Influence of inflow conditions on simulations of arterial blood flow

Sammanfattning: The blood is responsible for the oxygenation of the body and to carry nutrients to the different parts of the body and waste products away from the major organs like the liver, kidneys but also the walls of the arteries. Blood is composed of red blood cells that are on average 45% of the total volume, the rest of the blood is made up of blood plasma platelets, white blood cells, minerals and nutrients. The red blood cells are responsible for the distribution of oxygen and CO2. To facilitate the distribution of oxygenated blood the circulatory system is used to make sure that blood is reaching the parts of the body. The largest artery in the body is the aorta, which connects the heart to the rest of the body. The aorta is composed of the ascending aorta, the aortic arch and the descending aorta, the ascending aorta have the heart valves connected to it. The descending aorta has two parts the thoracic and the abdominal aorta. The abdominal aorta is in the lower part of the body and bifurcates into smaller arteries that connects to the kidneys and liver. The aortic arch is a bifurcation part that splits the blood flow up into, the Brachiocephalic artery the Left common coronary artery, the Left subclavian artery and the descending aorta. The walls of the aorta is made up of layers so that the aorta can be anchored to the surrounding organs to maintain stability. Leaving the heart, the blood flow features are clearly influenced by the hearth valves as well as the shape of the root. It is the movement of the valves and the following change in pressure and velocity that is one of the underlying mechanism for the observed flow features. As the discharged blood is traveling up the ascending aorta the curved nature of the aorta will affect the flow. The time-varying flow field will result in a shear stress at the wall which under certain circumstances can results in a hardening or build up of the artery wall [5]. The shear on the wall in the descending aorta depends on the inflow condition and the geometry effects on the flow field, both for the aorta and the inflow area.   The reason for CFD simulations of the human aorta is due to the high prevalence of cardio-vascular decease in the western world with the purpose to further understand the underlying mechanisms responsible thereof. The challenge in such simulations lies in complexity of the circulatory system, making a well-resolved fluid simulation of the entire system not feasible. This is due to the demand of computational power needed to obtain well resolved geometries as well as flow features properly describing the fluid flow. Reducing the model of interest for simulations, leads to another challenge, which is posing the proper boundary conditions.   In computational fluid dynamics the boundary conditions are what in part defines the solution, the conditions on the boundaries are a source of debate between accuracy, realism and computational efficiency and here are where the compromises are found and also what is to be simulated. These choices becomes more apparent as the complexities of the physical domain is taken into consideration. In this case there is bifurcations along the domain with outflow conditions that will effect the flow field. So the inflow conditions effect on the solutions are an important aspect when considering the flow field downstream of the boundary.   The goal of this report is twofold, firstly it is to simulate the flow field in the aorta for four different cases. With the end goal of in detail investigate the flow field in the descending aorta. Secondly it is to using a simpler geometry and a more complex inflow condition to simulate a more complex geometry. Focus will be placed on the flow field in descending aorta, and how the inflow conditions are effecting flow. The core of the question is how the boundary conditions are effecting the wall shear and the how the disturbances are advected down into the descending aorta.