I´m moleding a jet fan with FLUENT 6.3. I have three volumens in domain for inlet, rotor and oulet. FLUENT display a non-positive volumes warning with unsteady solver and moving mesh in boundary conditions panel but not with moving reference frame condidition. Would be related to mesh skewness?. Wrong definition of the boundary layers?. Any other reason?.

Excuse my poor english.

Thanks.

The only time i got that warning is when I attempted to use the 2d axisymmetric solver while choosing the wrong axis for the symmetry. I believe fluent uses the x axis by default and this cannot be changed. This probably doesnt help you because im sure there are many more reasons for this warning to come up.

Hi,when your doing the problem with MRF you no need to update the mesh so at that time there is no question of non-positive volume,but when you use moving mesh based on the skeness you will get non-positive volumes try to modify meshing parameters ok..

Hi, If you are using moving mesh with structured mesh (hexa in 3D or cuad in 2D) you can´t use the spring smoothing method, then you have to use the layering method to avoid negative volumes formation.

I hope this helps you!

"If you are using moving mesh with structured mesh (hexa in 3D or cuad in 2D) you can´t use the spring smoothing method, then you have to use the layering method to avoid negative volumes formation."

No.I´m using unstructured mesh. But probably it´s a mesh algoritm question in Gambit. I have some problems with meshing.

Thank you to all!

So, you have the first warning in Gambit? In that case, try to improve the mesh in the most complicated zones of your domain. Sometimes very very high skewed elements couldn´t be handled by Gambit so they were turned in negative volume cells. Regarding a Fluent warning I can say from my experience that always that Fluent gave me that message was enough to remesh the domain with better quality.

Good luck!

"Sometimes very very high skewed elements couldn´t be handled by Gambit so they were turned in negative volume cells."

Yes, it is probably that happen.

Thanks HSeldon.