I have particular airfoil and I need to calculate air flow. I made very thin 3D sector (extruded airfoil on 20 cm) and built domain boundaries around this sector. So now I have very thin 3D box (about 11000 cm length and width and 20 cm thickness) What I want is to generate tetra mesh but I face a lot of problems. I guess this is because of very thin 3D box. Maximum size of tetrahedral element must be much more than 20 cm (about 500 cm) and mesher can't insert such tetrahedral element correctly. On the other hand minimum size must be about 1 cm near airfoil to catch all differencies in flow. Please advice me how to build mesh in my situation?

hi am not able to understand the problem clearly. if you can post the image of the geometry, then i can help you.

Thank you

Unfortunately I'm not able to post image right now ((( Just imagine that you have very thin 3D box with XYZ-size (10000, 10000, 20). So X and Y are much more than Z. Also imagine that inside this 3D box (just in center) there is a blunt body (like cube) with XYZ-size (10,10,10). Now I want to build tetra mesh. To do this I set maximum size near blunt body to 1 and Global Size to 500 (size of tetra closer to planes which form 3D box). ... Mesh generation fails. Note that if I generate mesh in, for example, cube with XYZ-size (10000, 10000, 10000) everything is fine.... I suppose that the reason of failure is the fact that mesher can't build tetra inside 3D box with edge more than 20.

Yes, this will not work. But the more sensible approach would be to to build a small tetra mesh around the area of interest, and then extrude the faces of this mesh in your X and Y directions. Don't try to generate it in one go.

Could you tell me how to do this extrusion? And how to set such kind of area of interest around the body?

I also tried to build mesh around blunt body using blocking and actually I built it. But then I must build small tetra mesh around blunt body ans somehow to connect this with blocking mesh but I don't know how...

Your question is not actually very clear. Your first question makes it sound as if the grid really needs to be 2-dimensional with a 20 cm cell in the third direction. Your second description is different, it sounds as if you want a 3-dimensional grid with a thin third dimension. If your requirement is really for a 2D airfoil, like you originally said, it is much better to do a pure 2D grid (triangular if you really need that, but it sounds like structured quad would be better), and extrude that in the third direction.

If on the other hand, you really need a very thin 3D mesh, then the best option is to do a small refined region around your body using more or less isotropic tetrahedra, then take the boundary faces and extrude them to the far boundaries.

Ok, let me clarify. I meant second description and I want a 3-dimensional grid with a thin third dimension. Could you tell how to set (in outline) this small refined region around my body and how to exrude boundary faces to the far boundaries?

Build a small closed set of surfaces around your body of interest, and create a tetra mesh in there. Then take the outer faces of that mesh block and extrude them out to your real boundaries.