[highpressure]

Hello everyone,


I am encountering some difficulties with snappyHexMesh and would appreciate your help. I am working on a CFD simulation involving a cylinder with a three-blade geometry inside. I have attached some screenshots of my current mesh, as well as a reference image from a thesis showing the desired mesh refinement.

1. Refinement in the Cylinder: I am trying to achieve a more refined and structured mesh inside the cylinder, similar to what you can see in the reference image of the three-blade geometry (attached file from a thesis). However, I am not satisfied with the current result in my mesh and am unsure about the exact parameters to adjust in the snappyHexMesh configuration file to obtain a finer and more uniform mesh around the blades.
2. Improvement of Layers: As you can see in the screenshots of the layers, I am uncertain about the quality of these layers for a CFD simulation. Can you give me your opinion on the acceptability of these layers and any advice on how to improve them?

Here the attached files:

• Reference Image (desired mesh): Screenshot of the desired mesh and the corresponding snappyHexMesh file.
• My current mesh: Screenshots of my current mesh and my snappyHexMesh file.

Thank you in advance for your assistance !

Best regards,

[Yann]

Hello Ilyes,

It looks like you could add a bit of refinement on your blades and inside your rotating zone. So basically increase the refinement levels.

For instance for the blades

        savonius
        {
            level (5 5);
        }

And for the volume:

        refinementCylinder
        {
            mode inside;
            levels ((1e15 4));
        }

Regards,
Yann

[highpressure]

Hello Yann,


Thank you for your response. Attached is a screenshot of the mesh after applying your suggestions. It is still not uniform.


Is there a way to force SnappyHexMesh to generate hexahedrons only in a certain domain?


Does a mesh need to be "aesthetically pleasing"?


Thanks in advance,

[Yann]

Hello Ilyes,

The square pattern is a bit weird, I don't really see what could cause it. Could you share your snappyHexMeshDict and snappy log?

Originally Posted by highpressure

Is there a way to force SnappyHexMesh to generate hexahedrons only in a certain domain?

Does a mesh need to be "aesthetically pleasing"?

Not sure to understand your question. Snappy creates hex-dominant meshes, and split cells to refine mesh and snap it onto the geometry.

Please note the lines visible on your screenshot are only a matter of visualization in ParaView (see here for instance: do Squiggles in snappyHexMesh effect quality)
You can also uncheck the "decompose polyhedra" option when loading your case in ParaView. (cfMesh noisy mesh)

[highpressure]

Bonjour Yann,


Thank you for your answer.

Originally Posted by Yann

The square pattern is a bit weird, I don't really see what could cause it. Could you share your snappyHexMeshDict and snappy log?

I've attached the snappyHexMeshDict, snappy log, and case file. I think the blockMesh might be a significant factor. Any advice on the required refinement level would be appreciated.

Originally Posted by Yann

Not sure to understand your question. Snappy creates hex-dominant meshes, and split cells to refine mesh and snap it onto the geometry.

Please note the lines visible on your screenshot are only a matter of visualization in ParaView (see here for instance: do Squiggles in snappyHexMesh effect quality)
You can also uncheck the "decompose polyhedra" option when loading your case in ParaView. (cfMesh noisy mesh)

By "aesthetically pleasing," I meant a uniform mesh without visible lines. I tried your suggestions and removed the lines in ParaView ! but the square patterns remain.


Best,
Ilyes

[Yann]

Hello,

Snappy is reaching the cell number limit defined in the maxGlobalCells parameter in snappyHexMeshDict, as you can see in the log file:

Shell refinement iteration 3
----------------------------

No cells marked for refinement since reached limit 5000000.

This might be why you don't get a proper volume refinement with these square patterns. Try increasing the maxGlobalCells and maxLocalCells.

[highpressure]

Hello Yann,


It works fine ! Thanks a lot for your help.


Regards,