Laser-Doppler measurements of velocities just downstream of a collapsible tube during flow-induced oscillations

The flow field less than one diameter downstream of the end of a collapsibl e tube executing self-excited oscillations was examined using a two-compone nt fiber-optic laser-Doppler anemometer The time-averaged Reynolds number o f the flow was 11,000. With the tube oscillating periodically, results obta ined during many cycles of oscillation were combined to yield surface plots of the axial component over the cross section at 16 phases of the cycle. B y combining measurements obtained with the laser probe in two different ori entations, secondary flow vectors over the cross section were likewise cons tructed for 16 phases. The measurements showed strongly phasic turbulence i ntensity, with the phase of high intensity coinciding with the time of maxi mal tube collapse. Reverse flow occurred during much of the cycle, at place s in the cross section that agree with our previous observations of laminar and turbulent steady flow through a rigid simulated collapsed tube.