Hi Experts,

I noticed that the terminal velocity of particles under similar conditions except for the length of the container using the cyclic boundary condition in the vertical axis gave significantly different results. I am thinking that the reason for this is that both the fluid and particles are recycled when they get to the bottom of the container, instead of maybe just the particles.

Is this assumption correct? Is there also a way to set only the particles to recycle and maybe apply pressure output for the fluid phase?

Please your thoughts and direction are highly solicited.

How dense is your system and do you see a plug pushing the gas down? The cyclic BCs recycle both fluid and solids, there is no built-in way to only recycle particles. Maybe you can turn off momentum equations for the gas phase. This will mimic particles dropping in stagnant air.

Thank you so much for your quick response, Sir. I observed that the gas continues to accelerate over time in the entire container. That was what informed my thought of the cyclic boundary condition being the reason. The density of the gas is 1.3 kg/m3.

If I turn off the gas phase momentum equation, will it not have effects on the influence of the fluid phase on terminal velocity as well as on granular pressure and temperature?

I will run simulations to check this, but in the meantime, your insight will be very helpful as usual.

Thank you!

I forgot to ask, are you actually applying a pressure drop? If you apply a pressure drop equal to the hydrostatic pressure (DP=rho_g x gravity x h) this should prevent the fluid from accelerating.

If you don’t solve the gas momentum equation, you will still have the drag acting on the particle.

Noted.

Thank you so much for your insight.

I will attempt these two solutions to see the one that works for me.