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-   -   [GAMBIT] Asking size function... (http://www.cfd-online.com/Forums/ansys-meshing/71333-asking-size-function.html)

teguhtf December 26, 2009 06:51

Asking size function...
 
Hi Everybody,,
In meshing banki water turbin. i have problem in controlling pattern of meshing. I've read that it can be solved by size function. I've tried to apply the step from "gambit tip & trick" but it can't work. Can you help me out my problem?? do you have reference??
thanks:D
teguhtf

-mAx- January 4, 2010 05:13

check User Guide, size functions are well described

dralosdir January 4, 2010 16:00

i have problems with the size function too. i dont think they are that well explained in the online help for someone who is unexperienced.

i have a simple airfoil and an outerflowfield. i want to create a mesh which is fine near the airfoil and gets bigger at the flowfield borders. what do i need to set as source and attachment?

and what values should i use for start size, growth and size limit.

thanks

teguhtf January 4, 2010 17:28

Quote:

Originally Posted by -mAx- (Post 241412)
check User Guide, size functions are well described

thanks max. I have understood it. But my geometry is complex enough hence i cannot apply size function easily. I have tried to make inflated boundary but it cannot work so i just mesh in high density of mesh around the blade.

teguhtf January 4, 2010 17:33

Quote:

Originally Posted by dralosdir (Post 241465)
i have problems with the size function too. i dont think they are that well explained in the online help for someone who is unexperienced.

i have a simple airfoil and an outerflowfield. i want to create a mesh which is fine near the airfoil and gets bigger at the flowfield borders. what do i need to set as source and attachment?

and what values should i use for start size, growth and size limit.

thanks

Hi
check this out!! www.anova.com.tr/dosyalar/destek/gambittips.pdf
Maybe it can help you out your problem.
By the way, for smooth mesh near wall, why you don't use boundary layer mesh?? i think its great to get drag value!!
teguhtf

-mAx- January 5, 2010 02:22

for complex geometries, you need to split your domain into several smaller subdomains.
You will have more control on your mesh

dralosdir January 5, 2010 09:54

thank you for your help.

the thing i am doing is for a schoolproject. we are told to find the cl of an airfoil. we need to create a boundary layer around the airfoil and then us tri/pave for the mesh.

i attached some pictures so that you can see what i mean. the outerflowfield is a face and the innerflowfield is a face too.

if i now use the size function and pick the edges of the airfoil as source and the innerflowfield face as attachment it doesnt quite seem to work. i dont get a mesh at all. maybe someone of you knows some good values i need to enter?

outerflowfield:

http://i45.tinypic.com/ixf8rn.jpg

innerflowfield:

http://i45.tinypic.com/210hmow.jpg

-mAx- January 6, 2010 02:02

we can't see the pictures

PSYMN January 6, 2010 12:31

I can see...
 
I can see the pics... Maybe it is because I wear these cool shades :cool:

dralosdir January 6, 2010 13:44

i dont know why max cant see the pictures. maybe you have an adblocker which blocks tinypic?

anyways, i figured out how to use the size function now thanks again for your help.
the next problem i have is that i have a negative volume (i am in 2d though, dont know whats happening) somewhere in my mesh when i read it into fluent.

teguhtf January 6, 2010 20:01

Quote:

Originally Posted by dralosdir (Post 241662)
i dont know why max cant see the pictures. maybe you have an adblocker which blocks tinypic?

anyways, i figured out how to use the size function now thanks again for your help.
the next problem i have is that i have a negative volume (i am in 2d though, dont know whats happening) somewhere in my mesh when i read it into fluent.

You can check the worst element of your mesh and repair it. I think that is the troublemaker of your case.
teguhtf

teguhtf January 6, 2010 20:04

Quote:

Originally Posted by -mAx- (Post 241491)
for complex geometries, you need to split your domain into several smaller subdomains.
You will have more control on your mesh

Thank's max, I'll try that!!!:D
teguhtf

-mAx- January 7, 2010 01:52

In Gambit go to examine mesh.
Choose Volume, and set the max value to 0.
It will show you all cells with negative volume

dralosdir January 7, 2010 01:53

Quote:

Originally Posted by teguhtf (Post 241696)
You can check the worst element of your mesh and repair it. I think that is the troublemaker of your case.
teguhtf

i think i have one element with a negative volume and 10 left handed elements. how can i find those?


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