ARTERIAL STENOSIS
Using both computational and experimental methods, we are considering the hemodynamics of stenosed arteries. After conducting extensive work on an idealized, axisymmetric geometry, we are now investigating eccentric stenoses and patient-specific geometries. Patient-specific geometries are requiring a new method for manufacturing the test sections and one of our projects is focussed on this process, using PDMS and 3D printing for the moulds.
Arterial stenosis is a condition where a narrowing of the artery causes a disruption in the blood flow which can result in turbulent flows in the severe cases. This condition is usually caused by a build up of cholesterol plaque in the arterial wall, known as atherosclerosis. As such, the analysis of fluid dynamic quantities such as velocity profiles, turbulent quantities and wall shear stress (WSS) are important in gaining an understanding of the mechanisms that contribute to the initiation and progression of these conditions. Since the in vivo measurements are difficult, computational simulation provides an alternative methodology to investigate these effects. The following shows the temporal CFD (LES) results of the axial velocity (left) and vorticity (right) with the physiological temporal velocity profile (bottom). Barber et al. (2010) "Large eddy simulation of a stenosed artery"
By plotting a contour of WSS around the vessel (circumferentially) in the y-axis, and along the vessel length in the x-axis, vessel wall can be opened out and the WSS over the entire vessel wall can be visualized as in the following. The WSS contour is plotted at 6 time points over the cycle. Highest levels of WSS (150 Pa) are found at the stenosis during the peak systole stage of the cycle (t=0.1s) since the greatest amount of fluid flow through the small regions of the stenosis. Another region of high WSS is also found downstream of stenosis (around 5D) where the shear layer break apart and create disturbed flow outside of the central core.
Experimentally, laser sheet visualization is used with a continuous Nd-YAG laser to highlight regions of the flow field, including the post-stenotic jet core field as well as the associated recirculation regions, as shown in the following. To obtain reasonable experimental data, two non-dimensional parameters, Reynolds number and Womersley number are used to scale up the geometry of a femoral artery from the typical diameter of 10 mm to 31.7 mm. To retain dynamic similarity with the given fluid properties, pulsatile inlet profile period is also increased from a real life situation of 0.6s to 28.14s. Barber et al. (2012) "Post-stenotic flow in an artery"
The following shows the video results of the LES CFD simulation (left) and the laser sheet flow visualization (right) and the comparison of the CFD and the experimental mid-plane flow field results for validation (bottom).
