Learning Forum

[lu jia]

When I calculate the case for about 1s or less, the energy equation does not converge with the warning "temperature limited to 1 in 50 cells on zone 6(where is body mesh part)". The model is a group of alveolar in the lung，so  I use dynamic mesh to let the computational domain change with the time.

[Nikhil N]

Hello,

 

It appears that you are encountering an issue that may occur early on in your solution, but should improve as you continue to iterate. However, if the issue persists, it may indicate that the energy equation is struggling to converge, which can be caused by using a mesh of poor quality. Could you please provide me with the maximum skewness and orthogonality values of your mesh?

 

Thanks!

Nikhil

[lu jia]

OK, the max face skewness is 0.82, and the max cell skewness is 0.899. it  is 0.8 and 0.7 at initial time and rises with the time

 

[Nikhil N]

While a maximum skewness of 0.9 is acceptable, it's recommended to aim for a lower value of 0.7 or less. Additionally, it's crucial to check the minimum orthogonal quality of the cells in your mesh, as a low value can indicate poor mesh quality and negatively impact your results.

[lu jia]

The minimum orthogonal quality is 0.1. Is it too low? Maybe it's the mesh quality's problem.

[Nikhil N]

A minimum orthogonal quality value of 0.1 and above is acceptable, so we are good there. However, please try to improve the skewness value if possible.

[lu jia]

OK，thanks for reply

[lu jia]

Could you expalin the  skewness and orthogonal quality? I know something about the skewness, which maybe describes the surface and volume ratio.

[Rob]

Ortho quality is angle ratio based, and is (I think) covered along with some colour images in the Fluent Meshing documentation. Otherwise check in Meshing. It's OK to use on hex/tet elements but is really the only way to check poly cell quality. 

If you're hitting temperature limits check for mesh (as discussed) but also rate of change of volume. Which gas density model are you using?