Some preliminary observations on transition in a pipe

Conventional and conditionally sampled hot- wire measurements were taken in a pipe at Reynolds numbers corresponding to the onset of turbulence. It was observed that the laminar velocity profile is distorted in an axisymmetric fashion with increasing Re. At Re greater than 4000 the increase of Re has no significant effect on the shape of the laminar velocity profile when turbulent slugs appear. Some gross characteristics of turbulent slugs were examined. It was found that a typical slug is symmetrical provided that it originates in the pipe and is not triggered by an obstacle at the inlet.