[dushechka]

Hello everybody!

I try to mesh unstructured grid of one channel of double-entry centrifugal pump. Faced with the fact that, when my global element seed size is under 23, I have bad elements and I can't get good prism layers in this place.

I can't understand what is wrong... And what I should do?

I have changed global element seed size (20,10,15)... I have meshed one prism layer and tried to split it in several? but i didn't help.

With global element seed size higher than 23 everything is good

[kad]

I do not know why this happens when global max size drops below 23, but maybe some general guidelines can help you. I assume that you have octree surface mesh and delaunay volume mesh.

The simplest point first. Make sure all surfaces are marked correctly for prism creation. Is the orange surface checked for prism generation? The prism layer seems to stop there in screenshot number 2.

As prisms are extruded from the surface mesh, start prism generation with a hight quality surface mesh. The best way to achieve this is to throw the octree volume mesh right away and smooth the remainig surface mesh. Especially laplacian smoothing is a good option here. I usually run alternating cycles with laplacian on/off. I give you a little example:

- set smoothing iterations to 10
- activate "laplacian smooting"
- set "up to value" near your worst quality value
- run smoother

- deactivate "laplacian smoothing"
- run again
- increase "up to value" by 0.1
- begin from the start

Do this until you reach "up to value" e.g. 0.8 or 0.9. In the last smoothing cycle use laplacian smoothing with high value for "up to value" e.g. 0.95. For the last "normal" smoothing iteration use a value for "up to value" that represents around 10-20% of your worst element quality e.g. 0.3. The idea behind this is to get a mesh that is mostly laplacian smoothed, which is good for creating prism. The standard smoother helps to get rid of the worst elements.

While smoothing disable the option "allow node merging". This option can cause structures like the one I marked in one of your screenshots. After smoothing the surface mesh do not touch it again. This means freeze all tri_3 elements in any further smoothing operations. Also set "number of surface smoothing steps" to 0 in prism global mesh setup.

You can try so called floating height for prism creation. For this set all global and local heights for prism mesh to 0. These heights are then adjusted according to the size of the underlying surface element. In general this process should be pretty robust. To prevent the prism colum to stop also set a very low value for "min prism quality" in global mesh setup. Further check the document "Simons tipps and tricks" in the sticky thread. Very good guideline for creating prism mesh.

[dushechka]

Kad, thank you for advice but it didn't help. Actually after smoothing, that you recommended, I didn't have very bad shells any more, but the situation with the prism layers is the same. I even tried to change the geometry of the channel in this place, but it didn't help me too.

[kad]

Do the checks give you any errors? Maybe you can share your geometry.

[dushechka]

Originally Posted by kad

Do the checks give you any errors? Maybe you can share your geometry.

No.
Everything seemed good.

The archive with project files is too big, I can't upload it. I can't even upload archive of the geometry in Parasolid binary (79 KB)