Coupling Of Jet-led Flow Field-weft Yarn Based On Large Eddy Simulation

In industrial production,air-jet loom has the characteristics of high productivity,fast weft-launching speed,and strong adaptability to varieties,etc.The weft-launching system is composed of main nozzle,auxiliary nozzle,and profiled reed,and its weft-launching quality and efficiency mainly depend on the flow characteristics of the synthetic flow field.Therefore,this paper takes the air jet loom weft guidance system as the research object,and uses theoretical analysis combined with numerical simulation analysis to study the flow characteristics of the free jet of the auxiliary nozzle and the synthetic flow field characteristics when the main jet and auxiliary jet flow converge into the shaped reed,and finally discusses the flow-solid coupling characteristics of the airflow with the yarn in the synthetic flow field:(1)The steady-state model of the auxiliary nozzle free jet is established,and the steady-state flow field characteristics of the free jet of three auxiliary nozzles,conical,cosine and cylindrical,are studied,and the velocity variation trend along the central axis under transient conditions and the velocity fluctuation range are derived using the large eddy simulation method,and finally the radial velocity distribution of the three auxiliary nozzles is compared,and the velocity fluctuation at the end of the core region of the jet under transient conditions is monitored Velocity fluctuations to determine the dissipation of the auxiliary jet,the results show that: cylindrical auxiliary spray generated by the airflow diffusion effect should be the smallest,but its airflow velocity is the lowest,affecting the efficiency of the work,cosine auxiliary spray velocity decay is the slowest,but its airflow diffusion effect is the largest,affecting the lead weft stability,cone-shaped auxiliary nozzle jet characteristics are more moderate.Using the sub lattice stress model in the large eddy simulation to simulate and calculate the main nozzle and auxiliary nozzle converge into the synthetic flow field in the shaped reed channel,while comparing the RANS method with the LES method based on the change in the axial velocity of the main spray center of the synthetic flow field,and studying the axial velocity change in the center of the synthetic flow field,the radial velocity change and the fluctuation of the velocity of the main nozzle and auxiliary nozzle when the flow converges with time.The characteristics of the vortex structure diagram of the conical auxiliary nozzle are described to be able to study more specifically the motion of fluid turbulence at high Reynolds number.The results show that the cone-shaped auxiliary nozzle has a better effect of inducing weft;comparing the two types of methods used to identify the vortex structure,it can be shown that the Ω method has the characteristics of deterministic threshold range and high accuracy of vortex identification.(3)The kinematic model of yarn fiber structure is established,and a two-way coupling method of fluid dynamics and structural dynamics is used to study the motion state of yarn in the synthetic flow field and the effect of yarn motion within the coupled flow field on the synthetic flow field,and the results show that the minimum deformation of yarn in the coupled flow field of cone-type auxiliary nozzle is about 1.2 mm,the minimum radial displacement above and below the center point of yarn is about The main stress of the yarn in motion fluctuates periodically and smoothly with a maximum of 1.59 PMa;using the LES method,the convergence of the airflow between the main nozzle and the auxiliary nozzle in the shaped reed channel is stronger and the deformation of the yarn is smaller compared with the RANS method.The conical auxiliary nozzle has the best convergence of airflow in the coupled flow field.By analyzing the flow characteristics of different structures of auxiliary nozzles and the convergence of main and auxiliary nozzles into the synthetic flow field in the shaped reed,the coupling effect of yarn and synthetic flow field is finally studied to understand the influence law of auxiliary nozzle structure on the flow characteristics of transient flow field,which provides reference for the optimization of auxiliary nozzle structure of subsequent weft guiding system.