Computational Fluid Dynamics Modelling and Simulation for Angular Neck of Abdominal Aortic Aneurysm

Abstract

An abdominal aortic aneurysm (AAA) is one of serious pathologies of cardiovascular diseases. This disease is defined as a localized expansion of the abdominal aorta. A normal size of a healthy artery is estimated between 1.5 and 2.4 cm based on several categories such as age, gender, and body weight. The rupture occurs if there is an increase in the aneurysm sac diameter up to 3.0 cm or if the aneurysm keeps growing or is not treated. Proximal neck angulation of AAA is believed to influence the hemodynamic changes and wall shear stress (WSS) within AAAS. This study aimed to investigate the impact of AAA angulation on the hemodynamic parameters such as flow behaviours, wall shear stress (WSS) and pressure in two different models; 3D constructed models and patient-specific geometry of angulated neck of AAA by implementing computational fluid dynamics (CFD). In this work, the 3D constructed angulated neck of AAA models were constructed using SolidWorks software, while the patient-specific AAA geometry was reconstructed from computed tomography images using Mimics software. The steady-state condition was performed for the simulation of 3D constructed models. On the other hands, the patient-specific geometry was modelled as unsteady flow. Blood was assumed as incompressible, homogenous, and Newtonian fluid. The outflow pressure was set at the outlets. Aorta wall was assumed as rigid and no-slip. The simulations were performed by using ANSYS Fluent software. The findings from the 3D constructed models indicated that max velocity which formed as a thin bar within the aneurysm is gradually increasing across the four-angulated neck abdominal aortas, this occurs because of the increase of the degree of angulated neck of AAA, while the results of patient-specific simulation showed that the blood flowing through severe bending of angular neck leads to high turbulence and asymmetry of flows within the aneurysm sac resulting in blood recirculation and high wall shear stress (WSS) near the AAA neck and on surface of aneurysm sac. However, the results for both cases have confirmed that there is a vital impact on the velocity flow field and WSS due to the angulated neck. In conclusion, this study explained and showed flow behaviours and WSS progression within high angulated neck of AAA in both studies of steady-state and transient conditions in the idealized and the realistic angulated neck of AAA models. Furthermore, it can be seen that the CFD technique has high performance in investigating and explaining the hemodynamic changes for angulated neck of abdominal aortic aneurysm which can be used as an extra tool to assist clinicians to understand the flow behaviour and manage for the clinical intervention.