Laser Doppler Measurement of Local Flow Field in Collapsible Tube during Self-Excited Oscillation

The local velocity field in a self-excited oscillating flow through a collapsible tube has been precisely measured using a fiber optic laser Doppler velocimeter. Velocity distributions along the tube axis and across the tube cross section were measured. Time-varying flow rate at downstream end of the tube and pressure drop in the tube were also measured simultaneously. The following results were obtained:In the vicinity of the most strongly collapsed portion fluid is pushed to the downstream and upstream sides and then sucked back into the distending portion as the tube wall collapses and then recovers during the oscillation, and therefore superposition of this back-and-forth fluid motion to the gently varying flow gives rise to a sharp dent at the peak of the velocity waveform at upstream and a very sharp peak of the velocity waveform at downstream. Sufficiently far upstream from the collapsed portion, flow velocity is not influenced by the wall motion.