CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   ANSYS Meshing & Geometry (http://www.cfd-online.com/Forums/ansys-meshing/)
-   -   [ICEM] improving mesh quality (http://www.cfd-online.com/Forums/ansys-meshing/116730-improving-mesh-quality.html)

kannstmasehn April 24, 2013 04:28

improving mesh quality
 
hi all,

I have a question concerning my mesh for a cyclone separator. You can see the mesh quality in the added picture. The bad quality can be seen in the other picture. I am using Star CCM+ and the mesh has 4,000k cells. With k-epsilon it converges but not with k-omega sst. Does someone has some tipps for me? Do I need to improve the quality at that place? If yes, how can I do it? I did a refinement but it didn't really help. Should the mesh be over a quality of 0.7? Is there a difference between k-epsilon and k-omega concerning the mesh quality?

thank you very much

http://s7.directupload.net/images/130424/kwwky9in.jpg

http://s14.directupload.net/images/130424/a9vznlhr.jpg

energy382 April 26, 2013 06:15

Quote:

Originally Posted by kannstmasehn (Post 422756)
hi all,

I have a question concerning my mesh for a cyclone separator. You can see the mesh quality in the added picture. The bad quality can be seen in the other picture. I am using Star CCM+ and the mesh has 4,000k cells. With k-epsilon it converges but not with k-omega sst. Does someone has some tipps for me? Do I need to improve the quality at that place? If yes, how can I do it? I did a refinement but it didn't really help. Should the mesh be over a quality of 0.7? Is there a difference between k-epsilon and k-omega concerning the mesh quality?

thank you very much

http://s7.directupload.net/images/130424/kwwky9in.jpg

http://s14.directupload.net/images/130424/a9vznlhr.jpg

Please make a angle and det 3x3 plot and use another color, as the mesh is imperceptible.
If avaiable, upload blocking file or provide some pics.

Quality criterion isn't that important. Angle and orthogonal quality are more important in my point of view. Make a mesh independence study (coarse, reference, fine mesh) and look, who the variable of interest changes.

What kind of simulation will you run....transient? And is there any heat exchange etc..?

RodriguezFatz April 29, 2013 02:31

1) I agree, but that quality looks horrible. This is a hexa mesh, right? You will definitely be able to improve that. Can you show us some pictures of the blocking at the relevant locations?
2) This looks like some cyclone. Don't worry if not every single turbulence model will converge. Some are just not made for these strong swirling motions. Altough both models are not made for that purpose, k-e converges anyway... that doesn't sound unusual.
3) Please tell us the settings of your solver (especially solution methods: discretizations)! If you don't already do that, give this a quick try: Set pressure to "body force weighted" and try again with k-w.

kannstmasehn April 29, 2013 03:23

I made some screenshots for you. I hope they can help.

Here is the blocking

http://s1.directupload.net/images/130429/q7hd7hbn.jpg
http://s7.directupload.net/images/130429/77ln8dph.jpg

A link to another blocking picture:
http://s14.directupload.net/images/130429/5cm6q9gv.jpg


Here the quality is shown:
http://s1.directupload.net/images/130429/ge6qt9g9.jpg
http://s14.directupload.net/images/130429/8p967hlx.jpg
http://s7.directupload.net/images/130429/e5pwcwyz.jpg


http://s7.directupload.net/images/130429/hrl67tim.jpg


Here are my settings for the k-omega.


http://s14.directupload.net/images/130429/rj9prbkj.jpg
And here are my settings for the solver.
http://s7.directupload.net/images/130429/l9vk65n7.jpg
http://s1.directupload.net/images/130429/d9qmemzd.jpg
http://s1.directupload.net/images/130429/t2m8becw.jpg


Thank you very much!

RodriguezFatz April 29, 2013 03:50

Ok, maybe someone else can help with the solver settings in StarCCM - I just know Fluent.
Can you upload the ICEM files (geometry and blocking)? I would like to give it a try...

kannstmasehn April 29, 2013 04:12

1 Attachment(s)
i hope the .tin file is right for the geometry, is it? both files are in the .zip file

RodriguezFatz April 29, 2013 04:45

2 Attachment(s)
Alright! Still disappointing, but I was able to enhance the grid partially.
Look at the picture:
Attachment 21249
1) Disassociate the edge and the vertrex from geometry.
2) Now associate the two faces to the wall and the edge (2b) to the outer radius+the inlet curve
3) You will be able to move the vertex to the right, along the linet curve.

The green region is much better now. The blue region is still bad. Unfortunately the same trick doesn't work here, because your outer cylinder goes further down.
Attachment 21255
Maybe someone else has a good idea.

kannstmasehn April 29, 2013 05:08

ok thank you, I'll give that a try.

BrolY April 29, 2013 05:28

That's the big problem with such a geometry. You will always have bad elements quality. For this kind of geometry, the min angle is the most critical quality criterion. As you can see, your determinant is very good (>0.2 is often good for any solvers), but your min angle is awful (<9 is often very bad most of solvers).

Adding a 1/4 of Ogrid at the junction would probably help.
Search on this forum about cyclone, that's something we have already worked on ;)

About the differences between k-eps and k-omega, the Y+ is not the same, and so is the length of your first layer !!!


All times are GMT -4. The time now is 14:27.