Experiments on transition to turbulence in a constant-acceleration pipe flow

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Experiments were conducted to study transition to turbulence in pipe flows started from rest with a linear increase in mean velocity. The data were taken at the Unsteady Flow Loop Facility at the Naval Underwater System Center, using a 5-cm diameter pipe 30 meters long. 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 was programmed to produce nearly constant mean flow accelerations, a, from 2 to 12 m/s2. In each of 37 runs, the time of transition to turbulence was the same throughout the pipe to within ±30 ms, indicating a global instability. As acceleration increased, the transition Reynolds number ReD increased monotonically from 2 × 105 to 5 × 105. Other dimensionless transition parameters are also presented, the simplest and most effective of which is T* ≈ 400±10 percent for the present experiments, where T* = tlr (a2/v)1/3 and v is kinematic viscosity. © 1989 by ASME.

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Journal of Fluids Engineering, Transactions of the ASME