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-   -   [ANSYS Meshing] How to find the correct defeaturing tolerance? (http://www.cfd-online.com/Forums/ansys-meshing/107604-how-find-correct-defeaturing-tolerance.html)

koskey October 2, 2012 10:37

How to find the correct defeaturing tolerance?
 
1 Attachment(s)
Hello!

I have been trying to create a mesh for an airfoil in workbench, and it seems that once I change the airfoil geometry from the tutorial one I get the following warning.

"The default defeaturing tolerance was larger than one computed based on size controls. The mesher has modified the global defeaturing tolerance accordingly."

And makes one quadrant of the mesh a bit weird like so.. Attachment 15985

Does anyone know how I can make it match the rest of the mesh? I'm assuming it's a easy question but i just don't know where else to find the answer..

Thanks guys,
Koskey

Archer_CFD October 28, 2012 21:43

Hi,

Did you eventually find a solution?

I am having exactly the same problem.

Cheers.

koskey October 28, 2012 22:38

No I didn't figure it out. I ended up changing the project up a bit because of it, but would love to know how to make it work still

Archer_CFD October 31, 2012 21:17

1 Attachment(s)
I managed to contact a researcher at my university who works with Ansys regularly and he was able to help me out.

I assume that, like me, you used the airfoil tutorial at this website?
https://confluence.cornell.edu/displ...+Specification

When I substituted in a NACA4415 instead of the NACA0012 used here I had the same mesh problem as you except mine was in the top left quadrant. In this case, what worked for me was adding an extra edge sizing to the top surface of the airfoil with the same number of divisions as the inlet curve in that quadrant.

The problem also occured with heavily undercambered airfoils. The meshing method from the above tutorial couldn't handle the underside curve. The solution was to add an extra partition to the C-grid so that it could handle the curve as shown in the figure below.

Attachment 16553

As for your exact problem. The only time either of my right hand side quadrants failed to mesh properly was when the plane used to draw the C-grid (plane 4 in the tutorial) was not exactly over the trailing edge of the airfoil. When it happened to me, my trailing edge protruded into the upper-right quadrant by 1/1000th of a millimetre, causing the upper-right quadrant to fail in the same way as yours.

As far as I can tell. The meshing failures that we're seeing have nothing to do with the defeaturing tolerance. It's just that ICEM CFD is not smart enough to generate the mesh without further help. The researcher who helped me opened my files in a later version of Ansys (v14) and they worked for him straight away and we could only solve my problems by opening them in Ansys 13.

I hope that any of this was useful to you.


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