| dc.description.abstract | The vortex dynamics in cardiovascular flows play an important role in imposing flow features and forces acting on blood cells. Proper modeling and analysis of vortex dynamics in cardiovascular flows can shed light on the underlying reasons for various cardiovascular diseases. Numerical simulations of cardiovascular flows are challenging because they involve complex geometries with contacting deformable bodies undergoing high deformations and require fluid-structure interaction (FSI) for realistic results. In this work, a numerical framework is developed to study vortex dynamics of cardiovascular flows with FSI such as artificial heart valves. It consists of a rotation-free, high-deformation, thin shell finite element (FE) framework based on Loop’s subdivision surfaces. In order to model the response of bio-prosthetic heart valves (BHVs), a nonlinear and anisotropic material model is implemented that accounts for membrane and bending responses with a Fungelastic model. A novel physic-based contact model is incorporated into the framework to prevent the inter-leaflet penetration of the BHV leaflets during the closing phase. A series of benchmark problems are performed to validate and verify the thin shell elements, the material model, and the contact modeling, separately. The FE framework is then coupled with overset curvilinear immersed boundary (overset-CURVIB) framework using FSI with under-relaxation and Aitkin acceleration technique. The FSI FE-CURVIB framework is validated against experimental results of an inverted flapping flag using large eddy simulation (LES) modeling. Before the investigation of the effects of different heart valves, in a simplified setup, the vortex dynamics and propagation of periodically generated vortex rings are studied. A scaling law based on cycle-averaged Reynolds number and non-dimensional period is proposed for the propagation of vortex rings to predict their location. To test the findings in cardiovascular flows, the vortex dynamics of two main categories of heart valves, i.e., bi-leaflet mechanical heart valve (BMHV) and BHV, are studied. First, the vortex dynamics of BMHVs and their effects on the platelet activation are studied in a left ventricle-aorta configuration, incorporating a beating left ventricle (LV). In this study, three different implantation orientations are compared for multiple cycles. The results show symmetrical leaflet kinematics during the opening, while significant cycle-to-cycle variations are observed for the closing phase, which are due to the presence of small-scale vortical structures. The results show that the proposed scaling law with good precision can predict the location of the mitral vortex ring in the LV be-fore the vortex breakdown. Furthermore, our results show that the valve orientation does not have a significant effect on the distribution of viscous shear stress and total platelet activation in the ascending aorta. Then, the kinematics, vortex dynamics, and platelet activation of a BHV are investigated. The comparison of the BHV leaflet kinematics of FSI and dynamic simulations shows significant differences in the opening phase of valves. The FSI results show a displacement starting from the belly and developing to the free edges due to the hydrodynamic pressure distribution, in stark contrast to dynamic results; however, the closing phase is relatively similar. The vortical structures in the straight aorta with the implanted BHV are visualized and studied for the complete cycle. The propagation of the complex three-lobed vortex ring during the opening phase was predicted using the scaling law with an acceptable margin. In addition to the previously observed vortex rings during the opening, two vortex rings during the closing phase are detected for the first time, due to the kinematics of the leaflets. In conclusion, while the results of different heart valves show high complexities in both structural and flow features, they illustrate similar physics/scaling in terms of the location and interaction of the vortical structures. | |
