Thank you very much for your answer. I have watched these videos. I understand that kw-sst is y+ insensitive and change the treatment according to mesh. I did not know this actually. 

By the way, when I refine the boundary layer by decreasing y+, polyhedral mesh exhibist skewness values that are greater than 1. Should I try to decrease skewness of these cells? I am unsure that quality check of polyhedral mesh is similar to tetra cells. Should I care about skewness for polyhedras?