Dear Robert and Dr. Amine,

There are two theories that I have about this problem that I'd like to share with you and ask your opinion about:
1- I know that DPM tracks the particle trajectories point-wise and doesn't consider the diameter of the particle and updates the particle path by integrating F=ma for each particle in each time step. According to the model, if the center of a particle comes in contact with a wall cell, that particle will be considered trapped and will be eliminated from the domain (please correct me if I'm wrong).

Having said that, I may need a higher mesh resolution (larger number of cells) on my walls and close to the walls to better capture the wall geometry curvatures and therefore particle paths close to the walls.  As a reminder, my wires are 0.05 mm in diameter and my finest mesh size around the walls was 4e-6 m. According to the two photos that I sent as a reply to Robert on June 25, 2022, at 7:01 am, you can see that particles may follow different paths in case of different mesh resolutions close to the walls. It is noteworthy that I already have 7 inflation layers and based on velocity vectors close to the walls, I already have more than 10 nodes in my boundary layer and also my y+ value is about 0.015.

On the other side, as you can see in the post on June 27, 2022 at 8:30 pm as a reply to Dr. Amine, DPM results change even when I keep the mesh size around the walls constant and change the mesh size up/downstream only. It leads me to my second theory that:

2- the flow (velocity and pressure field) may actually not be fully resolved. As described earlier, I see an identical trend of the Z-velocity plot on a line drawn parallel to the flow direction (please refer to the following images). However, when I report Z-velocity on a specific point in the domain, I see up to a 10% difference in z-velocity for different mesh resolutions. These local differences may change the particle path since it will appear in the drag force on the particle in F=ma.

If this is the reason for my issue and I still need to decrease my mesh element size, what is a better criterion to check whether the flow parameters are fully resolved?