Reducing fiber wastes in vortex spinning via flow modulation induced by grooved spindle inlets

Serving as the core of vortex spinning, precisely controlling fiber motion in the tangentially injected swirling flow inside the nozzle remains a challenge. Fiber wastes during the yarn manufacturing process compromise yarn quality, necessitating persistent optimization of the nozzle structure. By incorporating grooved spindle, stable primary recirculation vortex (PRV) is generated to enhance fiber adherence through its entrainment effect, thereby reducing wastes. Large eddy simulation with parametric modeling is employed to investigate the flow behavior for the grooved spindle inlets. Transient vortex evolution and turbulent characteristics are analyzed to evaluate the flow modulation performance of the grooves. A single-grooved design with expansion ratio of 1 generates a weak, unstable PRV with low turbulent kinetic energy and dissipation rate. An expansion ratio of 2 stabilizes the PRV but induces intense fluctuations of the vortex near the arc-shaped spindle tip wall and wall shear stress, intermittently disturbing fiber wrapping. The multi-grooved design results in a 61.8% increase in the circulation of the vortex near the arc-shaped wall, an increase in the Ω value of 15.3%, and a more uniform wall shear stress, facilitating uniform fiber wrapping. Experiments show that, compared with the ungrooved design, fly is reduced by 74.7%, fibers expelled from nozzle by 22.9%, yield increases by 3.2%, and yarn breaking tenacity improves by 10.5%. Good agreement between simulation and experiment results confirms the efficacy of the design. The grooves only modify the spindle inlet configuration and maintain the spindle fit with the nozzle, thus facilitating rapid industrial application.