FLOW CHARACTERISTICS OF THE MAIN NOZZLE IN AN AIR-JET LOOM .2. MEASURING HIGH-SPEED JET FLOWS FROM THE MAIN NOZZLE AND WEFT DRAG FORCES

In this research, the jet-flow characteristics under tank pressures of 2 approximately 6 kgf/cm2 were studied to obtain basic data for an optimal design of the main nozzle in an air-jet loom. Furthermore, wefts were actually inserted in the nozzle and weft traction forces were measured. Axial changes of the nozzle jet speed and jet diameter below the tank pressure at which choking arises at the exit of the acceleration tube are largely different from those above that tank pressure. Choking arises within the upstream region in the acceleration tube (Mach 1), and the Mach number at the tube exit exceeds 1. When this happens, expansion waves occur owing to underexpansion, and the oscillation of compression and expansion waves can be seen in the downstream region. Therefore, the weft drag force F, which represents the weft-flying property in a nozzle, increases in proportion to tank pressure P(T). But when the flow is choking at the exit of the acceleration tube, the drag force F becomes nearly constant, even at higher tank pressures.