A STUDY OF PULSATILE FLOW PHENOMENA WITH COMPUTATIONAL FLUID DYNAMICS APPROACH

Abstract

Cardiovascular disease (CVD) with the occurrence of plaque formation and sinus development related to stenosed and dilated area vasculatures is a chronic disease and has attracted wide attention among researchers because of its significant effect all over the world by leading to heart attack or stroke. Coronary and carotid arteries and their bifurcations are considered an enthusiastic research area for the pulsatile nature of blood flow. Numerical simulation of the considered left coronary artery has been studied in two-dimensional (2D) stenotic and three-dimensional (3D) geometric models of bifurcation for pulsatile blood flow to better understand the physical mechanism assuming fluid as Newtonian and non-Newtonian characteristics. The computational fluid dynamics (CFD) approach is incorporated in COMSOL Multiphysics with a satisfactory validation. This research indicates an extensive recirculation zone in Newtonian fluid as compared to that in the non-Newtonian rheological model, and hemodynamic parameters like shear stress can be considered a cabalistic factor in the commencement of arterial diseases. Computed hemodynamic parameters such as time-averaged wall shear stress (TAWSS), oscillatory shearing index (OSI), and relative residence time (RRT) are also able to make the difference between Newtonian and non-Newtonian fluids by forming atherosclerotic development variations. Elevated shear stress at the fibrous cap is investigated higher for a shear-thinning fluid. The present investigation also concentrates on the evaluations of the lesion of diagnostic concern on the basis of the diagnostic parameter’s critical values and investigates that the results are affected by the stenosis and rheological model. In 3D bifurcation geometry, the backflow region with a reduction of WSS is investigated computationally at the outer wall of the daughter vessel due to the noticeably low shear rate. The non-Newtonian importance factor (IFc) for the 3D left coronary artery bifurcation model decreases with an increase in bifurcation angle, and the smallest bifurcation angle generates the least time-averaged inlet pressure. Results further concentrate that the flow separation length reduces with developing bifurcation angle in bifurcated geometry. Computational simulation significantly furthermore elucidates that the non-Newtonian blood flow model incorporating hemodynamic and diagnostic parameters has great impacts on instantaneous flow systems. The transient numerical computational approach of fluid-structure interaction (FSI) has been modeled for an atherosclerotic fibrous plaque in a 2D carotid vasculature under the pressure action of normal and hypertension to detect the interactive effect of anatomical blood flow dynamics, the v properties of wall mechanics and pressure conditions on hemodynamics. A significant contribution of the present research on von Mises stress is that its magnitude has increased in HBP compared to that in NBP. The investigated results intend to expose that the variety of wall displacement and separation length occur due to the effect of pressure conditions in the flexible wall model. The TAWSS, OSI and RRT indicate the atherosclerotic thrombus deposition in generating potential risk parameters has a sequentially reduced separation length with an increase of mechanical elastic modulus. The results indicate the influence of elastic modulus on the increased value of the time averaged wall pressure gradient (TAWPG) and the time-averaged pressure drop in which maximum pressure drop is identified for NBP. The findings also illustrate that physiological hypertension gives a greater deformation gradient and stress tensor regarding the development of atherosclerosis. Time-dependent FSI computation of 3D patient data-based carotid geometry has been carried out in an idealized symmetric bifurcating vessel to show the effects of various sinus shapes on atherosclerotic plaque development. The significant impact of the variety of sinus shapes is offered in graphs and contours. In contrast to ellipsoidal and triangular sinuses, the current study shows that the trapezoidal sinus, which is prone to atherosclerosis, exhibits significant recirculation at both bifurcation walls. Based on simulation results, the inner wall of the trapezoidal sinus has a TAWSS that is 1.07 and 1.17 times greater than that of the ellipsoidal and triangular sinuses respectively. The present results demonstrate that the trapezoidal sinus has a larger pressure drop at the bifurcation point. The mass flow rate ratio for the ellipsoidal shape increases by 18% and 27% for that of trapezoidal and triangular shapes respectively. This research also indicates that a trapezoidal sinus of a human being is more susceptible to atherosclerotic plaque progression and development, leading to endothelial dysfunction, and its impact can be used in various biomedical sectors.