Forced and unforced flow through compliant tubes

Abstract

The behavior (wall deformation and motion) of two compliant tubes made of an elastomer material were experimentally examined being part of a hydraulic loop. The basic feature of the tubes was the nonlinear dependence of their compliance on transmural pressure. One of the tubes, with a thickness to tube diameter ratio h/D = 12.5% and length to tube ratio L/D = 8.75 was set to a periodic motion, when a peristaltic pump was used for flow generation, buckled non axisymmetrically with a frequency equal to that of the pump. Due to the large amplitude pressure pulsations induced by the pump, the transmural pressure took in each period both positive and negative values which caused a tube shrinkage and expansion with a maximum amplitude of 60% of the tube radius. Moreover, resonance phenomena appeared when the pump frequency coincided with the natural frequency of the hydraulic system. When a progressive cavity pump was used, the weak pressure pulsations induced by this pump caused mild tube pulsations (up to 1.6% of the tube radius) and only when the transmural pressure was varying in the plateau of the pressure versus cross-sectional area curve. In both the above two cases, pressure amplitudes differed between the entrance and the exit of the tube approximately two times. The other tube with h/D = 3.3% and same L/D exposed to a flow established by gravity performed self-sustained oscillations causing large amplitude pressure pulsations downstream of the tube, flow limitation and negative resistance phenomena for which details are presented.