free" region which he perceives to begin at about 10-15D. This characterization seems a misnomer, in that the shear behaves in a continuous fashion over all x/D studied, as can be seen from Fig. 1. What does happen is that the velocity defect—and hence the mean-flow velocity gradient du/dr—decays to a small value very rapidly. Since all eddy viscosity models are utilized to predict the shear in conjunction with a gradient transport model [see Eq. (2)], one can then question the applicability of any such model when the velocity gradient becomes small. However, the present model was developed based upon the axial behavior of the shear and the velocity defect, both of which show no discernible change in behavior over the complete range of the data. More precisely, the slope of the distribution of these quantities (i.e., the decay rate) shows no change in value over the range of the experiment. Thus, no distinct regimes can be logically identified. Further, the numerical prediction is in roughly equivalent agreement with the data over the complete range in x/D studied, so that clearly the region of applicability of the present model extends at least that far downstream.