Abstract:

Objective In air jet looms, the weft yarn is propelled through a profiled reed channel by means of a synthetic airflow from a main nozzle and multiple relay nozzles. The structure of the relay nozzle directly affects the airflow speed, weft direction, and breakage rate during the insertion process. Although many researchers studied the fluid characteristics of single-hole relay nozzles, most of the published works ignored the interaction between airflow and the weft yarn. This paper aims to study the influences of structure parameters of multi-hole relay nozzles on the dynamic behavior of a clamp-free fiber bundle transformed by unsteady airflow in the profiled reed.

Method Three types of multi-hole array auxiliary nozzles were designed. The Arbitrary Lagrangian-Euler method (ALE) was employed to simulate fluid-solid interaction between the unsteady airflow and an elastic fiber bundle. The three-dimensional transient airflow has been simulated using ANSYS Fluent 2020, in which the fiber bundle is solved simultaneously using coupled scheme. Then, the motion displacements of fiber bundle were captured by a high-speed camera to confirm the accuracy of the numerical simulation. The image capture rate was adjusted to 10 000 frames's to capture the motion of the yarn. The influences of outlet shape, array layout, and inlet pressure of the auxiliary nozzles on the airflow velocity pulsing and the bending deformation of the fiber bundle were revealed.

Results The simulation results for the airflow velocity and bending deformation of fiber bundle were presented. In order to validate the numerical scheme, the motion deformation of the fiber bundle captured by the high-speed camera was compared with numerical simulation. As observed, a good agreement existed between the numerical and experimental values. Synthetic flow field-weft yarn coupling contour showed the velocity contour of synthetic airflow and motion deformation of the fiber bundle in different time steps for three types of relay nozzles. The influences of the outlet shape and array on airflow velocity and vortex formation were depicted. The influence of the relay nozzle on the fiber deformation was illustrated, the elastic fiber bundle was completely bent along the axial direction due to the friction force of the airflow. Moreover, the displacement value of fiber was the minimum with the three-round hole central array relay nozzle.

Conclusion The two-way fluid-solid coupling simulations have been presented. The simulation results of the fiber motion have been verified with experiments. Firstly, the deformation of fiber is minimum in the synthetic airflow generated by the three-round-hole central array relay nozzle. Secondly, the velocity gradient of synthetic airflow is minimal in this relay nozzle. Thirdly, with the increasing bending deformation of the fiber bundle, the velocity gradient of synthetic airflow along the axis of the fiber increases significantly. The proposed multi-hole relay nozzles could be applied to any type of air jet looms. Especially, the circle-round central array relay nozzles could reduce the weft breaking rate at high speed.

Key words: air-jet loom, weft insertion efficiency, fluid-solid coupling, relay nozzle, synthetic airflow