I had an axcelent experience working with the grop led by Hrvoje Jasak at the University of Zagreb. He is one of the original developers of OpenFOAM and his group is formed by some of the best cfd professionals I have met. I am not sure if this is a place were you can start your post doc but you could ask him and I think he will point you in th right direction.
I think the Postdoc mentor of you is way more important than the school you join. I can list the good CFD schools but if the professor does not let you blossom that would not help you. And again like a "little hole in the wall" you may find very strong mentors in CFD in the schools which are not very well-known for their CFD program.