How to achieve intermittent cycling of particles

Hello, teachers. Sorry to bother you again. I would like to implement intermittent cycling of particles in the y-direction of the reactor using mfix, e.g. when 0<time≤1 s, particles cycle and when 1<time≤2s, particles stop cycling. I tried to add an internal stl-moving-surface and a y-cyclic BC and made the moving-surface appear at 1-2s, the particles realized intermittent cycling. However, the gas keeps cycling in the y-direction, which does not satisfy my needs. I then tried adding a impermeable-surface, which blocks both the gas and the particles, but I don’t know how to get it to open intermittently to allow the gas and particles to pass through, and the UDF written didn’t work. Can you give me some guidance on this, thanks! (155.1 KB)

  • On the fluid side: I think you need to set the flags (see set_flags.f) when you turn on/off the IS.
  • On the solids DEM side: Please take a looks at the 3d dem mixer example. Here you want to slowly move the IS so it doesn’t suddenly cut into particles, which will lead to excessive overlap and huge forces.

Thank you for your patience in replying. I have noticed a strange phenomenon in the last couple of days: I have set an impermeable surface and a y-cyclic boundary in case1 without external stl. The impermeable surface works and gas/particles can’t across the impermeable surface(please see fig.1). When I need particles to go through, I can modify stl_preproc_des_mod.f. This is good and flexible. But I used the same method in case 2 with external stl. I found that the impermeable surface only works for particles and not for gases(please see fig.2), which is the opposite of what I need, I want particles to pass through and gases not to pass through. What may be the cause? Thank you! (2.9 MB) (5.1 MB)

@jeff.dietiker @cgw Dear seniors, can you help me to find out why the impermeable surface of case2 does not isolate the gas? I’ve been pouring over it for a few days, but still no solution, and there are no experts around who use mfix. However, this function: impermeable surface keeps blocking the gas and passing the particles intermittently (I used usr0 and usr1_des refer to 3d dem mixer example, but it doesn’t seem to work) is very important to me, please guide me, thanks!

usr0.f (2.9 KB)
usr1_des.f (2.5 KB)

I’ve just modified the set_flags.f(see fig. 3), and it seems that the impermeable surface can prevent the gas to go through, although some of the cases may not work yet (I don’t know why), but it’s a welcome progress. The main problem now is how to get the impermeable surface to intermittently let particles go through.
set_flags.f (17.6 KB)

I found that when using DMP parallel calculations, the method of modifying the set_flags.f-file fails and the gas still goes through the impermeable surface. Help :sob: