Grid independence and prismatic layer, a doubt
 

Hi all, this is a question for you

In order to achieve grid independence, of a 2D air flux over an airfoil, it has been told me that fixing the prismatic layer in the process of grid refinement is a good rule for maintaing the y+ value quite constant passing from a mesh to a sucessive one more fine.
I'm using k-e standard with wall functions then y+ have to stay in the range 30-100; but i see that it do change in the refinement exiting the correct range so i have must operate in the prismatic layer if i want restablish correct y+.
So which is the correct procedure?
Fixing the layer and let y+ exiting correct range or change the prismatic layer changing the starting pattern in the refinement process?