The Transition to and from Turbulence in a pipe

A discussion of experimental investigations of the stability of flow along a pipe will be given. The transition to turbulence is catastrophic when a well--defined amplitude of injected perturbations is exceeded. The stability threshold scales inversely proportional to the Reynolds number, $Re$, with a sharp cut off at low $Re$ values. On the other hand, the decay from the turbulent state exhibits systematic exponential behavior with diverging timescales which are indicative of critical behavior. The long transients contain spatio-temporal coherence which suggest connections with recent theoretical developments.