Experimental investigation of unsteady inertial effects in physiological cardiovascular flows

The objective of this study was to examine inertial effects in a 180-degree curved artery model subjected to physiological flow conditions characterized by the dimensionless Womersley number. In cardiovascular flows, the Womersley number is typically defined by the frequency related to the duration of inflow conditions and the blood's kinematic viscosity. The multi-harmonic nature of pulsatile physiological waveforms suggests a range of Womersley numbers corresponding to the harmonics. Collectively, the multiple harmonics in the flow may distort measurements in cardiovascular flow experiments and affect correlations with human vascular flow conditions. Using water as a Newtonian blood analog, we explore these flow conditions in a loop with a 180-degree bend, programmable pump, and pressure and flow rate sensors. The experiment was designed with dynamic similarity principles and treated as a linear, time-invariant system, characterized by the total harmonic distortion. By combining pressure-time and flow rate-time measurements, the experiment was calibrated with analytical solutions from axisymmetric, unsteady Navier-Stokes equations. Within the flow loop we audit experimental conditions, signal inputs, and measure physical quantities such as flow rate and pressure gradients, as well as validate physiological parameters, including wall-shear stress, thereby enabling the study of complex cardiovascular flow conditions.