Numerical Simulation And Optimization Of Weft Insertion Flow Field Of Air-jet Loom

Weft insertion in air-jet loom is operated by high speed air jets emitted by a main nozzle.The main nozzle works as an ejector which can suck yarn and drive it through the warp shed by the friction between air and yarn.Air-jet loom has a higher performance of a picking system and wider applications compared with conventional looms.The micro-electrical control technology and optic-mechanical-electric technology of air-jet loom is the highest among four kinds of shuttleless looms.Due to the lack of systematic theoretical analysis and complete experimental methods,air-jet looms rely on imports for a long time,which has been one of the difficulties in the industry.In this paper,the characteristics of the weft airflow are analyzed.The air-jet flow is defined as compressible viscous steady turbulent flow.The mechanical model and physical model is established according to its flow characteristics.The governing equations of the air-jet flow are established by using the basic laws of physics,which provide the theoretical basis for numerical simulation of the weft insertion.Computational study using commercial code FLUENT was performed to explain the flow field in the air jet nozzle.A test stand for airflow of air-jet loom is set up,and the airflow velocity in the reed groove is measured in order to verify the numerical simulation results.The numerical simulations of two kinds of main nozzles with different throat structures show that: The airflow velocity at the exit of acceleration tube of main nozzle B which has a subsonic-supersonic throat structure is 10m/s higher than main nozzle A which has a subsonic throat structure.The main nozzle B has a weaker back-flow phenomenon,a higher air drag force and a little more air consumption than main nozzle A under the same supply pressure.The numerical simulations of single-hole relay nozzle and three different kinds of relay nozzles with different tapers show that: Cone-hole relay nozzle air-jet flow velocity decay rate is slightly slower than the single-hole relay nozzle under the same supply pressure.At the same range,the velocity of the air flow in descending order is as follows: cone angle of 30°> cone angle of 60°> cone angle of 45°>cone angle of 0°.Cone-hole relay nozzle has a better airflow direction and bundling and lower gas consumption than single-hole relay nozzle.At the same supply pressure,the air consumption in descending order is as follows: cone angle of 0°> cone angle of 30°> cone angle of 45°> cone angle of 60°.The numerical simulations of synthesis flow field composed of main nozzle,relay nozzles and profiled reed show that: It is necessary to use RNG k-? turbulence model and Scalable wall functions to analyze the air-flow field.Weft insertion flow filed can be divided into two parts: one is a synthesis flow filed of main nozzle,single relay nozzle and profiled reed;the other is a synthesis flow filed of a number of relay nozzles and profiled reed which can be regarded as the superposition of flow field composed of single relay nozzle and profiled reed.The jet-flow of main nozzle only has a slight influence on the velocity of the first relay nozzle,resulting in a velocity increase.Simulation results of airflow velocity at different measuring positions in the groove indicate that the airflow in the reed groove flushes toward the inner wall and the upper wall of the reed groove.