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Old   October 7, 2012, 10:26
Default Airfoil Meshing
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Hello every body I'm new in this forum and I hope you will have a solution or informations about my problem. I'm trying to mesh an airfoil on STARCCM+ and it's a SELIG 4083 profile. So first I defined a volume around my profile in CATIA like a "C-grid" with a free stream and then I imported the STP in STARCCM+. My problem occures during the meshing. I have few problem with my different volumetric control. I created five blocks around my profile to be more accurate but when I mesh, the mesh considers only the smallest or the biggest volumetric control. Is there any interferences between each volumetric control or not ? Then the other problem is at the trailing edge of the profile because the trailing edge is sharp I have a bad mesh on the boudary layer and I don't know how to improve the mesh here. Maybe I can try to put a cylinder as a volumetric control.
If someone can bring me some help or if someone have ever meshed an airfoil in STARCCM+ his help is welcomed !
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Old   October 8, 2012, 03:41
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siamak rahimi ardkapan
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in the continua, click on mesh. In the property window, select preregion option. Then generate mesh, and see if it is solved.
good luck
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Old   October 8, 2012, 06:28
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Hello,

I made the change you asked me and the result is not better as you can see on the pictures following. I still have the problem with my different volumetric control and then I don't have a good boundary layer at the leading edge of my profile.
Any idea ?

Thank you for your answer and your help.

Below you can see first the mesh with the option you asked me to change and then without this option.






And here you can see what is the real problem, I have 5 different volumetric control but the mesh considers only one of them.

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Old   October 8, 2012, 07:16
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About the quality of the mesh, you can set small values for the airfoil. Try once without prism layer and one time with prism layer.
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Old   October 8, 2012, 08:27
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Hi,

I tried to mesh first without Prism Layer Mesher in the smallest volumetric control and then I tried with the Prism Layer Mesher in the smallest volumetric control and here is the difference with the change.





NB : this trial is made with a "Slow" default growth rate.

So I think it's better now but I still have a problem in the mesh. The problem is that now I have a segmentation of my profile. How can I improve this to stick to my real profile ? I decrease my base size from 0.5 to 0.4 and it's better but ahead my profile a small base size is useless. Any idea ?

Thank you
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Old   October 8, 2012, 08:35
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With 0.3 in my base size :

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Old   October 8, 2012, 10:31
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This is what I have with the version 7.04 of STARCCM+. Maybe there are problem of the displayer in STARCCM+ 4.04 :





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Old   October 8, 2012, 14:44
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Reduce the surface size at the airfoil boundary.
When setting volumetric controls, CCM+ will only consider the smalles value within a given area, so when a volumetric control is completely covered another one with the same or smaller custom sizes, the smaller vc will have no effect.

By the way, I suspect your prism layer thickness to be way too high. Try a smaller thickness.
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Old   October 8, 2012, 21:26
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I agree with Abdul099, you should reduce the surface size of the airfoil.

Btw is your leading edge airfoil doesn't looks like a curve at all. You can try put a volumetric control on the leading edge only and put smaller surface size. Then generate the surface mesh first to see whether you get the airfoil that you want (provided the CAD file is correct)
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Old   October 9, 2012, 05:38
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Hello,

I followed your advices and I reduced the surface size on my airfoil thanks to "custom surface size". I decrease the relative minimum size from 25 to 10 and it's visibly better at the leading edge but I lose accuracy at the traileng edge because I have cells too long compared with the boudary thikness as you can see on pictures. I will try with only on VC on the Leading edge and one on the trailing edge to see if there is any difference.



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Old   October 9, 2012, 08:19
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Re,

I tried a new thing : I didn't put any VC at the leading edge, I reduced only the surface size of the airfoil and I obtained a very good surface mesh which follow my geometry profile. At the trailing edge, I tried to put a VC and I obtained a mesh like you can see on picture but (tell me if I'm wrong) it's not a very good mesh for the trailing edge and I really don't know how to handle a shaped geometry with the meshing. I need someone throws light on this problem.

Thank you





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Old   October 9, 2012, 14:10
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Do you use prism layer ?
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Old   October 9, 2012, 15:38
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Yes I use prism layer in my mesh and in my VC
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Old   October 10, 2012, 02:49
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Try one time not to use prism layer, instead reduce surface size and also reduce the growth rate. Then see what will be the mesh situation. I hope it work
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Old   October 10, 2012, 18:29
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Cut the trailing edge. It's easier to mesh when the TE is not a sharp edge. And I still think your prism layer thickness is much too high.
And maybe you can think about the aspect ratio of your near wall cells...
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