controlling mass flow at outlet

Submitted by jsams on Mon, 08/15/2016 - 09:10

Dear liggghts community,

I am studying the granular flow in a hopper like geometry where particles enter the domain at the top and leave it at the bottom at a defined outlet. I would like to be able to control the mass flow rate at the outlet in order to study the flow behaviour at different discharge rates.

My questions therefore are: Is there a way to control the mass flow at the outlet other than changing outlet size? Maybe by deleting particles from a specific area at a certain rate?

Also, in order to attain steady-state flow, I would like to re-insert the removed particles at the top at the same rate as they leave the domain at the bottom. What strategies to achieve this can you recommend? I have been able to measure the mass flow rate with fix massflow/mesh; is it possible to simultaneously read the mass flow at the outlet and set it as an input for the fix insert/rate region? Periodic boundary conditions are not an option in my case as the outlet is not located at the same coordinate as the inlet.

I would like to hear your opinion, any will be highly appreciated.

Kind regards, Joel

Forums:

Daniel Queteschiner | Tue, 08/16/2016 - 14:02

For deleting particles you may use the delete_atoms command (http://www.cfdem.com/media/DEM/docu/delete_atoms.html) in combination with the every option of the run command. Alternatively you may have a look at the fix evaporate command (which is only available in an older version though: https://github.com/CFDEMproject/LIGGGHTS-PUBLIC/blob/3.1.0/src/MISC/fix_...).

If you have a fixed mass deletion/outflow rate you could simply use the same rate in an fix insert/stream command.

Using the mass flow rate measured by fix massflow/mesh for any fix insert/* command requires quite a bit of coding.

jsams | Wed, 08/17/2016 - 09:51

Thank you, Daniel!

fix evaporate seems to do exactly what I wanted, as I can specify the number of deleted atoms. I wonder why it is no longer supported in the current version of liggghts...

msandli | Tue, 11/08/2016 - 21:07

to alter massflow without changing outlet geometry, you might try changing your gravity, or maybe just fix a force to all particles that you can later change (this makes sense if all your particles are identical in size/mass)