I studied a manual of Ansys CFX about turbulence models and I came across the term "non equilibrium boundary layer". What does this term mean?
For the equilibrium boundary layer, the local skin friction coefficient is independent of two parameters, both the streamwise distance and the Reynolds number, based on the momentum thickness, and the boundary layer thickness is proportional to the streamwise distance. On the other hand, for the non-equilibrium boundary layer, the local skin friction coefficient depends on the above two parameters.
This is from here
PS: This seems self explanatory. Please comment if you think an explanation is required. I have highlighted the parameters in bold myself.