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-   -   [ICEM] low edge criterion value problem (http://www.cfd-online.com/Forums/ansys-meshing/116354-low-edge-criterion-value-problem.html)

mraxx April 17, 2013 12:09

low edge criterion value problem
 
2 Attachment(s)
Hi,

I am trying to create an unstructured mesh for the fluid domain around an airplane. With the default value of 0.2 for edge criterion in ICEM, the trailing edge of the airfoil looked very rugged. So I tried to lower the edge criterion. But If I go lower than 0.02, ICEM does not capture the geometry anymore but simply meshes through the whole airplane, see first attached picture.
Can somebody tell me why this happens and how to deal with it?

Another problem that I have is shown in the second attached picture. I use the symmetry of the flow, so I have a symmetry plane through my airplane. Unforunately, some of the faces belonging to this symmetry plane part are out-of-plane. I have to allow approx. 30 deviation from the plane in CFX to even start the solver.
I guess the faces that cause those problems are the ones on the tip of the fin. Any suggestions how to fix those faces?

Thanks in advance!

diamondx April 17, 2013 12:13

have you performed a build topoligy in the geometry tab ??

stuart23 April 18, 2013 00:56

Be careful with edgec, too low and your mesh will be full of degenerate errors, too high and you will get the "serrated" effect. Unfortunately, as with many things, it is a matter of balancing robustness with performance. If the parameter could be lowered without any side effect, the default value would be 0!

If you need a cusp trailing edge, maybe try using Define Thin Cuts?

Stu

stuart23 April 18, 2013 01:05

PS Good too see that you have defeatured your geometry! I laughed so hard when I first saw your model with the Jetstar logo. I think Jetstar have more pressing issues than performing CFD simulation. Perhaps providing any customer service........

mraxx April 18, 2013 08:50

1 Attachment(s)
Quote:

Originally Posted by diamondx (Post 421276)
have you performed a build topoligy in the geometry tab ??

Actually, I didn't. But when I do it now, ICEM always freezes when I try to create the mesh. The attached picture shows where the freeze occurs.


I also thought about defining thin cuts. But I realized that also lowering the element size on the wing-parts results in a mesh that ignores the boundaries.

diamondx April 18, 2013 09:00

put the surfaces in different parts. if you have an edge separating two surfaces , and if the angle between the two is considerable, separate them. for your wing, put extrados in "TOP" and intrados in "down", see if changes anything

mraxx April 30, 2013 09:03

So I was finally able to generate a mesh after building the topolody. But I still have the same problem. If the edge criterion is too low, the mesh goes through the boundaries.

I did put the top and bottom surface in different parts and additionally i defined a thin cut. But I still have a very rugged trailing edge.

Any more suggestions?


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