Learning Forum

[reza121]

Good day, I hope you are doing well. 

I am trying to simulate particle deposition on wire screens using DPM in fluent. As we know, since fluent considers the particles as point particles, it doesn't take into account the interception mechanism for particle capture on the wires which happens when the particles come within one particle radius from the wires(please refer to the following photo). I found this paper that has created a "virtual surface" around the wires to account for the interception. this line is from the paper:

"In FLUENT, a “virtual surface” was created by building an Interior Boundary with the Surface function".

Later, to count the number of particles that had passed through that virtual surface, a sample report should be created for that surface (report>discrete phase>sample)

Based on the approach that I took, I was able to create a surface that is an offset of my screen at the desired distance by using surface>create>transform>iso distance and then selecting my screen geometry. The problem is that it only creates a surface and not an "interior boundary" as stated above. Consequently, I can not get a discrete phase sample report on that surface (it won't appear in the list). I believe that it should appear in the sample report list if I somehow get to define it as an interior boundary since I can see the interior-fluiddomain in the list (please refer to the last photo)

Would you please help me with creating the interior boundary in the right way?

Thanks in advance

 

[Rob]

Transform and the other tools in that menu are for post processing surfaces. If the near wall cell is bigger than the particle collisions are calculated as normal. If they're not, then read the definition of the DPM model. 

The offset surface needs to be created in the geometry stage, or use boundary adaption if you have inflation and a cell boundary in the right location. 

[reza121]

Thanks for your reply, Rob.

Would you please elaborate a little more how increasing the first cell height will result in the model accounting for interception too? You once said that particle trap on the walls won't be examined unless the particle is in the near-wall cell. However, even if my near-wall cell's height is 10 microns and I'm studying a 5 micron particle, the particle still has to hit the wall to be counted as trapped and it won't be trapped if it comes to a let's say 1 micron particle center to wall distance. (Or will it? Please correct me if I'm wrong). If the model doesn't trap the particles at the wall distances below the particle radius, there is a chance that the particle that should've been marked as trapped would flee away from the wire and it will cause an underprediction in the filter efficiency. 

That would be great if you could please send me the relevant fluent manual documents in this regard as I couldn't find them.

Thank you

[Rob]

From my understanding (and I'm a user not a developer). Once the particle enters the near wall cell collisions are checked, so for a 10micron cell a 5micron diameter particle will be tracked until it's 2.5microns from the surface. Then it collides. A 10 micron particle entering a 5micron cell will collide the moment it enters the near wall cell.