Requiring some help regarding tornado simulation
 

Hello everyone, hoping everyone is doing fine. I am trying to run a simulation for tornado in a cylinder (height 2.07 m and radius .4 m). As it is a tornado simulation I need to have very fine grid near the base of my cylinder as it is the surface of my tornado simulation. Some part of the wall of the cylinder is Velocity inlet (from the base to .41 m ). The rest of the wall is named sidewall and it is a free slip wall (no shear stress). the mesh size is uniform and it is 0.04 m. I am using SIMPLEC method with second order discriticization and skewness 2 was used. In order to get finer grid near base I adapted the grid so that Y+ value becomes below 1 near the base and I can use enhanced wall function . FYI I am using RSM model for my simulation. I also adapted the grid for velocity gradient (0.0002). The problem is order to adaptation at first I ran the simulation without enhanced wall treatment. But when i tried to change the wall treatment to enhanced wall treatment (after 3000-4000 iterations, when the Y+value becomes below 1) the simulation Diverges and show me some AMG solver error. Can anyone please help me regarding this problem. Another thin do I need to re initialize my problem once I adapted the grid or I can run my iteration from there. Thanks in advance for all your assistance.