Relation of Pressure Wave Velocity to Self-Excited Oscillation of Collapsible Tube Flow.

Abstract

To investigate causes of self - excited oscillations of collapsible tube flow, measurements of dynamic tube deformation were conducted with a laser displacement meter carried on a pulse-motor stage together with an electromagnetic flow meter. The results have clarified that fluid velocity approaches pressure wave velocity, which is estimated from the tube law, at the throat around the stability boundaries and that supercritical flow and subcritical flow occur alternately during oscillations. On the other hand, a linearized lumped parameter model has been developed. The model explains that slight supercritical flow leads to jnstability of negative stiffness type and also suggests that dynamic negative resistance induces instability of negative damping type. Though the causes such as unsteady flow separation were not examined here, a self-excited oscillation caused by supercritical flow close to choking has been verified experimentally and theoretically.