Characterization and Scaling of Pulsatile Helical Flow: An Experimental Investigation

Pulsatile helical flow is a prominent physiological characteristic in circulatory systems, including the heart, aorta, vessel bifurcations, umbilical cord, and respiratory systems. Helical patterns indicate healthy blood flow, offering benefits such as improved perfusion, reduced oscillating wall shear stress, and decreased energy loss. However, systematic characterization of these patterns is limited due to the lack of benchmark models. This study developed an experimental setup to observe laminar helical flow and its transition to turbulence across a range of Womersley numbers (Wo), Reynolds numbers (Re), and Pulsatility Indices (PI). Helical pipe models with physiological curvatures and torsions were incorporated into a closed flow loop with steady flow pumps and a programmable pulsating pump to maintain constant and oscillating velocity components. High-frequency pressure transducers and ultrasonic flow sensors recorded pressure and flow rates. Particle Image Velocimetry and Laser Doppler Velocimetry explored vortex flow characteristics along the helical tube, measuring helicity as a function of Wo, Re, and PI. Results suggest a reliable scaling law for global helicity, potentially allowing for quick, accurate estimation in clinical settings. Helical flow alters turbulence onset thresholds in pulsatile pipe flows. Understanding pulsatile helical flows provides insights and potentially leads to advancements in diagnosing and treating cardiovascular and respiratory diseases.