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Prism Layer in STAR-CCM+

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Old   December 29, 2008, 22:24
Default Prism Layer in STAR-CCM+
  #1
Antimony
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Hi,

I am trying out the flow over the RAE2822 airfoil. I am having difficulty in getting a nice quality prism layer mesh at the trailing edge of the airfoil. Somehow, the software always retracts the prism layer near the trailing edge in a linear manner and in the process, the prism layer thickness is lost at the end(the thickness should be about 1mm, but I am getting it to be far lesser than that).

Would anyone know how to sort this problem out? I have tried everything and yet have not managed to solve the problem. Would be extremely grateful for any help in this matter.

Thanks in advance.

Antimony
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Old   December 30, 2008, 00:21
Default Re: Prism Layer in STAR-CCM+
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adsfg
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The prism layer mesher tries to maintain a distance between vertices, not edges, so anytime you have a sharp convex angle the prism layer will get smaller. This is not a bug, the wall functions are not going to be valid over such a sharp convex corner anyway.

You should put a feature curve on the trailing edge of the airfoil. In v3.04 and above you can specify surface size on feature curves, so you can refine the trailing edge to capture the flow there better.
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Old   December 30, 2008, 03:13
Default Re: Prism Layer in STAR-CCM+
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Antimony
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Hi,

Thanks for your reply. If I have understood what you have said correctly, the more the number of vertices towards the trailing edge of the airfoil, the better my chances of getting a good prism layer mesh at the trailing edge. Correct?

If that understanding is correct, then somehow I am still not getting things proper here. I created the feature curve on the trailing edge, but whatever custom size I specify, nothing seems to work. The mesh still converges in a linear fashion with or without the custom size. Any suggestions as to where my mistakes lie?

If my understanding is not correct, could you please tell me where I am wrong?

Thanks

Antimony
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Old   December 30, 2008, 03:33
Default Re: Prism Layer in STAR-CCM+
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Antimony
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Could I also ask you how you know that the prism layer mesher works with vertices instead of edges? Is it there in the training guide?
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Old   December 30, 2008, 11:47
Default Re: Prism Layer in STAR-CCM+
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adsfg
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I can just tell by how the prism layer looks. Look at your trailing edge vertex and the prism layer vertex associated with it, they are the same distance apart as all the other vertices.

Like I said though, you will not get the mesh you are trying to obtain. There is no reason to try and get the prism layer perfect on the trailing edge, because all of the boundary layer assumptions are invalid there anyway. You just need to put more cells there.
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Old   January 5, 2009, 12:29
Default Re: Prism Layer in STAR-CCM+
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navaladi
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Hi Antimony,

Unlike Proam, starccm mesher has limited options for prism layer meshing.

Have you tried, "Boundary march angle", "Concave Angle limit", and "Convex angle limit".

If they does not work, you should resolve , i mean geometry approximate trailing edge of a Airfoil. that could help.

try to get help from support , if not.

All de best

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Old   January 6, 2009, 00:57
Default Re: Prism Layer in STAR-CCM+
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Antimony
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Hi Navaldi,

Thanks a lot for your message. Yup, I tried changing the boundary march angle, concave angle limit as well as the convex limit. None of them seem to work.

Guess my only option as you have rightly said is to play with the trailing edge geometry.

Thanks once again for your message.

Antimony
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Old   July 1, 2009, 11:54
Default interface use
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You can actually use a transparent interface that will be attached to the trailing edge of your foil to make sure the prisms layers end further downstream. The collapse will still exist but if you tune the interface size properly, should occur in a much less critical zone.

Cheers, Dimitri
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Old   July 2, 2009, 03:14
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Can you make some screenshots of your solution? I don't understand it complete.
I have the same problem. I used a offset in the mesh to get a little bit better cell quality but the courant number is in some cells after a edge very high but so solution looks good there...
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Old   July 2, 2009, 05:55
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Sorry I dont kno how to import easily a pic in here, if you email me dimitrivlc@gmail.com I can send you an image. The idea is the following: you create a surface that is attached dowstream of your trailing edge, then you declare this surface as an interface (transparent of course for the flow) but, in the interface properties, you prescribe the BL extrusion to be performed on both sides.
Hence, the BL, instead of stopping sharp on the TE will carry on downstream. It is not perfect but it allows to move the BL collapse away from a critical flow zone.

Cheers, Dimitri.
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Old   July 2, 2009, 06:15
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You only have to click on "Post reply" and then you can attach files
I have wrote you an email.

I have attached my problem.
On one edge there is no problem but on the other. On both edges are 2 "channels". The channel with the problem is double in the size - 2D simulation!
Attached Images
File Type: png shot.png (6.6 KB, 199 views)
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Old   July 2, 2009, 06:26
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file:///C:/Work/profil/test%20tail/tail.jpg
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