Numerical Calculation And Experimental Study On The Characteristics Of The Yarn-airflow Two Phase Coupling In The Main Nozzle Jet

Weft insertion is the core part of air-jet loom, which transforms the high pressure gas to thesupersonic airflow. The supersonic airflow accelerates the weft yarn and finishes the weftinsertion. There is a close relationship among the flow characteristics, the interaction betweenthe airflow and the yarn and the yarn movement characteristics in the main nozzle, which play animportant role for the weft insertion efficiency and fabric quality.In this paper, we did the research based on the main nozzle and the guide tube, using thenumerical simulation research and the experimental analysis method to study the airflowcharacteristic in the main nozzle and the guide tube, the yarn movement characteristics andexperimental study. Firstly, we analyzed the airflow characteristic of influence. Then wesimulated movement of the yarn in different constraints under different internal pressure. Finallywe used experimental method to study the yarn characteristic by the same constraints, andcompare with the results of the numerical simulation. The conclusions specific as follows:1. The maximum velocity was concentrated near the throat of the main nozzle, and thevelocity could reach to the supersonic speed. The recirculation region appeared in the high to lowspeed airflow mixed area, and the airflow velocity was minimal in the region. With the increaseof the inlet pressure, the turbulent kinetic energy would increase, and the most violent atz=45mm. With the increase of the inlet pressure, the wall velocity near the boundary layer wouldincrease, which would lead to the air flow congestion in the thread tube.2. Numerical simulation of the yarn coupled with airflow by finite element method waseffective. The yarn would bend deformation under the airflow, and the radial displacementpresented trigonometric function form.3. Under the condition of fixed at one end, the principal stress would become larger whenthe yarn contacted with the nozzle wall and became bending. With the increase of the inletpressure, the principal stress would increase, however the wave amplitude would decrease.4. Under the condition of fixed at both ends, the principal stress would decrease with theincrease of the inlet pressure, and the fluctuation reduces. The most severe fluctuation part wasfocused on the tail and head end of the yarn.In summary, in the paper, we used the theoretical and experimental methods to research yarnmovement characteristic coupling with the airflow, which could provide a theoretical method forweft insertion.