Critical rotating speed of rotor cup in an air suction open-end spinning machine

Simulation of three-dimensional turbulent flow in a rotor spinning machine is carried out, and the flow structure and behavior in the rotor cup are analyzed. The governing equations are the steady three-dimensional Navier–Stokes equations and the Spalart–Allmaras turbulence model. The results show that the rotating speed has great influence on the flow behavior in the rotor cup. It is found that there is a critical speed of the rotor cup beyond which the pressure and velocity on the slip surface is not changed anymore regardless of the magnitude of the rotating speed. When the rotating speed is larger than this critical speed, the flow structure becomes unstable with the increasing of the rotating speed. The mechanism of this phenomenon is that the airflow in the rotor groove passes about 180 degrees from two sides along the rotor wall and a pressure balance is achieved. When the rotating speed is larger than the critical speed, the balance will break down. When the rotor speed is low, the flow characteristic in the air-inlet plane is mainly determined by the high-speed airflow at the outlet of the transfer channel. However, when the rotor speed is higher than the critical speed of n = 80,000 r/min, the flow behavior is mainly determined by the rotating rotor. In the meridian plane perpendicular to the air-inlet plane, the flow behavior is mainly determined by the rotor speed. The rotating speed of the rotor has little effect on the flow characteristics in the transfer channel.