Experimental and CFD-DPM analysis of Dean-number-dependent secondary flows and particle transport in bifurcating Y-junction ducts

Curvature-induced secondary flows in bifurcating conduits govern cross-stream transport, vorticity amplification, and particle residence, with direct relevance to vascular-like and engineered flow systems. This study presents a combined experimental–numerical framework to quantify Dean-number-dependent secondary flows and particle transport in carotid-like Y-junction geometries. Dye-front visualisation in a straight pipe was employed to validate a Computational Fluid Dynamics-Discrete Phase Model (CFD-DPM) framework and identify an appropriate representative particle scale. Among particle diameters of 1, 7, and 15 µm, the 7 µm particles showed the closest experimental–numerical agreement, with a discrepancy of approximately 1.7%, and were therefore selected as a blood-cell-scale tracer reference. Secondary flow characteristics were quantified using swirling-strength and vorticity-based metrics as functions of branch angle and Dean number. Secondary vortices were absent below Dean numbers of approximately 180 and became fully developed between 200 and 250. Increasing the branch angle from 15° to 60° reduced the effective curvature radius from 107 mm to 28 mm and increased the Dean number to nearly 350, resulting in vorticity amplification from 6.8 s⁻¹ to 20.4 s⁻¹. In the 60° junction, pulsatile inflow produced the strongest enhancement of swirling strength. Particle transport exhibited strong scale dependence, with nanoscale particles showing approximately 45% retention under non-Newtonian flow conditions, whereas blood-cell-scale particles remained predominantly advection-driven, with nearly 80% exiting the junction. These findings establish quantitative relationships between bifurcation geometry, Dean-number-controlled secondary flows, and particle transport dynamics, providing an experimentally validated framework for analysing transport phenomena in vascular and engineered bifurcating systems.