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-   -   [ICEM] Delnauy technique "Bottom-up" problem (http://www.cfd-online.com/Forums/ansys-meshing/122749-delnauy-technique-bottom-up-problem.html)

m5edr August 27, 2013 07:44

Delnauy technique "Bottom-up" problem
 
Hi all,

I spent long long time to build a good mesh of my wind turbine blade ( and its enclosure) using octree tetra technique "top down" and after I sent the mesh to Fluent I discovered that the leading edge of my blade need to has dense surface mesh so I restart and replace my ICEM technique and follow the famous Workshop "Wingbody" that depend on Delnauy technique "Bottom-up"...

The "Wingbody" workshop started by setup curve sizes on leading edge , then start shell mesh, build the prism and finally fill the volume.

I followed and applied carefully the same steps of the "Wingbody" workshop on my model but i found this:

1- incomplete prism on the blade surface in spite of max. prism angle was set to 180

2-if I continue to build the volume using Delnauy technique an error appear called "tri2tet exited"
Any help and thanks in advance

m5edr August 29, 2013 07:51

1 Attachment(s)
I also followed the same steps of WingBody tutorial that created by @Far http://www.cfd-online.com/Forums/ans...tra-prism.html

but the prism looks like this (pic)

Any help pls.

PSYMN September 1, 2013 15:57

My guess is that the element quality of folding the prisms around that curve was just too low. You could lower the min quality to get more prisms, but...


When I have a sharp trailing edge, I typically create a trailing edge surface... Basically just use the surface creation tools to extrude the trailing edge surface backward for some distance... Or copy the trailing edge curves some distance backward and create a surface between the curves. Make sure the trailing edge is in a part like "TEMP". Make sure you checkbox the TEMP part for both Prism growth and Internal Wall. When you are done generating the mesh, you can either delete the "TEMP" shells from the mesh or mark them as "Internal Wall" in your solver.

m5edr September 2, 2013 16:09

Thanks Simon for reply , I appreciated that

Quote:

Originally Posted by PSYMN (Post 449248)
My guess is that the element quality of folding the prisms around that curve was just too low. You could lower the min quality to get more prisms, but...

I tried that , the min quality was set to 0.00000001, but the prism fault occurred

Quote:

Originally Posted by PSYMN (Post 449248)
When I have a sharp trailing edge, I typically create a trailing edge surface... Basically just use the surface creation tools to extrude the trailing edge surface backward for some distance... Or copy the trailing edge curves some distance backward and create a surface between the curves. Make sure the trailing edge is in a part like "TEMP". Make sure you checkbox the TEMP part for both Prism growth and Internal Wall. When you are done generating the mesh, you can either delete the "TEMP" shells from the mesh or mark them as "Internal Wall" in your solver.

1- is this will correct the prism fault or only improve quality?
2- could i ask you to share a link for tutorial or video for extruded the trailing edge (i can't understand this steps)

tanks in advance

brunoc September 2, 2013 21:18

Quote:

Originally Posted by m5edr (Post 449420)
1- is this will correct the prism fault or only improve quality?

It'll do both.

Quote:

Originally Posted by m5edr (Post 449420)
2- could i ask you to share a link for tutorial or video for extruded the trailing edge (i can't understand this steps)

The trailing edge has a curve. Extrude that curve to create a small surface pointing outwards of the blade (you can do this with 'Geometry > Sweep Surface' or 'Geometry > Surface of Revolution'). Put this new surface in a temporary part, like TEMP.

When creating the mesh, set TEMP to be a internal wall and activate prisms on this wall. You can do that in the prism setup window ('Mesh > Part Mesh Setup').

Re-generate your meshing as you normally do.

Cheers.

PSYMN September 2, 2013 21:22

1) I think the actual minimum that it will accept is 1e-6 for quality.

2) The trailing edge surface will improve the prism quality which will then allow prism to grow as you expect

3) I have posted threads on this topic before. I just went to look for the old pics I took, but couldn't find them...

m5edr September 4, 2013 05:00

1 Attachment(s)
o.k i did the extruded trialing edge and followed the mentioned steps but the prism fault is the same :confused:

i uploaded the new file http://www.4shared.com/rar/bf0GN7Aa/model.html
and here is a sample image of prism

m5edr September 4, 2013 06:24

1 Attachment(s)
also I tried to increase the shell meshing elements (increase blade curves nodes) but also the prism fault occurred (the total elements reach to 3 million without volume mesh!)

PSYMN September 4, 2013 13:23

The trailing edge surface should be longer (at least the element size times the number of layers) and did you make sure to set the "internal wall" and "prism" check boxes for the new surface? It needs to have triangles on it and prism needs to grow from those triangles.

m5edr September 4, 2013 13:53

1 Attachment(s)
thanks simon for reply

Quote:

Originally Posted by PSYMN (Post 449893)
The trailing edge surface should be longer (at least the element size times the number of layers)

o.k, what should i do for this?


Quote:

Originally Posted by PSYMN (Post 449893)
and did you make sure to set the "internal wall" and "prism" check boxes for the new surface? It needs to have triangles on it and prism needs to grow from those triangles.

yes , i upload an image for Part Mesh setup

PSYMN September 4, 2013 14:06

Actually, I guess you were using patch conforming mesh right? THe internal wall thing is just to prevent octree from deleting the mesh so there will be mesh for prism to grow from... If you are using another method, the key thing is to make sure you have a surface mesh in the TEMP part.

As for how to make the trailing edge surface longer, just do what you did before, but longer. If you did it with a copy transform of the curve, just copy/transform it further away.

Basically, what is happening is the mesh is stair stepping away from the bad area... You want to create a trailing edge surface so that the stair stepping is happening on the trailing edge surface instead of the wing.

m5edr September 6, 2013 16:33

Hi Simon
Quote:

Originally Posted by PSYMN (Post 449906)
Actually, I guess you were using patch conforming mesh right?

yes

Quote:

Originally Posted by PSYMN (Post 449906)
As for how to make the trailing edge surface longer, just do what you did before, but longer. If you did it with a copy transform of the curve, just copy/transform it further away.

I did this (Geometry>> sweep surface), when i made the egde surface longer , the prism is done inside the blade :confused::confused: . If i make the surface longer than the previous an error massage appear and the prism building stop.

m5edr September 8, 2013 08:34

prism setting...
 
1 Attachment(s)
This is my prism setting (image) ....

Any suggestion?


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