The effect of wall motion on the velocity field inside a flexible tube with a pulsatile flow.

Internal pulsatile flows exhibit a cyclic behavior of the mean axial velocity. These flows appear in many industrial and natural applications. Of particular interest is a pulsatile flow inside a cardiovascular system where fluid is driven by periodic cardiac pressure. To mimic this flow in an elastic aorta, an experimental setup has been assembled consisting of a piston-cylinder assembly connected to a flexible silicone tube. The amplitude of cyclic pressure was varied by adjusting piston’s maximum speed. The wall of the tube expanded and contracted under the force exerted by the fluid. Time-Resolved Particle Image Velocimetry (TR-PIV) technique was used to acquire velocity data on the plane of a CW laser illumination sheet to observe the effect of wall motion on the flow. In the case of low-pressure amplitude, walls were nearly stationary, resulting in a velocity field similar to that observed in rigid tubes. For larger pressure amplitude, resulting in a noticeable wall motion, the formation vortical structures were observed in the velocity field. These vortical structures were responsible for large instantaneous velocity fluctuations even for relatively small wall motion.