Inductive Approach to Hydraulic Friction Factor

The writer proposes that: 1. The scientific approach to the nature of the friction factor, \If\N, for turbulent flow, must be inductive at present. That is, it must proceed via collection and correlation of measurable quantities related to \If\N without bias in favor of theories. 2. The postulate of a universal form for \If\N, and information to date, including especially engineering field observations on both rigid and mobile boundaries, suggest the dependence of \If\N on the square root of an equivalent relative roughness for all phases of boundary condition. The equivalent roughness height, though of the dimensions of length, may depend on fluid or fluid-sediment-complex properties.