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[ICEM] ICEM meshing - Tips from forum - Collection

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Old   June 16, 2015, 09:47
Default ICEM meshing - Tips from forum - Collection
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M Sereez
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Dear ICEM Users;

What I am posting here is not my information. It is general guidelines, tips and Tricks I found on this forum. I am posting this because a lot of people ask the same questions again and again. Hope every one finds this helpful;

GENERAL PROCEDURE FOR OCTREE MESHING WITH PRISMS AND DELUNAY DEVELOPMENT BY A USER

1.0 Octree Volume mesh, to give me a watertight volume.
2.0 Delete the volume mesh.
3.0 Smooth & manually improve the surface mesh (Quality >0.5).
4.0 Then do a Delauney volume fill with advancing front option.
5.0 Smooth that volume mesh to obtain a quality above 0.3.
6.0 Grow 8 prism layers with an expansion ratio of 1.25, but no initial height set to allow the prisms to float.
7.0 Split the prisms in 3 to produce 24 layers, redistribute to give desired initial wall height.
8.0 Smooth tetras freezing pentas & any pyramids produced.
9.0 smooth everything up to around 0.05.

RULE OF THUMB GEOMETRY BUILD TOPOLOGY
1/10 th of minimum curve length in geometry

METHOD FOLLOWED BY FAR TO GENERATE TRI- TETRA PRISM MESHING OF A WING BODY
1) Set the Global element sizes.
2) Set Global surface mesh set up all tri patch dependent respect line elements to the smallest mesh length
3) Specify surface mesh settings individually for all surfaces. Specify curve elements use dynamic to control meshing parameters in the wing. bunching ratios.
4) Generate shell mesh tri elements.
5) Repair and improve surface mesh
6) Generate prism on top of surface mesh
7) Generate delunay volume mesh
8) Smooth all mesh in 2 steps

SURFACE MESHING OF A WING
Problem: problem is like that when i draw the patch independent surface mesh on the delta shape surface mesh penetrates the surface and it creates the problem when i draw the volume mesh
Simon replied:
Yes, we understand the problem...

We are telling you that there are several ways to fix it.

1) Setup "Thin Cuts"

2) Refine your mesh

3) Adjust "Edge Criterion"

ABOUT PRISMS FLOATING
There's two parameters in ICEM which deals with how prism layers are built and treated in relation to the prism-to-tetra transition: Max Height Over Base (MHOB) and Prism Height Limit Factor (PHLF). It seems to me from reading the material and trying different meshes (so I know what they do) that the MHOB is only suitable to cap the layering of prisms if they are not floated, and instead all required layers are build one after another. Whereas, the PHLF is only suitable when floating the prisms to give a smooth prims-to-tetra transition.
(answered by simon)
Floating the prisms is similar to using PHLF, except that you don't set the initial height (it gets calculated).

You can't really use MHOB and PHLF at the same time. Which ever ratio it hits first will prevent the other one from being reached.


HOW TO MERGE 2 MESHES AT SYMMETRY (SIMON)
Are you mirroring the blocking or just the mesh? If it is topologically symmetrical, but not geometrically symmetrical, you should mirror the blocking and then adjust to fit the actual geometry... But if it is geometrically symmetrical, you can just mirror the mesh, then merge nodes with a tolerance and delete the symmetry shells.

ABOUT FAR FIELD (FAR)
Oh, I check the domain extents and they are too close to the body. Body length is approx. 1000 units and downstream is 5000 units (5 lengths) and upstream boundary is 2000 units (2 lengths). And the flow is low subsonic. For this you need at least 10-15 lengths upstream and 20-30 lengths downstream. Similarly 10-15 lengths in Y and Z direction

ABOUT WALL DISTANCE ( FAR)
Wall distance is the another measure of aspect ratio. It is required by SA and two equation omega based models. You should avoid the high aspect ratio at the far field. Higher aspect ratios are allowed (upto 1000 for dp), but I have also tested the aspect ratios up to 8000-10000 for NASA rotor 37 and results were still comparable to experiments with 2-3% error.

So rule of thumb is that you can go for higher aspect ratios (1000-10000 with dp) in boundary layer but you must avoid them in far field.

Minimum orthogonal quality required is 0.01 and if you are getting problem then you should check settings in Fluent, such as under-relaxation parameters, mesh scaling, mesh units, boundary condition etc..


Okay sorry about the lengthy post. However these are very general issues a lot of people face specially when you are a beginner. Remember none of the above is a must to do - it is just a good way to go - and of course there are other ways. There is too many ways tbh

Best Regards

Shereez
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