ABSTRACT
Now the velocity traverses of Nikuradse indicated that a suitable value for k was 0-4. Substituting this value and converting to common logarithms:
t w - V = 5,75 ! D (518) v, 6 2y
This is known as the velocity-deficiency (t’max — v) equation and is applicable to both smooth and rough pipes. As depicted in Fig. 5.5, the equation governs the relationship between r max and v. Unless either the maximum or wall velocity is known it does not of itself provide
sufficient information to enable the actual velocities across the section to be determined. The logarithmic form of the equation does, however, indicate that the velocity gradient is much steeper adjacent to the walls than in the central portion of the pipe.
