So, to have an even packing, first I ran the simulation with a no slip wall at the outlet so all the particles would settle under gravity and then I exported the particle output. Using the particle output I started a new simulation with the outlet of the hopper as pressure outlet so that the particles could leave the domain. But after I start the simulation the particles leave very slowly / do not leave at all. I would really appreciate any suggestions on how I can get normal flow of particles through the hopper outlet.
I have attached the required files for your reference.
I will try to look at that and see if it has any effect. This is the result I get while using the packing generated by the solver. I do not see this kind of flow when I try this approach. I will keep you posted if I find what works.
It’s possible that the particles are just getting stuck due to excessive friction. You might also want to investigate the effect of particle stiffness (Young’s modulus).
Also it seems that perhaps the initial “uneven” packing is not much of an issue, as soon as the simulation starts running the empty spaces in the top hopper fill up pretty quickly. So maybe this isn’t really a problem (?)
I changed the collision model from linear spring dashpot to Hertzian which gave me access to the Young’s modulus and I am using the values specified in the literature. It works well when I have the initial packing but still does not when I used particle input.
For this application, I am trying to model dense granualar flow where the solid packing fraction is 0.6. The uneven packing is causing a reduction in the packing fraction when I fill the entire column (see pictures attached below). The first one shows the uneven packing and the second one is the results I get from settling the particles using gravity.
I am planning to use an external STL geometry to see if that helps with uniform packing. I appreciate you taking a look at this.
I think the issue is coming from the way particles exit the outlet plane. We freeze the particle velocity once they overlap the outlet plane. Here the initial velocity is zero so it doesn’t accelerate.
We need to think of a better way of doing it. In the meantime, do a first run with the bottom plane (no slip wall) above y=-0.099m, and the second run with the pressure outlet at y=-0.099m. That way particles will have a little room to accelerate.
When I tried to place the wall above the outlet and run the simulation I got this error " Error from check_data\check_bc_geometry.f:350
Error 1100: Invalid location specified for BC 2.
X: -0.20000E-01, 0.20000E-01 I: 2, 11
Y: -0.80000E-01,-0.80000E-01 J: 5, 4
Z: -0.20000E-01, 0.20000E-01 K: 2, 11
Fatal error reported on one or more processes. The .LOG file
may contain additional information about the failure.
Error from check_data\check_bc_geometry.f:350
Error 1100: Invalid location specified for BC 2.
X: -0.20000E-01, 0.20000E-01 I: 2, 11
Y: -0.80000E-01,-0.80000E-01 J: 5, 4
Z: -0.20000E-01, 0.20000E-01 K: 2, 11
Fatal error reported on one or more processes. The .LOG file
may contain additional information about the failure."
So, to work around it I used a impermeable membrane. Let the particles settle and then took these positions and imported it into my simulation and that worked. Thank you so much for the suggestion. I really appreciate yours and @cgw 's quick response and help.
