Pulsatile Flow in a Tapered U-Tube

An experimental investigation of pulsatile flow through a tapered 180 curved tube, i.e., a U-tube, was performed to study the blood flow in the aorta. The experiments were carried out in a U-tube with a curvature radius ratio of 3.5 and a 50 reduction in the cross-sectional area from the entrance to the exit of the curved section. Velocity measurements were conducted by a laser Doppler velocimetry (LDV) for a Womersley number of 10, a mean Dean number of 400 and a flow rate ratio of 1. Additionally, flow was visualized to qualitatively investigate the nature of the flow, complementing the quantitative LDV measurements. The velocity profiles for steady and pulsatile flows in the tapered U-tube were compared with the corresponding results in a U-tube having a uniform cross-sectional area. The striking effects of the tapering on the flow are exhibited in the axial velocity profiles in the section from the latter half of the bend to the downstream tangent immediately behind the bend exit. A depression in the velocity profile appears at a smaller turn angle  in the case of tapering, although the magnitude of the depression relative to the cross-sectional average velocity decreases. Near the bend exit, strong secondary-flow motion occurs, leading to a weak depression in the velocity profile in the downstream tangent immediately behind the bend exit. The value of , which indicates the uniformity in the velocity profile over the cross section, decreases with increasing , whereas it rapidly increases immediately behind the bend exit.