Dynamics and morphological evolution of a fiber conveyed in a three-dimensional rotor spinning unit: a numerical study

To interpret why rotor-spun yarns have fewer straight fibers, numerical simulations are performed to explore the fiber dynamics and morphological evolution during its conveyance in a rotor spinning unit by the airstream. Results show that the fiber experiences a sharp speed increase after reaching the shear boundary layer of the rotating wall. The sharp speed increase ends when the fiber arrives at the rotor groove where its morphology and speed barely change. The fiber straightness undergoes a process of first decreasing and then increasing during the conveyance and the worst fiber straightness is obtained halfway during the fiber's sliding process. Compared with the fiber transport channel (FTC) angle, the rotor speed and the suction pressure play a more important role in affecting the fiber dynamics and morphological evolution. Fiber can be more efficiently conveyed as the rotor speed increases or/and the suction pressure decreases, and its straightness varies non-monotonically with these two parameters. Too low or too high rotor speed and suction pressure could result in a decrease in the fiber straightness, and the straightest fiber is obtained at a medium rotor speed of 80,000 rpm and a medium suction pressure of −8000 Pa for our considered system parameters.