Pulsatile Flows in the Human Aortic Arch:Flow Diagnostics using Particle Image Velocimetry

• Main Authors: Tsung Fu Cheng, 鄭崇孚
• Other Authors: Rong Fung Huang
• Format: Others
• Language: zh-TW
• Published: 2005
• Online Access: http://ndltd.ncl.edu.tw/handle/06513985702879049517

碩士 === 國立臺灣科技大學 === 機械工程系 === 93 === Flow characteristics and evolution process in aortic arch model are diagnosed by using the particle tracking flow visualization method (PTFV) and the particle image velocimetry (PIV) over various Reynolds numbers and pulsating frequencies. The aortic arch is modeled by a transparent plexiglass U-tube. Three types of flows (steady, sinusoidally oscillating, and heat-beat-simulating pulsatile) flows are supplied to the aortic simulator. The Reynolds number ranges from 2183 to 4311 and the pulsating frequency ranges from 0.1 to 1.15 Hz. In terms of the Womersley number, it ranges from 3.91 to 13.27. The time-evolving flow patterns are obtained from the PTFV and the quantitative flow properties, e.g., the velocity vector maps, the streamline patterns, the axial and normal velocity distributions, and the shear-stress contours are derived from the PIV measurements. It is found that the flows evolved complicatedly into three dimensional structures during the processes of acceleration and deceleration. The normal impulse component developed in the flow in the regions around the up- and downstream turning arches of the outer tube-wall are relatively high. This implies that the aortic dissection would be occurring there most easily. The wall shear stress distributions in these two particular regions are lower than those in other regions. A vortical flow motion is found to evolve from the turning arch near the inner wall to the descending thoracic aorta during the systolic process. During the diastolic process, strong reversed flow is produced along the inner walls of curvature. The axial flow velocities in the region of the vortical flow motion, which is induced during the systolic process, are low so that platelet deposition attached on the inner wall becomes possible. This would promote the growth of the atherosclerotic lesions. Besides, the transport of oxygen and metabolites to and from the inner wall are not efficient due to the separation along the inner wall in descending thoracic aorta. Therefore, aortic dissection is conducted in these regions.