  Castillo and George (Castillo, L. and George, W., AIAA J. 39, 41(2001))
developed a flow governing equation approach for describing the turbulent outer
boundary layer region. The approach was used to develop similarity criteria for
the mean velocity and Reynolds shear stress profiles. Using the criteria as a
guide, Castillo, George, and coworkers examined an extensive set of
experimental datasets and claim that most of these turbulent velocity boundary
layers appear to be similar boundary layers when scaled with the Zagarola and
Smits (Zagarola, M. and Smits, A., J. Fluid Mech. 373, 33(1998)) velocity
parameter. In the work herein it is shown that their success at showing scaled
profile similarity in many of those datasets is flawed due to a similarity
problem that occurs when one combines the defect profile and the Zagarola and
Smits type of velocity scaling parameter. The same problem has been identified
in other papers in the literature and may in fact be widespread. We conclude
that similarity of the turbulent velocity profile is not as prevalent as was
claimed by Castillo, George, and coworkers. The result has implications as to
the accepted paradigm of the scaling of the turbulent boundary layer.
