Numerical analysis of physiological flow through an arterial bend with aneurysm

Abstract

Aneurysms are localized blood-filled balloon-like bulges which can occur in any blood vessel. The term coronary artery aneurysm refers to both diffuse, where arterial segments dilate more than 1.5 times of the largest diameter of a coronary artery and spherical or saccular dilation. Atherosclerosis is the main cause of these anomalies in adults and Kawasaki disease in children and adolescents. In this study, the simulation has been done for S shaped coronary artery with saccular aneurysm using physiological flow rate condition on the inlet boundary and a corresponding physiological pressure condition on the outlet boundary to precisely describe the cyclic nature of heart. In simulating blood flow, one important aspect is to accurately model blood as a fluid. As instantaneous shear rate varies from 0 to 1000s-1 over a cardiac cycle depending on circumstances, it is always beneficial to examine the non-Newtonian effect on physiological blood flows. Both Newtonian and non-Newtonian models have been compared in this study to justify the use of Non Newtonian model. Previous experimental investigations show a transition to turbulent flow occurring during the deceleration phase of the cardiac cycle. Moreover, Irregularities in flow geometry create flow separation, recirculation, reattachment and turbulence. Laminar and k − ω turbulence model have been compared to choose the k − ω turbulence model over Laminar model. Validation has been conducted using a simple 90o bend channel with a pulsatile velocity inlet boundary condition. Flow has been considered as Newtonian, Laminar, incompressible. This allows comparing the simulated results with the experimental investigation. Axial velocity profiles and secondary flow patterns have been compared and found in good agreement. Though Patient-specific models are attractive for understanding the specific blood flow dynamics in real human body, based on several studies, idealized model of S shaped curved coronary artery of diameter 3.5 mm with time-averaged Reynolds number of 150 has been analyzed in the present study for illustrating the relationship between geometric characteristics and inflow features at four different time periods of cardiac cycle. Temporal and spatial distribution of axial velocity profiles and secondary flow patterns have been analyzed. Wall shear stress (WSS) and Time averaged wall shear stress (TAWSS) have been found to have higher values in artery with aneurysm than healthy artery. At a fixed neck size the values of WSS and TAWSS remain more or less constant during the growth of aneurysm. But these values have been observed to change while changing the time periods of cardiac cycle. Maximum value of WSS has been observed to increase with the decrease of time period at minimum velocities of systolic and diastolic phase, but observed to decrease with the decrease of time period at maximum velocities of systolic and diastolic phase. Oscillatory Shear Index (OSI) varies between 0 and 0.5 depending on cyclic variation of WSS vector. But, OSI has been found to decrease with the decrease of time period. Relative Residence Time (RRT) has been checked and observed that spots of high RRT decrease with the decrease of time period.