Mechanical Engineering - Theses
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ItemNumerical investigation of hemodynamics in stenotic vessels( 2023-08)Stenosis refers to any condition in which a vessel becomes abnormally narrow, so the flow through it is restricted. It is associated with an obstruction of a blood vessel lumen resulting in physiologically abnormal hemodynamics in the vessel and further progression of the obstruction. The presence of stenosis results in an acceleration of the flow past it which is accompanied by a noticeable drop in pressure, while the flow upstream and downstream of the stenosis is commonly disturbed due to rapid change in the geometry of the stenosed vessel. Stenotic flows can occur in various physiological contexts, including atherosclerosis, vascular diseases, inflammation, congenital heart defects and etc. Understanding the hemodynamics of stenotic flows is important for diagnosing and monitoring various cardiovascular diseases, as well as for designing medical devices and improving treatment strategies, encompassing pharmaceutical interventions, stent procedures, and surgical interventions. The objective of this thesis is to conduct a series of numerical experiments on stenotic flows under different geometrical and flow conditions using the direct numerical simulation method. In the thesis, the hemodynamics are numerically investigated in surrogate models that mimic vessels and their connections in the presence of stenosis. The thesis explores different origins of stenosis formation, including atherosclerosis, inflammation, subsequent scar tissue formation, and thrombosis. As an example of stenosis arising from the buildup of atherosclerotic deposits on the inner walls of arteries, the thesis considers a surrogate model that mimics the left anterior descending artery (LAD) affected by stenosis. To investigate hemodynamics in the presence of stenosis caused by scar tissue formation, stenoses at anastomoses between the artificial conduit and vessels in the surrogate model of the total cavopulmonary connection (TCPC) are examined. Furthermore, the thesis focuses on platelet activation triggered by the extensional flow in a channel with a stenosis of a hyperbolic shape. The surrogate LAD model yielded results that included various hemodynamic indices. These indices have the potential to predict the advancement of coronary artery disease. The results showed that alterations in the axisymmetric configuration of the stenosis significantly affect both the flow within the stenosis and downstream, emphasizing the importance of considering the asymmetry of the stenosis in diagnostics to enhance accuracy. The findings of the surrogate TCPC model revealed that the hemodynamics within the model are highly responsive to alterations in conduit stenosis geometry and relative lung perfusion. The most physiologically detrimental scenario, characterized by reduced energy efficiency and heightened wall shear stress, is observed in a TCPC with diffuse conduit stenosis and highly uneven lung perfusion. Finally, a noticeable response of platelet activation to the increased extensional and compressional forces in the flow of a channel with a stenosis of a hyperbolic shape was observed at the entrance and exit of the stenosis. In summary, the thesis delves into the hemodynamic environment of the stenotic flows and gains insights into the flow physics associated with physiologically abnormal hemodynamic metrics. Such insights are crucial for assessing the clinical risks and implications faced by cardiovascular disease patients.