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Prism Layer - Core Mesh Boundary Issue

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Old   November 4, 2017, 11:39
Default Prism Layer - Core Mesh Boundary Issue
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Conor Crickmore
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Hello everyone,
I'm encountering a rather odd issue that no amount of tweaking seems to resolve, bare in mind I am new to CFD and STAR so I may be doing something stupid.

I am getting a tiny (like in the same order of magnitude as the Near Wall Cell) cell forming between my outermost prism layer and my core mesh but only on my geometry walls (not the roof, floor and wall of my 'Wind Tunnel')

Alongside this, I am also getting a strange collapse-like issue at the trailing edge of the geometry. The Prisms aren't actually collapsing, and are continuing along the geometry.

Visual representations can be seen here.

I'd tried changing the thickness, number of layers, and numerous other parameters and nothing seems to rid me of this issue.

Again, apologies if this is a simple issue/non-issue that I am unaware of,
Thanks
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Old   November 8, 2017, 10:41
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it is not clear what your are showing in those images and are you sure you are looking at prism cells anyway

do other sections and also use the prism layer field function to clearly show where prisms layers are in a scalar scene cross section
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Old   November 9, 2017, 00:12
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You are seeing an artifact of using a cutting plane. The cutting plane is not perfectly cutting through only one sheet of cells in a plane, it cuts through all of them. So you will see small wedges and weird shapes where a cell has been chopped.

If you want to see the actual cells use a cell surface.
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Old   November 9, 2017, 08:53
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to see the actual cells it is better to use a threshold since cell surface only show the first layer
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Old   November 9, 2017, 09:28
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I don't agree with that. A cell surface can show any 'layer' of the mesh if you give it a plane section as input. Getting a slice of whole cells in a mesh with a threshold is difficult and expensive.
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Old   November 13, 2017, 01:34
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you are correct me3840 i forgot cell surface is not just for boundaries

and it can be enhanced considerable by using this new derived part in a scalar scene using the prism layer cells field function which clearly shows which cells are in the prism layer and the rest as shown in the attached image but this feature only works if you mesh using the newer parts based meshing which you should be using anyway these days
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File Type: png prism-layer-display.png (42.1 KB, 13 views)
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Old   November 14, 2017, 19:37
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Hi Conor Crickmore.. I graduated from Lboro a few years ago.. are you doing the CFD module with Henk?

Regarding your issue.. Have you enabled the surface wrapper / surface remesher?

Sometimes things like that happen as a result of the specific geometry and the algorithms that generate the mesh.. often you can just ignore them unless they present a serious problem to your simulation such as divergence or other nonphysical results..
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Old   November 21, 2017, 15:46
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Quote:
Originally Posted by macchesney View Post
Hi Conor Crickmore.. I graduated from Lboro a few years ago.. are you doing the CFD module with Henk?

Regarding your issue.. Have you enabled the surface wrapper / surface remesher?

Sometimes things like that happen as a result of the specific geometry and the algorithms that generate the mesh.. often you can just ignore them unless they present a serious problem to your simulation such as divergence or other nonphysical results..
I'm actually a fourth year doing a CFD-based FYP, I did do that module last year but it is run by Andrew Garmory now.

Speaking to Andrew, it does seem like this particular issue is just an artefact of the the plane 'cutting' the 3D cells as, as you said, it doesn't seem to be causing any serious issues.
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