Numerical Simulation of Airflow Characteristics in Air Suction Gun

We investigated numerically flow patterns in the air suction gun and dependence of the flow pattern on the supplied air pressure in order to clarify the working mechanism of an air suction gun. The compressed air issued from compressed-air inflow tubes into a yarn passage accelerates with sucked ambient air owing to negative pressure generated by the compressed air, and attains a critical speed near the throat of the de Laval tube and a supersonic speed in the divergent part of the de Laval tube. The supersonic flow generates a normal shock wave and changes into a subsonic flow. Then, the air is discharged into the atmosphere. Since this compressed air has a circumferential component, it forms a helical flow along the wall of the yarn propulsion tube composed of the de Laval tube and the straight tube. Velocity and density of the helical airflow near the wall are larger than those near the centerline. The suction efficiency is promoted greatly owing to this high focusing ability (bias of high speed and density flow toward the vicinity of the wall) and a large yarn length in the helical airflow. Increased supplied air pressure brings about increases in both air density and supersonic flow region, which promotes the yarn suction force.