Numerical analysis of jet orifice geometrical effect on airflow characteristics in FDY yarn suction gun

Software CFX 12. 1 is used to simulate airflow patterns in the yarn suction gun with different geometrical parameters of the jet orifice,the relation between the airflow patterns and yarn suction performance was discussed,and the affecting mechanism of jet orifice geometry on the yarn suction performance was clarified,and the rational parameters were obtained as follows: the number of jet orifices N = 3,the diameter of jet orifice d = 2. 0 mm and the angel of jet orifice = 75°. The results show that an increase in the number of jet orifices reduces free diffusion of the jet stream,enhances its directivity,and increases air density and circumferential velocity component near the gun wall,thereby increasing the yarn suction force; and overlarge number of jet orifices increases the conflict between the jet streams,and decreases the yarn suction force. An appropriate diameter of jet orifice is conductive to the formation of a strong swirling flow,and avoids the occurrence of a normal shock wave,thereby improving the yarn suction force. The angel of jet orifice mainly controls the magnitude of the air circumferential velocity component,and causes the variation of the swirling flow intensity,thereby varying the yarn suction force.The yarn suction efficiency has a close relationship with the airflow distribution,and especially the air circumferential velocity component has the biggest influence. The generation of the normal shock wave was not conductive to the increase of the yarn suction force,which should be avoided as much as possible.