Instabilities of flow in a collapsed tube

In a previous paper (Jensen & Pedley 1989) a model was analysed describing the effects of longitudinal wall tension and energy loss through flow separation on the existence and nature of steady flow in a finite length of externally pressurized, elastic-walled tube. The stability of these steady flows to small time-dependent perturbations is now determined. A linear analysis shows that the tube may be unstable to at least three different modes of oscillation, with frequencies in distinct bands, depending on the governing parameters; neutral stability curves for each mode are calculated. The motion of the separation point at a construction in the tube appears to play an important role in the mechanism of these oscillations. A weakly nonlinear analysis is used to examine the instabilities in a neighbourhood of their neutral curves and to investigate mode interactions. The existence of multiple independent oscillations indicates that very complex dynamical behaviour may occur.