Hi Dr Amine Thank you for your reply!
To avoid particles bigger than mesh cells, I just initially used very coarse mesh. Therefore, the velocity and solid volume distribution were not perfectly matching with experimental results but still catching up with most of the solid-liquid flow behaviours. I want to improve it for further investigations. Thus, I add very fine inflation layers at the wall but these layers trapped particles and affected my results. Thus, I tried to use UDF (the DPM_SCALAR_UPDATE macro I mentioned earlier) to keep particles away from the inflation layers. Although most of the particles were away from the wall, some of them still trapped. Do you have any suggestions on this issue?
Secondly, as you mentioned adding an interior DPM wall to the system, I am very interested in this idea! Could you please explain it a little bit more? I am wondering if it means creating two domains in the meshing procedure (I am using ICEM) and importing them into Fluent?