Incorrect zones with STL Geometry

MFiX How to
#1

Hello,

I have a rare problem with the analized zone in STL geometry, this is a rectangular spouted bed with a cone for mass flow in bottom inlet. The software selected the spouted bed’s outside zone and the air mass flow going to sideways. To solve the problem, I probe increasing the cells number, also include a rectangular inlet to avoid the triangular geometry issue and this no change the problem.

I make and export in .stl file (binary and text) the geometry with COMSOL, then I set the IC & BC. The picture illustrate the issue better.
Geometry_zone_problem
Empty_Bed_2D.mfx (13.8 KB)
bed_5_binary.stl (684 Bytes)

#2

Your STL normal vectors are not consistent (see attached). You need to go back into COMSOL and fix the normals so they points towards the fluid region.

Note that if the normals were consistently pointing in the wrong direction, you could flip them in the GUI (https://mfix.netl.doe.gov/doc/mfix/19.1.0/reference/faq.html#how-to-verify-flip-stl-file-facet-normals). That won’t be sufficient here because some normals are pointing in the right direction and some are pointing in the wrong direction.

You may also need to refine the mesh to resolve the bottom inlet.

normals
normals608×810 38.3 KB

#3

Hi Jeff, thank you very much for answering. Now I solve the normal vector’s issue in COMSOL and I “verify the flip STL file facet normals”.

I had made the STL figure with surface, then I made a mixture with surface and solids and finally I made a solid figure. The problem was the surface without thickness and only solid figure with thickness solve the issue.

The final figure is red and the normal vector are blue.

image
image358×631 12.8 KB