Fluid structure interaction study in model abdominal aortic aneurysms: Influence of shape and wall motion

摘要

Aneurysms are bulges in arteries which reflect unhealthy state of conduit in which blood is flowing. In the aorta, they are typically found in the abdominal region as well as thoracic region. Understanding the rupture risk of these vessels is critical to preventing failure and fatalities. In the current clinical practice, treatment modalities are initiated, when the out-pouching exceeds maximum diameter (D-max). However this approach is very crude as it does not account for the fluid mechanical forces and the attendant stresses. Since it is medically and ethically not possible to follow the patients to study the rupture risk potential, fluid structure interaction (FSI) modelling would be an apt tool to develop adequate understanding on various hemodynamic parameters. On the other hand, performing patient-specific studies would demand adequate lead time and they are computationally expensive as well. In the present study, the shape of the aneurysm and its interaction with the flowing fluid are accounted through the shape indices to study the FSI effects on the hemodynamic parameters. Numerical simulation of Newtonian flow through five axi-symmetric geometries with different shape indices coupled with a linear elastic vessel wall model is considered. From these simulations, it was observed that (D-max) to height ratio (DHr) is the most significant shape index which influences the variation of all hemodynamic parameters, which makes it a potential candidate for predicting rupture risk. Wall acceleration due to pulsatile flow was found to cause the onset of re-circulation zones at the centre of the aneurysm during early systole and the temporal deceleration resulted in the generation of near wall eddying structures during late diastole. Investigation of turbulence carried out with k-omega Shear Stress transport turbulence model, predicts a turbulence intensity of greater than 1.5% in the diseased segment as well as the distal end of the aneurysm.