Experimental Studies of Transition to Turbulence in a Pipe

In his landmark paper of 1883, Reynolds addressed the question of why the fluid motion along a pipe changes from a laminar to a turbulent state at modest flow rates. His discoveries have remained a focus of hydrodynamic stability for the intervening 125 years, and the central puzzle of why the transition takes place at all remains unresolved. It is an enigma as all theoretical and numerical evidence suggests that the base state of fully developed flow, Hagen-Poiseuille flow, is linearly stable. The transition to turbulence is abrupt, mysterious, and largely dependent on the quality of the facility used in any experimental investigation. It is therefore not an example of transition via a sequence of instabilities or bifurcations in which considerable success has been achieved over the same period. Despite wide-ranging research activity that has uncovered many important pieces of the jigsaw, the central puzzle remains unresolved. The purpose of this review is to bring together the available experimental evidence and attempt to extract a set of accepted facts about this important problem.