I am new to gambit. I made my geometry and I can create a mesh for it and the CFX solver uses it ok.

My problem is this: there are a number of cylinders in a channel. Most of the cylinders are big (2 inches). One of the cylinders is tiny (0.125 inch). When I create the tet mesh for this region the tets grow too fast. How can I make the elements expand more slowly? I'm not using boundary layers.

Is your model 2d or 3d?

3D

oh wait, tet is 3d. just realised. Did you try changing the ratio scrollbar on the mesh lines window?

Alternatively, I think you can go to Adapt --> gradient and mark cells for "coarsen" instead of refinement. More details are available on the fluent tutorials provided (Im not sure which tutorial it is but if you search through the user guide in PDF, you can search for the word "gradient" in each tutorial and you should find the full procedure there somewhere)

Use a size function - one of the menus at the top of the right hand side has it in it.

Have you considered using cooper to extrude a mesh through the model? There are tutorials in the documentation that explain it.

If you use a size funtion you can stipulate the speed the grid grows at, away from a wall, volume, etc. 1.2 should be reasonable but you can go higher or lower.

Phil

I don't know how to use the sizing functions. Cooper won't extrude through the region because there are holes drilled in the sides of the cylinders. I tried specifying a size function but it wants 2 volumes. What do I choose for the 2 volumes? I tried using the same volume for both selections and specifying my mesh parameters, but when I try to generate the mesh after that it sits there a long time (hours) generating the sizing function and never produces a mesh.

I split the volume such that the small cylinder was separated from the others. I meshed the volume around the small cylinder with very fine tetrahedra and the rest with coarser tetrahedra.