314 狭さく管内の拍動噴流に形成される渦輪の形成過程のPIVによる解析(S42-2 流れの可視化実験解析(2),S42 流れの可視化実験解析)  [in Japanese] 314 PIV Analysis of the Formation Process of the Vortex ring Induced by Pulsataile Jet Flow in a Stenosed Pipe  [in Japanese]

The effect of the pulsatile ratio, defined as the ratio of the mean flow rate to the flow rate amplitude of pulsatile flow, on the formation process of the vortex ring in a stenosed pipe is studied using PIV. Phase mean velocity vectors in a stenosed model with 50% diameter reduction are measured under a sinusoidal pulsatile flow condition (amplitude Reynolds number Re0=550 and Womersley number α=25.5). It is obtained that the vortex ring is formed out of the separated shear layer induced by pulsatile jet flow at a stenosed. The pulsatile ratio has effect on the thickness and separation timing of the shear layer and the strength of vorticity in the shear layer. These cause change of the process of vortex ring formation and the vortex circulation. In the case of high pulsatile ratio, the vortex ring is formed during increasing period of flow rate, propagated downstream with high velocity and decreased in a cycle. In the case of low pulsatile ratio, however, the vortex ring formation is occurred during decreasing period of flow rate and propagation is sustained for a few cycles with low velocity. It is expected that there is the specific pulsatile ratio that the circulation of vortex ring is maximum value.