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 a cross the tube cross section were measured. Time-varying flow rate at downstream end of the tube and pressure drop in the tube were also mea sured simultaneously. The following results were obtained: In the vici nity of the most strongly collapsed portion fluid is pushed to the dow nstream and upstream sides and then sucked back into the distending po rtion as the tube wall collapses and then recovers during the oscillat ion, and therefore superposition of this back-and-forth fluid motion t o the gently varying flow gives rise to a sharp dent at the peak of th e velocity waveform at upstream and a very sharp peak of the velocity waveform at downstream. Sufficiently far upstream from the collapsed p ortion, flow velocity is not influenced by the wall motion.