Experiments on transition to turbulence in a constant- acceleration pipe flow
Abstract
Experiments were conducted to study transition to turbulence in pipe flows started from rest with a linear increase in mean velocity. 37 runs were carried out at the Unsteady Flow Loop Facility at the Naval Underwater Systems Centre, using a 30 m long, 5 cm diameter pipe. Instrumentation included static pressure, wall pressure and wall shear stress sensors, as well as a laser Doppler velocimeter and a transient flowmeter. A downstream control valve produced nearly constant mean flow accelerations. In all runs the time of transition to turbulence was the same throughout the pipe, indicating a global instability. As acceleration increased, the transition Reynolds number increased monotonically. Other dimensionless transition parameters are also presented. Results imply that transition time is nearly independent of pipe diameter. (from authors' abstract)