Investigation of unsteady flow effects in cylindrical artery phantoms with physiological implications

The objective is to understand the physiological, pulsatile flow structures in cardiovascular flow experiments through the analysis of flow development and Stokes layer length scales. The degree of pulsatility in blood flow is commonly described by the Womersley number, which is defined as the ratio of transient inertia forces to viscous forces. It depends on the kinematic viscosity and the period of the flow waveform. The Womersley number facilitates our understanding of cardiovascular flows by linking the effects of unsteadiness with momentum transport. This study aims to clarify the effect of the Womersley number on unsteady velocity profiles, wall shear stresses, and the phase lag between pressure gradients and flow rate, studied in straight, cylindrical, rigid blood vessel phantoms. Experiments are carried out using water as a Newtonian, blood-analog fluid under various inflow conditions, including pure sinusoidal and multi-harmonic physiological flows across different Womersley numbers. Real-time flow conditions are tracked with blood pressure transducers and ultrasonic flow rate sensors. CFD simulations are performed using ANSYS Fluent to replicate the experimental flow conditions for validation and to gain a deeper understanding by complementing the experiment's limitations. Both experimental data and flow simulations offer insights into the role of Womersley number, which depends on blood viscosity that varies significantly throughout the circulatory system.