TRANSITION FROM LAMINAR TO TURBULENT FLOW DURING UNSTEADY FLOW IN A SMOOTH PIPE

A study of flow establishment in a pipe was performed with a smooth straight circular pipe which was horizontally aligned. It was concluded that in the transition from laminar to turbulent flow in a pipe the effects of free- stream turbulence can be avoided entirely with a temporally expanding boundary layer. The transition occurs in spots. The magnitudes of the laminar boundary layer Reynolds number at turbulence inception was in reasonable agreement with the theoretical values determined for Blasius flow over a flat plate. The downstream movement of a turbulent zone into a laminar zone is that of physical transport. The regions of laminar and turbulent now in a pipe can be defined from the piezometric-head lines. With a systematic variation of boundary-layer parameters, the presence or absence of boundary-layer transition at the pipe junctions was found to be in qualitative agreement with the laminar boundary- laver stability theory. (J.S.R.)