Air-flow characteristics and yarn whipping during start-up stage of air-jet weft insertion

Abstract

Air-jet weaving is a weaving technique with high production rate. However, efficiency decreases if instabilities in the motion of the weft yarn leader occur causing weft insertion failure. A 2D geometrical model was developed for the main nozzle of the air-jet loom and a mathematical model employing the fluid–structure interaction (FSI) technique was used to simulate the air-flow and whipping action of the leader in the air flow at the exit of the main nozzle. With numerical results, the resultant force normal to the yarn determined by the yarn shape and the air-flow field has a significant influence on this whipping action. Starting with an initial gravity-induced drooping leader, a large normal force exerted by the air flow subsequently leads to a strong whipping action. To verify the validity of the numerical analysis, an experimental apparatus with a high-speed camera attached was constructed to observe the leader trajectory under different air supply conditions. The experimental results show that during weft insertion the motion is more stable with an initially straight leader than one initially drooping.