Flow behavior and blockage effects in stenosed arteries

Abstract

Flows, both steady and pulsatile, through a circular tube with an axisymmetricblockage of varying size are studied experimentally and numerically. Selectedas an idealized model of a stenosed artery at various points in its development,the geometry consists of a long straight tube and a blockage, semi-circular incross-section. The stenosis has been simplified to a single-parameter blockagein order to highlight fundamental behaviors of constricted flows. Experimentally,a water flow is considered inside a tube of 19mm diameter, which has anunblocked length of 2 m both upstream and downstream of the blockage. Theflow is characterized using dye visualisations and Particle Image Velocimetry. These results are complemented by spectral-element numerical simulations.The study initially looks at steady inlet flows, using them as a limiting case forpulsatile flow. At low Reynolds numbers, the flow is characterized by a jet emanatingfrom the constriction, surrounded by an axisymmetric recirculation zone,the length of which increases linearly with Reynolds number. Our numericalresults indicate a critical Reynolds number threshold for absolute instability,while our experiments point to the existence of convective instabilities at lowerReynolds numbers.Flows subject to a pulsatile inlet condition, which more closely describe thetype of flow found in the cardio-vascular system are also investigated. With aparticular focus on the effects of the blockage size, we investigate the stabilityof such flows, transition to turbulent flow and also other physical properties pertinent to cardiovascular fluid mechanics, such as wall shear stress.