The average skin friction coefficient (nondimensional and positive), Cf , for a turbulent boundarylayer depends on the Reynolds number (nondimensional and positive), Re, asCf = (Re) , (9)where and are unknown constants (i.e., which do not depend on Re). Note that is a positivemultiplicative factor and is the exponent of Re. The above form would lead to a nonlinearregression problem. We thus define y = log(Cf ) and x = log(Re) such that now y may be expressedas y = Ymodel(x; ) withYmodel(x; ) = 0 + 1x