[andrenel]

Hi All,

I have been wandering around in the openFoam CFD space for a few months, trying to make sense of the process. At this point, I am lost and frustrated.

I am trying to simulate an inline gas filter. This filter consists of a housing and a pleated fabric filter. The fabric filter has 50 pleats of 0.23-inch depth. I simulate the porosity by cutting slots in the pleats with an open area equal to 40% of a pleats surface area.

Using Fusion 360, I create an stl file. I adjust the stl options until I am satisfied with the mesh. They look pretty good -- fairly uniform grid.

At this point, I use the snappyHexMesh GUI add-in for Blender and export the mesh files to the openFoam case. There I run a script that creates the block mesh, extracts the edges, and finally runs snappyHexMesh with the overwrite option. What was a fairly nice mesh has become a mess of horribly small cells when examined using paraView. The model I have has 7 components. I looks like the settings of the snappyHexMesh GUI bleed across components and effect one another.

A little more about what I am trying to do. I am trying to get the velocity of the flow so that I can calculate the flow rate (SCFH). I set the inlet and outlet pressures to fix values. I am using Imperial units.

One of the things I noticed yesterday was the with the units set to Imperial I had to put in a scaling factor to make the measured dimensions of the filter to come out right in Blender (Blunder?).

Anyhow, I am using icoFoam. What happens is that the Courant Numbers and the residuals increase rapidly and the simulation crashes with a floating point error. Not surprising since the mesh is so fine.

I am shooting for a Courant number equal to around 0.7, at a velocity of 10 m/s (394 in/s) with a cell length of around 0.006 m (0.25 in). This means the delta T should be 0.0004 seconds. Unfortunately, my cell length, after snappyHexMesh is way too small.

Finally, here are the questions:

1. Are there any recommendations for the settings in snappyHexMesh GUI. Most of the model is pretty course except for the pleated filter fabric.
I have tried to reduce if to a mesh surface but could not get is to Castelate.

2. Can I create a mesh in the CAD software by subtracting my filter assembly from a bar, taking the interior portion and using that in the icoFoam simulation?