Flow Studies in a Model of the Abdominal Aorta

Abstract

Biofluidmechanic effects play a role in the formation of atherosclerotic plaques, especially near branch points and bifurcations.

As an example, we chose a rigid polyester resin and an elastic silicone rubber model of the abdominal aorta. The model was prepared from a cast of a 27 year old woman who died of trauma.

The flow in the model was visualized using a birefringent solution (vanadiumpentoxide). Zones of flow separation, disturbed flow regions, coherent structures can be seen clearly. This method can be used for steady and pulsatile flow, in contrast to the dye method.

Laser-Doppler velocity measurements were carried out using a one component LDA system. 3D velocity measurements were done simultaneously in a simplified 90°-T-junction.

All the biofluid mechanic factors were studied separately in the models; factors such as steady and unsteady flow, elasticity of the wall, geometry, flow rate ratio, and non-Newtonian flow behavior of blood in secondary flow regions.

At high branch-to-trunk flow ratios (> 0.3), flow separation zones were observed in the aorta downstream of the renal arteries.

In pulsatile flow, flow separation zones were found at nearly all branch-to-trunk ratios. With increasing flow (higher Reynold-numbers) and in a range of normal pulse waves, flow separation almost disappears.

The elasticity of the wall reduces the flow separation effects, in comparison to a rigid wall.

Also non-Newtonian flow behavior can not be neglected. The flow always formes coherent structures at bifurcations. A totally different velocity distribution was found compared to a Newtonian fluid with the same viscosity.