Abstract:

Objective The auxiliary nozzles are key components in air jet looms. While the single circular auxiliary nozzles have problems of low speed, poor air concentration and high air consumption, this research aims to design a new type of auxiliary nozzle with special-shaped hole and to study the influence of the structural parameters of auxiliary nozzles on the synthetic airflow in the profiled reed. A three-dimensional(3-D) synthetic airflow field consisting of a main jet and auxiliary nozzle jets was numerically simulated based on the Reynolds time-averaged equations (RANS) and eddy viscosity turbulent model.
Method 3-D model of synthetic airflow field of different Y1, Y2 and Y3 type of auxiliary nozzles were established with Solidworks before the 3-D synthetic airflow model was meshed with professional ICEM software and the boundary conditions were set in the CFD software Fluent. The numerical simulation on the synthetic airflow model was accomplished based on the RANS equations. The numerical simulation results were validated by the experimental results. Thereafter, the comprehensive comparison of synthetic airflow characteristics and air consumption were investigated for single round-hole and Y1, Y2 and Y3 type auxiliary nozzle with different structure parameters under same gas pressure.
Results The simulation results were in agreements with the experimental test results regarding the synthetic airflow velocity trend. When the airflow from an auxiliary nozzle jet was injected into the profiled reed and merged with the main jet, the synthetic airflow experienced attenuation. The Y2 type relay nozzle has the minimal attenuation, and the airflow speed was 8 m/s higher than that of the auxiliary nozzle with a single circular hole structure. The inject angle of auxiliary nozzle was found to have a significant impact on the velocity of the synthetic airflow. The inject angle of the Y2 type auxiliary nozzle varied between 4°and 7°, while the speed deviation of the Y2 relay nozzle was 13 m/s. The outlet shape of auxiliary nozzle was also found to have influence on the turbulence distribution of the synthetic airflow in the profiled reed. The outlet shape of auxiliary nozzle demonstrated effects on the velocity and direction of the synthetic airflow. The jet core speed of the Y2 auxiliary nozzle jet was 320 m/s and the jet core velocity area is the longest, better than single circular hole auxiliary nozzle. On the other hand, the single round-hole jet core area is the smallest and spreads quickly. The weft thread was pulled forward by the high-velocity airflow in the profile reed. The outlet shape had an influence on the weft insertion stability. The radial velocity of synthetic airflow was measured at three cross sections of 5 mm, 10 mm and 15 mm from the first auxiliary nozzle outlet, respectively. The radial velocity amplitude and the equivalent circle radius are largest for the Y2 type auxiliary nozzle. Statistics on the mass flow rate at the outlet related to the gas consumption of three types of auxiliary nozzles.
Conclusion Based on the above simulation analysis, some useful results are obtained. Compared the single round hole auxiliary nozzle with the Y2 type auxiliary nozzle, the average velocity increased by 6% and the maximum velocity increased by 12%. The injection angle of auxiliary nozzle is a sensitive factor that affects the axial velocity of synthetic airflow in the profiled reed. A small change in the injection angle will have a significant impact on the velocity of synthetic air flow in the profiled reed. Among them, the best injection angle of Y2 auxiliary injection is 4°. The maximum speed of the potential core of the Y2 type auxiliary jet flow reaches 324 m/s, and the potential core area is the longest. The Y2 auxiliary jet can converge with the main jet at a higher speed. At the section 10 mm away from the auxiliary jet outlet, the radial velocity of Y2 type auxiliary jet flow exceeds 80 m/s, and the equivalent circle radius is significantly greater than that of single circular-hole auxiliary nozzle. It can be seen that the radial velocity attenuation is the slowest and the stability of weft insertion is the best with the Y2 type auxiliary nozzle.

Key words: weft insertion synthetic airflow, profiled reed, special-shaped hole auxiliary nozzle, weft insertion stability, gas consumption, air jet loom