Lobed Swirl-Inducing Ducts for Blood and Blood-Like Fluids

This research report details the development and analysis of a lobed swirl-inducing duct designed to facilitate the transport of blood and blood-like fluids, addressing the critical issue of red cell aggregation and subsequent clotting caused by deficiencies in modern tubing systems. The core aim of this work was to incorporate existing industrial swirl technology into duct geometry to efficiently induce and maintain the natural swirling motion of blood flow without creating adverse flow behaviour or circulatory problems. The methodology involved extensive computational fluid dynamics (CFD) modelling using ANSYS Fluent, focusing on the geometric degrees of freedom, mathematical/fluid-dynamic relations, and optimised duct designs. An initial lobe series was investigated, followed by the refinement and optimization of elliptical cross-sections, specifically the 8R 2a/b Ellipse and the 8R 2.2 a/b Ellipse. Key performance indicators throughout the investigation included Swirl Number (S), Swirl Effectiveness, total pressure loss, and axial/circumferential velocity profiles across Reynolds numbers ranging from 50 to 700. The optimization phase demonstrated that elliptical designs, particularly the 8R 2.2 a/b Ellipse, significantly improved swirl generation capability. This model was found to generate the highest recorded swirl number (up to 2.25 at a Reynolds number of 700 in the x-direction) and achieved superior swirl effectiveness by generating greater swirl magnitude for the corresponding pressure loss incurred. Subsequent experimental validation using a 3D printed 8R 2.2 a/b Ellipse prototype and water as a fluid medium confirmed the flowrates and pressure loss characteristics derived from the Newtonian fluid simulations. For cardiovascular transferability, transient simulations employing a Casson viscosity model to mimic non-Newtonian blood rheology and an optimised spatial frequency progression were performed. These simulations confirmed that the final design could produce localized shear rates of up to 170(s⁻¹) near the walls and sufficient shear in the core region of up to 115(s⁻¹) at 700Re, which was adequate to dis-aggregate red cell rouleaux formations and deter clotting mechanics. These findings demonstrate that the optimised swirl-inducing duct can impose a helical flow regime that offers vital rheological benefits, ensuring more efficient circulation and mitigation of clotting, making these results valuable for developing industry standard swirl ducts and potentially integrate this swirl feature in medical grade tubing. This may lead to developing swirl-stent scaffolding variations of the designs discussed in this work.