Trapezoidal blockMesh
 

I remember having seen an aircraft aerodynamics project where the team set an initial trapezoidal blockMesh shape so the turbulences which spread at the back follow more or less the block cells pattern and not crossing the cells like in the case of straight block.

Do you think this approach really makes a difference for convergence?
Is it is so, can we set a slip condition on the sides which are not parallel any more to the inlet flow direction?

Thanks!