I'm trying to model the flow through a baffled truncated-pyramid-shaped inlet (see attached).
I want to track the particles that could escape back out of the inlet. I've tried to setup the boundary conditions to allow for this, but what ends up happening is most of my particles end up leaking out before they even get far into the inlet.
What I was doing was setting the out gassing on the inlet (the larger side) and changing the opacity to less than 1 to allow the particles to travel backwards. I'd then would set the outlet (the smaller side) with a pumping value, and leave the side walls as diffuse reflections. When I do this I get 89% of my particles leaking out of the inlet.
Obviously, I'm going about this the wrong way by changing the opacity. Does any one have any recommendations on how I would track the particles that, after reflecting off of the sidewalls, escape out of the inlet?
I hope I understood the desired functionality of this system, if my reply below doesn't solve what you want to achieve, let me know.
I think the solution consists of two steps:
Forcing particles to go in the inlet (between the walls)
Tracking particles that come back
The first step is more difficult. I was about to suggest to create a buffer volume on the inlet side, which is filled with gas, then that gas can make it through the baffle. But then you wouldn't be able to distinguish buffer particles from those that come back.
Therefore, you have to force particles in between the walls:
Create injection facets that fit the holes between the walls (at the inlet side). For this, you can use the Vertex / Create polygon in order command: select vertices that sorround the hole in a continous way, that's hard to explain so I made this screen recording:
Make sure their normal vector faces inwards (use the Swap Normal command in the facet menu if needed)
Select Cosine desorption. You might want to use the desorption/area so the gas quantity scales with the facet area
Set their opacity to zero
That way, particles are forced in between the walls, but since the injector facets are transparent, they can come back.
Once they come back, you can create a target facet or a target volume on the inlet side to track them as you wish.
If you're stuck, share the geometry and I'll set up a working model.
Marton, thanks for your help. Yes, you understood the problem exactly.
I need to clarify one thing and then ask a question though.
Firstly, the model I've made is of the negative space or where the gas would flow (I modeled the solid potions as the "open" space). I'm assuming your advice doesn't change, but I'll just use the existing facet as an inlet and make another one in the same place as a target or vice versa.
Secondly, I followed your example from the video, but when I do this, it doesn't close the facet. See image below.
The facet is not closed, because by convention, you have to go the different direction on the inner loop than on the outer loop. In your screenshot, the correct order would be:
2, 1, 5, 7, 2, 16, 15, 14, 13, 16.
Modeling the negative space, as you did, has many advantages, as we discussed before. As you say, in this case you don't need to manually create facets, but you can use the front faces for desorption. Just create a target facet or a buffer volume on the sides for tracking.
Finally, with Roberto we're always eager to know who uses the codes - can I ask which institution are you from?
So I think I finally have a good idea as to what I'm doing thanks to your help. I decided for simplicity sake, for now, to model the "flow" in a pyramid. I created a target surface very close to the inlet that absorbs particles that contact (in order to simulate an escape); otherwise, they would continue to reflect and eventually go through the outlet. This target is 1-sided, normal pointing in the same direction as the inlet so that the inlet particles can pass through, and if particles go back towards it, it's opaque (if I understand the "sides" option).
What I'm running into now are peculiar results. I'm unexpectedly loosing about 88% of my particles. Same results with cosine degassing, but since my inlet will be colimated with the "flow" of particles, I've been mostly using uniform. So I wanted to ask if you wouldn't mind looking at my .geo file to see if my setup makes sense? (Right now my set degassing number is small but random until I get the model working correctly)
Strange, for me your setup works well: particles are created at the inlet front and they either make it to the other side or get caught by your target facet:
(Blue dots are desorptions, red are absorptions).
You're also correct that one-sided facets are transparent from their back.
What exactly do you mean by "losing" 88% of particles? Are they leaking out?
I would do either of two modifications, though:
You could use the desorptions facets (inlet entrance) as targets, by setting a texture on them: test_pyramid_change1.zip
Or create a tager buffer volume, which could sum all returning particles from the different holes (for your original geometry): test_pyramid_target_buffer.zip
Thanks for taking a look. So what I mean by "losing", is that 88% of the particle absorptions occur back at the inlet. I'd would've expected more absorptions at the outlet or at least 50/50. But if my setup is correct, then I guess my design is ineffective at capturing the particles.
I'll take a look at those modifications. Thanks for passing those along.
