[giorgianig]

Dear all, I am trying to mesh a T-junction of 3 pipes. Here is the geometry







I would like to mesh the 3 rectilinear section with a 3D extrusion, and the T-junction in the middle with an unstructured mesh of tetrahedra. I also would like to have a boundary layer on the walls. So, I generated a partition and exploded in 4 solids: 3 cylinders and a T. See figure:






Then I generated a submesh on the faces connecting the cylinder and the T, and another submeshes for the extrusion of the cylindrial meshes. So far, so good, see picture:





Also you can notice a nice boundary layer on the cylinders





Now, I define the global mesh as Netgen 3D, put the same parameters as the other mesh hoping that Salome will propagate the mesh in the T with the boundary layer, but when I generate the mesh, the boundary layer is disappeared on the cylinders. No way to have it back. Here is the picture of the whole mesh:






and if I display only the mesh on the cylinders:






... the boundary layer is gone.


Am I missing something? Is it a limitation of Salome?


Thanks in advance

[Alczem]

Hey


I would proceed the other way around: start with the unstructured volume, and mesh it with boundary layers (by adding a hypothesis within the netgen settings). Tune your settings until you are satisfied with the look of your three connections towards the straights pipes. Then create submeshes and use "3D Extrusion" for each straight pipe with the starting face being the face connected to the T-junction, and the ending face the outlets/inlets.


This way, you will propagate the boundary layers of your T-junction.

[giorgianig]

Originally Posted by Alczem

Hey


I would proceed the other way around: start with the unstructured volume, and mesh it with boundary layers (by adding a hypothesis within the netgen settings). Tune your settings until you are satisfied with the look of your three connections towards the straights pipes. Then create submeshes and use "3D Extrusion" for each straight pipe with the starting face being the face connected to the T-junction, and the ending face the outlets/inlets.


This way, you will propagate the boundary layers of your T-junction.

Hello, thanks for your answer. It doesn't work either. I created a submesh for the T, it generates it with boundary layers:





Then I created another submeshes for the straight pipes using 3d estrusion, when I generated it , the bounday layer is gone (it is still present on the T though, meaning the mesh is not conformal)






I know it seems trivial, but I turned around this problem for some days now, tried in every way possible, it doesn't work.

[Alczem]

Are you sure you extrude from the T-junction towards the extremities? It does work for me.

[giorgianig]

Originally Posted by Alczem

Are you sure you extrude from the T-junction towards the extremities? It does work for me.

Yes, I described the procedure in my previous answer. Maybe I am doing something wrong though, I don't know. Can we share files?

[Alczem]

You didn't mention explicitly which face you used as starting face for the 3D Extrusion, that's why I asked again. I didn't save the file, but I used Salome 9.10 if that makes any difference.

[giorgianig]

Originally Posted by Alczem

You didn't mention explicitly which face you used as starting face for the 3D Extrusion, that's why I asked again. I didn't save the file, but I used Salome 9.10 if that makes any difference.

I am on Salome 9.9 . When I do the 3D extrusion, I don't specify the face to start the extrusion. I use Extrusion 3D as 3D algorithm, Wire Discretization as 1D algorithm with a Local Length which specify the extrusion length. I don't see how to specify the face to extrude.



Here is my files on Dropbox if you want to take a look



https://www.dropbox.com/s/0v7ly43q5t...study.hdf?dl=0

[giorgianig]

Originally Posted by Alczem

You didn't mention explicitly which face you used as starting face for the 3D Extrusion, that's why I asked again. I didn't save the file, but I used Salome 9.10 if that makes any difference.

Sorry I uploaded the wrong file. It's actually quite the same, but the correct one is here:



https://www.dropbox.com/s/cj53nbrh5m...ified.hdf?dl=0

[giorgianig]

Originally Posted by Alczem

You didn't mention explicitly which face you used as starting face for the 3D Extrusion, that's why I asked again. I didn't save the file, but I used Salome 9.10 if that makes any difference.

I didn't have any hope, but I tried also with Salome 9.10, still no joy

[Alczem]

Hey


I took a look at your file, and the main issue you had is that the three straight sections are in one unique group. You have to define one group per pipe so that you can create one submesh per pipe. I attached a picture of what it looks like in Salome (the modified t-junction is the "junction_corr").


And you actually don't have to define a starting face when you extrude, my mistake it seems that Salome can tell which face to use for the sweep, but I created groups anyways, so ignore them.



Hope it helps!

[giorgianig]

Originally Posted by Alczem

Hey


I took a look at your file, and the main issue you had is that the three straight sections are in one unique group. You have to define one group per pipe so that you can create one submesh per pipe. I attached a picture of what it looks like in Salome (the modified t-junction is the "junction_corr").


And you actually don't have to define a starting face when you extrude, my mistake it seems that Salome can tell which face to use for the sweep, but I created groups anyways, so ignore them.



Hope it helps!

Hello Alczem, yes indeed that helped a lot. The mesh generation now works as expected in this geometry.

Indeed, this was a simplified example, in the reality I have several straight pipes connected to Ts. I am wondering if having a straight pipe connected with 2 Ts at both end will still work with this procedure, as now the extrusion I constrained at both ends. Maybe chosing the priorities between section in a smart way...

I'll try it out, thanks for the help so far.

[giorgianig]

Well, it actually generates a mesh with boundary layers, but every time I generate a mesh of a T attached to a pipe that I already meshed, the mesh seems not to be conformal... when I try to export it to OpenFoam, some default patches are generated.
So all in all the mesh is not valid again.