Mesh Creation Input Questions

Using SimScale Fluid Flow / CFD
1

When creating a Mesh, one can choose “Hex Dominant (CFD Only)” which has much less inputs than the Parametric version. However, it seems as though you can add a few refinements but the help bubbles are a bit confusing. For example, for “Inflate Boundary Layer” under the “First Layer Thickness”, it isn’t clear what the units are. Plus, the help bubble talks about the “Final Layer Thickness”. So which is it?

Second, under “Surface Refinement” it shows units of “m” for the “Length field”. Is this really in meters or is it relative to the mesh size? The help bubbles talk about levels and not length. I though all refinement “Levels” where actually relative to the base mesh.

Third, under “Region Refinement” using internal, there is a “Length” field with units of “m”. I am familiar with the “Region Refinement” using parametric where the value is a “Level” but this is kind of confusing and there is no help bubble for that.

Thanks

2

Hi @mas985!

Discussing this with my colleagues. Will get back to you as soon as possible!

Best,

Jousef

3

Hi @mas985
thanks for reporting these. Let me try to clarify

  1. The help text is indeed incorrect. The thickness is for the first layer. The units are absent and this is correct because the thickness is relative (to the size of the cell).
  2. The help text is again incorrect. The hex-dominant (CFD) mesher has all lengths given in the unit of the project (i.e. meters in your case). We convert this in the back-end to a refinement level. The help text is outdated and we need to fix it.
  3. Same for region refinement, we decided on length semantics rather than level. The help is missing and we’ll add it in the same chunk.

Thanks for pointing these out! You’re helping us turn SimScale into a better product.
Johannes

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4

Regarding #1, is the first layer considered the layer closest to the wall? And is the thickness relative to the base cell layer or the cell layer that is at the wall prior to inflation?

Thanks

5

Hi @mas985!

The first layer is the one adjacent to the wall with the minimum layer thickness below which height layers will
automatically be collapsed. For the thickness which is defined by the expansion ratio you have:

\frac{\Delta \text{Second Layer}}{\Delta \text{First Layer}} = \frac{\Delta \text{Third Layer}}{\Delta \text{Second Layer}} = \frac{\Delta \text{Fourth Layer}}{\Delta \text{Third Layer}} \quad \text{and so on...}

Note: The thickness of the final layer is the ratio of the final layer height relative to the first layer.

Does that answer your question?

Best,

Jousef

6

The input for the first layer thickness is relative to another cell height. My question is which cell height? The base mesh cell height or the cell height of the cells that the inflation layer is replacing. After a couple of quick measurements, I believe it is the latter but I just wanted to confirm that.

Thanks

7

Hi @mas985!

That’s what I would have to check by myself - @1318980 & @Get_Barried, can you answer this?

Cheers!

Jousef

8

Hey @mas985, you are correct layering is done last in the order of things, so after refinements, snapping and quality, inflation then takes place relative to the refinement at the surface.

Best,
Darren

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