[Peter2010]

Hello. I am quite new in CFD and I'm going to mesh a radial flow pump with an unstructured grid. I have a general question concerning the creation of prism layers.
So I am wondering how large the whole prism-area should be to get a good mesh? (I'm using SST-Model with automatic wall function, so I found out that the boundary layer should be resolved with about 5...10 prism-layers and the value of y+ should be about 30 in my case.) But is it worse to make the whole prism-area much wider than the boundary layer? I think that the prism elements in general have a better quality than tet-elements... so why not creating as much prisms that reach pretty far into the inner flow? Is there a limit, or a general recommendation, for the width of the prism layers? Should they only be used for the region close to the wall? If true, why is it better to use tet-elements from a certain distance from the wall?

Thanks very mush for your help!