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-   -   [GAMBIT] Tet boundary layer (http://www.cfd-online.com/Forums/ansys-meshing/87340-tet-boundary-layer.html)

truffaldino April 18, 2011 07:46

Tet boundary layer
 
Hello,

I will be grateful for the following info.

Is it possible to create tetrahedral boundary layer with user-defined aspect ratio in GAMBIT:

In 2 dimensions you can split quad mesh or boundary layer in triangles (each quad cell splits diagonally in 2 triangles of the same aspect ratio).

Is it possible to do similar thing in 3d by splitting each hex cell in 6 tetrahedra?

If it is not possible, are there other ways of creating tet meshes with user-restricted element height?

Truffaldino

-mAx- April 18, 2011 08:13

if you use the BL panel, you can create either Hexa BL or Wedge BL. It depends on the surface mesh of the faces you want to appy the BL.
So you cannot create a BL with tetra .
In 2d you cannot split the quad-BL into triangles, because the BL isn't recongnize as a surface mesh. (understand you can split quads into tri only for 2d surfaces)
But what you can do: split your domain around your body (where you want to apply a BL), it will create a zone around your body, and you can mesh it at your own.
Here you can mesh it with tri (in 2d) or tetra in 3d.

truffaldino April 18, 2011 08:40

Quote:

Originally Posted by -mAx- (Post 304031)
But what you can do: split your domain around your body (where you want to apply a BL), it will create a zone around your body, and you can mesh it at your own.
Here you can mesh it with tri (in 2d) or tetra in 3d.

Thanks mAx,

I have already did my own 2d structured triangular mesh in the boundary zone by splitting rectangular structured mesh into triangles.

I thought i could do the same in 3d: create my own 3d structured hex mesh and then split every hex cell in 6 tethraedra, but I cannot find such splitting command in GAMBIT.

If there is a way to create structured tetrahedral meshes in GAMBIT?

Truffaldino

-mAx- April 18, 2011 08:46

you can unstructured but not structured

truffaldino April 18, 2011 16:21

Thanks mAx

It is pity that such a simple option is absent in GAMBIT. So it seems that one cannot create a 3d boundary layer mesh that switches to unstructured tet mesh on its top with approximately the same aspect ratio: one has either a strong jump in volume ratios of unstructured to structured or/and a strong jump in aspect ratio.

Truffaldino

SSPhoenix July 4, 2011 14:22

3d tetra mesh with BL Prismatic cells
 
Hello truffaldino,

I have run into the same problem I am afraid ... I am currently working on GAMBIT 2.4.6 x86 (but exceed is x64 apparantly), constructing a mesh for the NREL Phase VI UAE 10.0 m diameter Wind Turbine.

We are in the process of assessing flow control techniques on this blade, however meshing the baseline blade itself is proving to be a mission.

Anyway, more specific to the problem, through experimentation I found that it is possible to create a 3-D Tetra mesh that 'latches' on to a 3-D BL-mesh as discussed above, however - as you correctly state the size/aspect-ratio jump between the BL-cells and adjacent tetra cells is huge. One of the ways one can counter this is buy allowing the jump to occur and running a 'steady' calc in FLUENT - after sometime, one can enforce grid-adaptation within the solver.

My supervisor tells me it is quite a useful feature of FLUENT, and allows the user to 'tailor' the mesh wherever they please. My grid is STILL!!! not ready yet, thanks to more and more experimentation with GAMBIT, but I'm quite sure you can reduce the errors in the solution to acceptable levels once grid adaptation scheme is introduced.

What do you think -mAx- ? by the way, thank you for being so pro-active with these forums, you're a star :cool:

cheers


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