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

Abstract

o investigate the causes of self-excited oscillations of collapsible tube flow, measurements of dynamic tube deformation were conducted using a laser displacement meter supported 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 a supercritical flow and subcritical flow occur alternately during oscillations. By contrast, a linearized lumped parameter model has been developed. The model demonstrates that slight supercritical flow leads to instability of the negative stiffness type and also suggests that negative dynamic resistance induces instability of the negative damping type. Although 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.