CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   FLUENT (http://www.cfd-online.com/Forums/fluent/)
-   -   Non Posivtive Volumes (http://www.cfd-online.com/Forums/fluent/30244-non-posivtive-volumes.html)

K.MuraliKrishna August 30, 2002 09:38

Non Posivtive Volumes
 
Dear Fluent users

I created mesh in gambit, after importing it into fluent,while Checking Grid command it gives following errors WARNING: non-positive volumes exist.

minimum volume (m3): -2.795385e-08

maximum volume (m3): 2.517220e+00

total volume (m3): 1.155276e+0

Zone 52: 358056 right-handed, 4 left-handed

WARNING: Grid check failed.

at the time of exporting I found Two warnings in my Gambit Transcript window

^ WARNING(2) - d:: NO SUCH FILE OR DIRECTORY A default (unspecified) continuum entity was created. A default (unspecified) boundary entity was created.

K.MuraliKrishna

Taher August 31, 2002 14:12

Re: Non Posivtive Volumes
 
Hi murali, When you have non positive volumes it definetely means that your mesh is not correct and there are small regions with either very high skewness or that they are overlapping.Remeshing is the only solution to the Fluent error. The Gambit error of No file or directory I am not sure. But the other one is normal meaning it is creating a wall and a default interior. Hope this helps. Taher

sri September 1, 2002 10:42

Re: Non Posivtive Volumes
 
Hi Murali,

The left handed faces are what causing the problem.These can be removed in fluent through TUI.These can also be removed by reading the case file into tgrid.

Taher September 1, 2002 10:59

Re: Non Posivtive Volumes
 
Hi sri, I just wanted to ask how did you coclude that the left hand faces are causing the problem ? is this the case always? could you also please elaborate on TUI and how to read the case file into Tgrid. Thanks, Taher

sri September 2, 2002 03:39

Re: Non Posivtive Volumes
 
Hi Taher,

Left handed faces may be a reason.TUI is text user interface.you can repair the face handedness through TUI by following command :

grid/mz/repair-face-handedness

sri

Sridhar September 3, 2002 07:30

Re: Non Posivtive Volumes
 
Hi,

I think, most often than not, left handed cells do exist when there are some negative volumes, but the converse is not always true. If you have all positive volumes, still there might be left handed cells...so when you perform Grid check, at the end Fluent Displays..."Warning: Grid check failed". Because it is just a warning, Fluent will still let you proceed with the remaining case set up. You can even run your case and obtain a coinverged soln too but you cannot always trust the solution. Moreover, as per my experience, even the TUI command that Sri gave also does not always work to get rid of the left handed cells. Sometimes going back to the meshing and changing the node positions in the corresponding zone just a little bit may do the needy.

Sridhar.

sri September 3, 2002 11:42

Re: Non Posivtive Volumes
 
Hi Sridhar,

I absolutely agree with you.TUI doesn't always work in repairing the facehandedness.With left handed faces you cannot always trust the solution as the handedness of a face decides the direction of flux in your domain.

sri


All times are GMT -4. The time now is 20:23.