Outer-layer universality of the mean velocity profile in turbulent wall-bounded flows

This paper deals with discerning outer-layer universality in the mean velocity profiles of turbulent boundary layers. For that purpose we derive an objective criterion which generalizes the classical wall scaling, as well as the Rotta-Clauser and Zagarola-Smits scaling. Outer-layer universality in the present scaling clearly emerges at displacement thickness Reynolds number exceeding about 3000. We propose universal velocity distributions based on simple patched logarithmic/parabolic fitting functions, which are accurate to within less than 1%