Re-evaluation of Nikuradse's Experimental Data for Rough Pipes

Abstract

Re-evaluation is made of Nikuradse's experimental results for turbulent flow in pipes roughened with sand grains. Application of Coles law of wall and law of wake justifies the existence of a drag-reducing behavior of velocity profile for a limited range of Reynolds numbers, first observed by Nikuradse but left unexplained. It is also found that the drag reduction due to this behavior is nearly cancelled by the drag increase due to the decrease of wake component of velocity profile.