Meshing and convergence
 

I am carrying out a study on Ahmed's body in order to validate another study on external flow.

With a coarser mesh, I obtain satisfactory values, in addition to convergence. But I need greater precision.

Therefore, I was working on refining the mesh, calculating the size of the thickness of the first boundary layer and the Y+.

However, I find it difficult to obtain convergence of results when I refine the mesh. The residual graphs fluctuate a lot, as do the results for Cd and Cl.

Therefore, I would like to know how I can overcome this problem in order to achieve a good quality mesh and convergence of results.

Another issue is that, when I refine the mesh to the calculated values of the initial boundary layer thickness, there are very small cells, making it difficult to achieve good orthogonal quality of the mesh.

If anyone can help, I would greatly appreciate it.