I have a saved mesh from GAMBIT. I load it in FLUENT and when I do the check grid, it failes because there's non positive volumes. I did smooth & swap but no way to solve the problem. What I have to do??

Andrea

If it's 2D axisymmetric, then the problem is that your grid doesn't lie above the X axis. For 2D axi, Fluent requires that the X axis be the axis of rotation, and that the entire grid lies above the X axis.

If it's not 2D axi, then go back to Gambit and investigate the mesh there. If it's 3D, go to the Volume Mesh tools, and under the "Info" button is a "Check" command. Use this to check the mesh of your volume. If it's 2D, the same tool exists in the Face Mesh tools. This will tell you your max/min skewness and a distribution of them (how many cells fall into what range). Also, use the Examine Mesh tool (it's a button all the way to the bottom right of the screen... looks like a yellow grid with a magnifying glass) to find the location of the bad cells. Once you've found where the problem is, you can start working on ways of correcting the problem.

Hope this helps, and good luck, Jason

Thanks Jason, only one thing I have to ask you: how have I to do for examine the mesh and discover the negative volumes. I found the Examine Mesh tools but I don't know how to use it.

Andrea

Towards the top of the examine mesh too: turn on the range option (this will allow you to display cells based on how skewed they are... the plane option will plot cells that lie along a specified plane, and the sphere option will plot cells that lie a constant diameter from the origin). Select the type of elements you're looking at (2D/3D, and are they Hex, Prism, Pyramid, or Tet). Select the property you want to look at (typically you look at equi-angle skew to judge the quality of the mesh).

Towards the bottom of the examine mesh tool is a checkbox that says "Show the worst cell". If you click this, it will turn off all of the other cells and it will zoom in on the worst cell.

Instead of just zooming in on the worst cell, you can pick what range of skewness you want to show. Any cells that aren't within the range you specify are turned off. The downfall to doing this is that Gambit won't zoom in on these cells for you, so you have to manually find them all.

Play around with the other options to see what they do. Also, check out the Gambit manual. There's some info on the Examine mesh tool in there.

Hope this helps, and good luck, Jason

Thank you very much. Your suggests are very useful

Ciao Andrea

SEGREGATE GEOMETRY AND GRID AGAIN. BEST REGARD.

[roger_pn]

Hi everyone,

I have the same problem. I'm trying to mesh an aileron but when doing the Grid in Fluent it says I have non-positive volume and that the minimum volume is negative. Can someone explain what that means??

I've already looked at what Jason said (checked all the volumes, look at the Examine mesh, etc) and also done some volume smoothing. But nothing has changed. When I clicked at the check button it says that all volumes are valid, so I don't understand why afterwards it tells I have negative volumes.

Thanks for you're advices!!