[tankerp]

Dear Foamers....

Im having a problem adding layers to my geometry. The geometry is a series of pipes and am planning to perform multiphase internal flow simulations.

Attached is an image of the mesh at one of the corners. While the snapping process and layer addition seems fine in some regions, layers do not propogate along the 90 degree bends.

Any suggestions on how to remove this problem are welcome. I have spent a considerable amount of time trying to fix this problem by tweaking various parameters in SHM. This problem is now causing a serious delay to the entire project.

Attached is a snapshot of the mesh at the corners. Thanks in advance.

[me3840]

Your background mesh is not very isotropic. If you make it isotropic the layer generation on the smaller walls will work better.

[tankerp]

Thank you for replying. What do you mean by making the background more isotropic?

[piu58]

How do you make three nodes form two in a hex mesh? That is not an easy task. One solution is to put tringular elements in between. One of the solution is what you see in your corners.

I downt assume that your geometry is twisted (no isotropic).

[tankerp]

Hi Uwe,

When you say that the geometry is twisted, do you mean that the geometry can be twisted if the snapping process is incorrect or just the geometry itself is incorrect?

Btw, I have an update. Since Simscale uses snappyHexMesh, I tried meshing the geometry using the default settings in simscale. Again the same problem persists at the corners. Do you have any suggestions? Could it be the geometry?

About the Geometry, I generated it using the following steps:
1. Created the geometry in FreeCAD and exported the STL file to Salome.
2. Generated a 2D surface mesh using NetGen2D before importing to Snappy.

I hope it is not too much to ask for, but I have also attached the SnappyHexMeshDict in this post. Could anybody check on it for any suggestions/changes in the settings for snapping/layer addition?

[me3840]

Look at the size of the cells in the middle of the channel. They are long in one direction and short in another. They should be nearly identical in lengths. Snappy doesn't work very well with anisotropic meshes like the one you have; you need to modify the blockMesh.

[piu58]

Dear Krishnan,

your mesh seems to be simple enough for blockmesh. Make your own meshes! They are much better than generated ones.

In your case: Is ist really necessary to change the node structure at the corners? I would let it as ist is.

Denser node packing is not easy. In one direction you may use denser layer of nodes which is supported by blockmesh. But what do yo do in the other coordinate(s)? One solution is to insert a layer of triangular elements. If you do that in a region where the solution is not important for you, that is a way.

I give you another way with only hex elements. There ist a layer with slightly distort elements, that is unavoidable:

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