SimScale CAE Forum

CFD through a lattice structure

Hello! I am relatively new to CFD simulations, but am working on a project looking at fluid flow through lattice type structures. I am having a lot of trouble generating the meshes from the CAD geometries I am exporting from Autodesk Netfabb. I have little experience with CAD, so I am assuming some imprecision in my geometry is causing the mesh generation to fail.

The meshing error is “A multi-region mesh is being used in a single-region analysis type. Please make sure that all regions except for one have an advanced concept assigned to them.”

Since I want to simulate flow through the structure, I generated the flow volume by performing a boolean on a cylinder and a lattice structure (generated via the lattice commander tool in Autodesk). I exported this as a .stl to SimScale. I have pictures of the geometry attached below:

How would I determine where my mesh generation is failing, so that I can modify the CAD properly? Any help is appreciated.

Here is a google drive link to the .stl file I am using:

Hi @lattia,

After importing the geometry to SimScale, you should should have only one solid. Please check geometry import statistics. This solid is your simulation domain, being water or air left within cylinder (lattice itself removed). You can try to mesh it and in that case you should not see anymore message about ‘multi-region’.

However, STL format may be causing meshing problems, as the simulation domain become huge. You may be better off using different format (like Parasolid).

Moreover, I suggest to try first “standard mesh”, which is TET based (not HEX based), very coarse and automatic. That kind of fine structure will be not obvious to mesh in a simple manner, but at least TET based mesh should allow appropriate finesse after few trials.

Please give us the link to your SimScale project, when ready.,

Take care,



Hi @Retsam,
Thank you for your response.
I checked my geometry import statistics and I do have 2 solids, 1 being the “shell” of the lattice, and the other being the cylinder.

I understand this is thus more of a CAD-related question, but why is my .stl exporting from Autodesk Netfabb as 2 solids? I performed a boolean of the solid lattice and solid cylinder in Netfabb, and exported the resulting part into SimScale. Shouldn’t this yield a single part? If not, how would I limit it to only 1 part such that the solid is only the flow volume?

Here is the link to my project:

The geometry in question is titled “52 mm radius boolean.” I have other geometries in this project that are similar but I think this current geometry is the most useful one.


I tried a different strategy for part generation in Netfabb to yield 1 solid only, and am wondering if you can take a look at this part. I attempted to upload it to SimScale but encountered an error during upload.

The .stl can be accessed at this link:

Please, in SimScale, test the use of “Add Geometry operation”:

I could not diagnose the error for an upload of geometry: I’m also on customer side only.

I am able to add a geometry operation

Is there a specific geometry operation that would be of use here?

Yes: Extract flow volume…

I hope you are doing well.

I just shared a newer project with you that has an updated CAD design of only the flow volume, and is only a single solid. However, Simscale is unable to recognize the different faces on the top or bottom of my flow volume, so I am unable to set proper boundary conditions. If you have any advice on how to do resolve this issue, please let me know.

Please give me a link to your new project here. I will take a look.

Take care,


1 Like

Thank you very much.
Here is the link:

Your STL geometry has only one face [face2@solid1] to use for BC (there is no top, bottom, side or sides). This will not fly and you cannot assign inlet or outlet for flow.

Possibly it is linked to STL format, but I’m not sure.

I would suggest to make your lattice internal (not touching the sides or top / bottom of your geometry).

Take care,


1 Like