Scaling of the turbulent boundary layer subjected to an adverse pressure gradient

Although the concept of the boundary layer celebrates its 107th birthday in 2011, many fundamental important questions for modeling purposes are still not answered satisfactorily and are still debated. For instance, what is the layer-structure of turbulent boundary layers (TBLs)? What are the pertinent length and velocity scales for each region? What type of overlap layer or layers exists, if any? The lack of satisfactory answers is especially flagrant for the type of turbulent boundary layers most often encountered in applications: non-equilibrium TBLs. The focus of this work is talking and understanding more about different layers in TBLs. In other words, this paper revisits the issue of scaling of TBLs.