Hi, everyone,
I’ve encountered an intriguing issue while simulating a bubbling fluidized bed using MFIX-TFM. After achieving steady-state fluidization, at a certain moment, the solid phase is abruptly blown out of the bed by what seems to be a strong virtual airflow. This results in a noticeable decrease in the volume of solids within the bed. Initially, I suspected that this was due to too large a time step (adaptive steps ranging from 1e-3 to 1e-9), so I adjusted the range to 1e-4 to 1e-9. Unfortunately, this adjustment didn’t resolve the problem, and the same phenomenon occurred again.
As shown in the figure below, at 42.9s, the fluidization was still normal; however, by 43.1s, particles were suddenly expelled from the bed in large quantities. It’s worth noting that this case is a test for gas-solid two-phase flow simulation conducted before simulating the wall-to-bed heat transfer process. The mesh near one of the walls was refined, resulting in a maximum aspect ratio of 10. When performing the same calculations with a uniform grid, this issue did not appear.
What puzzles me most is why this numerical issue occurs after steady-state fluidization rather than earlier. How can this issue be addressed? If this problem arises from having too high an aspect ratio, does it mean that MFIX-TFM might not be suitable for simulating wall-to-bed heat transfer process? In literature, much higher aspect ratios are used due to mesh refinement near the walls.
Has anyone experienced a similar issue or have any insights on how to solve this? Any advice would be greatly appreciated.
Thank you in advance for your help!
mfix.dat (4.9 KB)
