Learning Forum

[Chris_g]

Hi,

I am trying to simulate a circulating fluidized bed with the DDPM model. I only model the riser, so I want to recirculate the particles that exit at the top back to the bottom of the domain. To achieve this I use a Volume injection to generate the initial particles and the Reinject boundary condition on the outlet. I have a "Reinjection Only" Surface-Injection on a plane on the Wall of the domain to reinsert the particle into the domain. This works fine when using the DPM model but when I activate DDPM and set the Discrete Phase Domain for the initial injection, it doesn't work anymore. That is, the simulation runs fine, but particles that leave through the outlet just disappear, so they don't appear back in the domain. In the console the "number tracked" decreases, but there are no messages like "escaped". If I print a "DPM Summary" the particles are identified as "Reinject" as would be expected, the only problem being that they are not actually reinjected.

Does the Reinject boundary work at all with DDPM, and if so what am I missing?

Thanks for the help!

[Rob]

Looking at the reinjection panel it's not got a selection box to tie it to the granular phase so the option may not be available. 

[Chris_g]

I' d assume it is linked to the granular phase through the injection, through the "Discrete Phase Domain". However, if this doesn't work, is there any chance of it working with a "DEFINE_BC" UDF, identifying the particle, moving it and setting PATH_REINJECT, or is this the sa,e thing fluent already tries to do?

[Rob]

When I checked the reinjection injection didn't have a connection to the phase domain. Can you show me what you're setting? 

If you write an injection UDF to reinject particles it should work as you'd be adding "new" particles rather than using the reinject function. 

[Chris_g]

Basically three places are relevant in my opinion. First picture is the boundary condition, where I set "reinject" and specify the injection to reinject the particles. All particles moving through the boundary should be treated that way if I understand correctly. Second picture is the initial injection that creates the particles in the domain. The it is linked to the phase "phase-2". Third picture is the injection to reinject the particles, which only specifies the new position and velocity.

 

So you're saying if I use a UDF I should use "DEFINE_DPM_INJECTION_INIT" instead of "DEFINE_DPM_BC"? I was thinking using the latter and doing it similar to example 5 in the UDF guide-

[Rob]

Check the definitions, I think the latter is to trap/escape/reflect particles. 

If you look at the "recycle" definition there's no Discrete Phase Domain when you turn on reinjection. I'm hoping the people who wrote the code are back in next week so I can check what the options are. 

[Chris_g]

Now I understand what you're telling me. If I deactivate "Reinjection only" and set "Total Flow Rate" to 0, I get the same behaviour in DPM but also have the option to select a granular phase. However, with DDPM this still doesn't work, the particles still disappear.

[Rob]

What I'm saying is the Reinjection option doesn't seem to link to the Phase Domain: the two people I need to talk to are away (half of Europe is off for a couple of days) so once they're back I may know more. 

[Chris_g]

Hi Rob, did you have a chance to clarify with your colleagues yet?

[Rob]

Apparently it should work, and did during testing. The reinjection should inherit the injection ID data from the particles, so should then pick up the Eulerian phase.