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[ICEM] Meshing of complex shape

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Old   January 10, 2012, 11:35
Default Meshing of complex shape
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Sijal Ahmed Memon (turboenginner@gmail.com)
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Hi Frends

I need your views/discussion for suitable topology of this configuration.
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Old   January 11, 2012, 12:47
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It is a very suitable candidate for ICEM CFD Hexa... pretty commonly done.

Take a quarter symmetry model and put it in a quarter cylinder... Hex mesh it with an Ogrid topology. The only tricky part is the tip where the quarter ogrid meets surface of the missile... There are various strategies that you can use if your missile is too sharp (yours does not look too sharp), but, in most cases, simply having a boundary layer around the missile gives you the flexibility you need to transition with reasonable quality.

I have seen some users block it in 2D on one side and then use 2D to 3D by rotation... This works well if you can handle wedges at the axis upstream and downstream of the missile.

You may also want to put an ogrid behind the missile to add refinement in that important wake region.

Then you can always copy rotate the quarter mesh into a full mesh and put it into any far field you want... You will probably end up with a rotating frame of reference for the missile.
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Old   January 11, 2012, 13:14
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I only use the hexa meshing, because it is my passion. I dont even think about any thing else

The missile shown here is image from some presentation available on net. In my case it is little bit different a) the front controlling surfaces have offset of 45 deg w.r.t fins at the tail. b) fins are about twice the size of controlling surfaces c) For both parts leading and trailing edges are round.

Should I model it as quarter model or as half model?

Quote:
I have seen some users block it in 2D on one side and then use 2D to 3D by rotation... This works well if you can handle wedges at the axis upstream and downstream of the missile.
Are you talking about the line singularity? Fluent is good at handling this stuff, but I don't prefer to have this in mesh Again it is my love for o-grid and ICEM is good at this
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Old   January 11, 2012, 13:26
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It is up to you, but I think it sounds like you still have quarter symmetry... You just have an interesting symmetry plane if you cut the symmetry plane to go right thru one of the fins (which is fine for meshing).

The rounded leading and trailing edges for the fins just suggests that you should do an Ogrid around them (possibly propagating from the fuselage to the far field) rather than a Cgrid.

As for the fins and control surfaces being out of alignment... You have choices. You could model them with different splits or you could just twist the blocking and handle them with the same splits. In other words, the topology of being out of alignment doesn't force you to mesh them that way... The decision would probably depend on how I thought the flow would go... I expect the missile will twist its way thru the flow anyway... So twisting mesh may actually capture the flow better...
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Old   February 7, 2012, 23:41
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Your suggestions are working well
Model is simplified
1. sharp trailing and leading edges are made round on both surfaces
2. nose is not included.
3. both fins are in line with each other.
4. Only quarter model is taken and after making mesh blocks were copied at 90 deg (3 copies) to make the model 360

Could you suggest, that how to make good topology for the fin tip (Fig 3) similar to DLR-F6 mesh presented at AIAA drag workshop. I tried after making the o-block around the fin but no success, I think I should have done it before making the o-grid, any comments please?

Last two pics are showing scan planes






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Old   February 7, 2012, 23:52
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Quote:
The only tricky part is the tip where the quarter ogrid meets surface of the missile...
I think I missed the point, could you please elaborate more. Your few words are more important than my months hard working.

Edit : tin and blocking files
Attached Files
File Type: zip quartermissle.zip (49.1 KB, 52 views)

Last edited by Far; February 9, 2012 at 02:25.
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Old   February 8, 2012, 22:03
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On the fin tip, you have tight geometry constraints... It is very difficult to get good quality if you turn the Ogrid around right there... But if you let the ogrid extend one block past the tip (either a little bit (on the scale of the fin thickness) or all the way to the wall), you will find that you don't have the tight geometry constraint and can turn the ogrid layer around without a problem...

Do you understand...?
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Old   February 10, 2012, 11:23
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Is there any way to have wake in multizone meshing while keeping O-grid?
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Old   February 10, 2012, 18:51
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We often use OGrids to fold mesh over to refine a wake region...

Or you could refine blocks... Fluent supports hanging nodes, but CFX requires you to setup a 3to1 refinement and then resolve refinements under edit mesh => Merge mesh...
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Old   February 13, 2012, 03:22
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Will you explain how to do this?
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Old   February 13, 2012, 13:15
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From your other posts, you understand mesh refinement.

Now for the Ogrid... Imagine the block behind your object (lets imagine a 2D case)... it is one block and the mesh is propagated across it in both directions... If you change anything, you get that change propagated and you can't change the refinement of that one block relative to the rest...

Now imagine that you put an Ogrid inside that block... You have now added a new index that you can refine as much as you want without it propagating beyond that block...

Best regards,

Simon
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Old   September 14, 2012, 07:44
Default ICEM-Hexa
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Hi,
I have updated the model with o-grids for the wings front and their tips. Quality achieved was 26%. Hope this helps you

Regards,
Raghav M S
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File Type: zip quartermissile_OGrid.zip (61.8 KB, 41 views)
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Old   September 14, 2012, 10:41
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Nice work. I am also interested to see more advanced topologies as Simon already indicated e.g. wake resolution with O-grid.
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Old   October 4, 2012, 06:13
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How would you go about continuing the blocking if there is something on this body that is not aligned with the direction of the fins such as suspension hangers or another set of fins at 45 deg to the ones in the original model?

In my attempt I've rotated the blocks so they are parallel to the fins as that is the main geometry sticking out of the body. But now I cannot see anyway to block around something that is also attached the to body but at 45 deg.
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Old   January 3, 2013, 14:36
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Hi every one
I have problem with my mesh my geometry by ICEM CFD (hexa mesh)
my geometry (quarter pipe diameter =0.011m, length pipe=1m, one perforation has diameter =0.006m, length above the wall of the pipe =0.003m, the distance of the perforation from the inlet of the pipe=0.8m)
can anyone help me how can I do the mesh of the pipe by hexa mesh?
and how can I find the friction factor and y+, k+, and epsilon+?
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