Critical Reynolds Number in Constant-Acceleration Pipe Flow From an Initial Steady Laminar State

The transition to turbulence in a constant-acceleration pipe flow from an initial laminar state was investigated in a custom-made apparatus permitting visual access to the water flow in the pipe. The apparatus allowed both laser Doppler velocimetry measurements and flow visualization using a tracer. The experiment was carried out by accelerating the flow from a steady laminar state to a steady turbulent state. The relation between the critical Reynolds number for transition to turbulence and the acceleration was found to be similar to that in a constant-acceleration pipe flow started from rest. In addition, with increased acceleration, the turbulent transition was found to be delayed to higher Reynolds numbers using flow visualization with simultaneous laser Doppler velocimetry measurements.