  Correlations of friction factors are presented for the general case of purely
viscous non-Newtonian fluids without requiring a priori the adoption of a
rheological model. They are based on an empirical estimate of the shift in the
wall layer edge and the Kolmogorov point. The predictions of friction factors
have the same level of accuracy as those of the Dodge-Metzner correlation but
the visualisation is more compatible with measured velocity profiles. The
general correlations obtained can be used to easily retrieve correlations for
specific rheological models.
