Author(s): Balkrishna Shankar Chavan
Linked Author(s): Balkrishna Shankar Chavan
Keywords: Friction factor, turbulent flow, laminar flow, Reynolds number, unified equation
Abstract: Computation of head loss is required in design of water conductor systems, such as close conduit as well as open channel. Darcy Weisbach friction factor (f) plays a decisive role in designing size and shape of water conductor systems. Estimation of f has no simple solution as it is very sensitive to geometrical as well as hydraulic parameters involving implicitly related Reynolds number and relative roughness. Solution requires iterative steps to arrive at required accuracy. Many investigators proposed explicit equations for approximate estimation of friction factor. These equations have theoretical, semi-theoretical and empirical base. Solutions are for stated restricted conditions. A plot of Reynolds number vs. friction factor by Nikuradse is well known. There are several approximations to the Colebrook equation. Some of them are Wood, Swami-Jain, Churchill, Barr, Chen, Zigrang-Sylvester, Serghides, Yen, Barenblatt, McKeon, Morrison, Haaland and are briefly described. Equations proposed by researchers are applicable for stated flow conditions, underestimates friction for higher Reynolds number. Obtaining a formulation that would provide the friction coefficient with a higher accuracy and applicable to wide flow conditions is goal for present paper. Here, we seek to unify the results and to provide an explicit formula for f valid in all forms of flow viz. transition, smooth and turbulent limits. Therefore, a new equation based on published data from various journals is compiled and analyzed for arriving at unified equation. Field data collected over 25 years has been utilized to derive the equation. In present paper, proposed explicit equation removes anomaly of decreasing values of friction factor for higher Reynolds number values, which was pointed out by ASCE Task Force. At the end, simplified equation for practically useful area friction coefficient (Mannings n) is proposed
Year: 2017