces as shown
Apply
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Rescale Ogrid
Rescaling Ogrid is one of the commands that can work on only visible vertices
Right click on Blocking > Index Control in model tree
Set I from 2 to 3 by using the arrows
Blocking > Edit Block > Modify Ogrid
Method set to Rescale Ogrid
Press Select edge(s) button
Select any of the small “radial” edges
Enter 0.6 for the Offset
Apply, then press Reset in the Index Control
Every visible edge of the Ogrid will be 0.6 of its original length
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Update Sizes
Any new edges have 2 nodes by default
Blocking > Pre-Mesh Params > Update Sizes
Transfers surface and curves sizes to edges
Apply
You will need to redo the Scale Sizes by 1.5
Only 2 nodes on the new edges
After Update Sizes
After Scale Sizes by 1.5
Turn on Pre-Mesh
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Set Edge Parameters for Boundary Layer
Blocking > Pre-Mesh Params > Edge Params
Do NOT Update Sizes after setting Edge Parameters, or it will destroy any work you did setting sizes and distributions on edges
Select any of the radial edges of the Ogrid
Set Spacing 1 to 0.1 and Ratio 1 to 1.3
Increase the nodes until Ratio 1 in the actual column gets near the requested Ratio 1, about 14 nodes
Enable Copy Parameters and Apply
Recompute pre-mesh (turn Pre-Mesh OFF then ON)
Actual column
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Recheck Quality
Check determinant and angle again
Blocking > Pre-mesh Quality Histograms
Check Determinant 2x2x2 then Angle
Highlight Angles above and below 18 degrees
Turn off Pre-Mesh to see where they are at
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Move Vertex
Blocking > Move Vertex > Move Vertex
With the Method set to Single, press the Select vert(s) button and drag the 2 vertices as shown
You’ll also want to drag the nearby 2 internal vertices in the same fashion
Turn Pre-mesh ON
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Quality compare
Initial Determinant
Improved Determinant
Initial Angle
Improved Angle
After Ogrid Creation
Before Ogrid Creation
RE-check Determinant and Angle
Mesh quality is greatly improved after Ogrid
Minimum determinant should be around 0.2 or 0.3.
It is well over this.
Minimum angle should be 18 degrees. It is decently over this too.