Turbulent Pipe Flow and Why Moody Was Wrong

Alexander J. Smits

Department of Mechanical and Aerospace Engineering

Princeton University

The Moody Diagram has been used to estimate frictional losses in smooth and rough pipes since it was first proposed in 1944. Recent experiments at Princeton in fully-developed turbulent pipe flow have shown that many of the assumptions made in deriving this engineering guide are not correct. In particular, a detailed study of the velocity profile in a smooth pipe at very high Reynolds numbers has led to an improved correlation for the smooth pipe friction factor, and a careful examination of the behavior for rough surfaces demonstrates the shortcomings of the friction factor correlation used by Moody for transitionally rough surfaces.