Problem with MFIX-DEM simulation in a bend with refined grid

[panm]

Hello everyone,

I am currently working on a simulation using MFIX-DEM to study the particle motion in a bend, I have encountered some issues during the simulation process.

Initially, I used a computational grid of 40x60x10, and MFIX provided results for both the flow field and particle motion, although the results were quite rough. When I attempted to refine the grid, specifically increasing the grid in the z-direction from 10 to 20, the simulation could not proceed. The error message indicated “dt < dt_min”.

I have checked the CFL number, and according to the grid size, time step, and inlet velocity, dt_min should satisfy the CFL condition. Even after reducing dt_min to 10^{-10}, the simulation still failed to run.

Could any experts provide suggestions on how I can successfully perform calculations with a finer grid? Below are the simulation parameters I used. Could you check if there is anything wrong with them?
bend_dem.zip (1.4 MB)

[jeff.dietiker]

Not sure it is a good idea to only refine in the z-direction, this will create high aspect ratio cells. Please try to increase the number of linear solver max iterations for pressure and momentum to see if it helps.