Pulsatile Flows and Wall Shear Stress in Human Aortic Arch Model

• Main Authors: Yu-Lin Tsai, 蔡育霖
• Other Authors: Rong-Fung Huang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/vzsswd

碩士 === 國立臺灣科技大學 === 機械工程系 === 95 === Pulsatile flow characteristics and evolution processes in a model simulating the aortic arch of human being is diagnosed by using the particle tracking flow visualization method (PTFV) and the particle image velocimeter (PIV). The aortic arch model is made of transparent Plexiglas U-tube with three main branches (brachiocephalic artery, left common carotid artery, and left subclavian artery). Water is used as the working fluid. Pulsatile flows simulating the output of a human heart beat is supplied by a “pulsatile blood pump”. The results of this study are obtained using a 72 strokes/minute (1.2 Hz) stroke rate, a 75 ml/stroke (5.4 L/minute) stroke volume, and a 35%/65% systole/diastole ratio, all of which simulate the general conditions of the human cardiovascular system. The Womersley parameter, Dean number, and time-averaged Reynolds number are measured as 12.94, 2493, and 3697, respectively. The temporal/spatial evolution processes of the flow pattern, velocity distribution, and wall shear stress during systolic and diastolic phases are presented and discussed. It is found that the flows evolve complicatedly into three dimensional structures during the processes of acceleration, deceleration, and reversing. During the systole phase, the boundary layer on the inner wall separates from the area near the turning arch to the descending thoracic aorta. The induced reverse flow has low speed and would increase the probability of plaque deposition. During the diastolic phase, strong reverse flow is produced in the arch. Measured shear stresses show low values around the branch junctions and particularly high values around the outer wall of ascending aorta and descending thoracic aorta. These results correlate with the widely accepted clinic observation that the vessel segments that appear to be at the highest risk for development of atherosclerosis are around the junctions of the three branches and the aneurysms are tentatively found around the outer wall of ascending aorta and descending thoracic aorta. The oscillatory flow separation and shear stress distribution are apparently the primary causes leading to the atheroma and dissection/aneurysm.