Study on the flow stability and dynamic characteristics of a water bearing

Abstract

The dynamic characteristics of the sliding bearing have great influences on the vibration and stability of the rotor-bearing coupled system. This study focus on a water lubricated bearing which supports the vertical rotor in atest facility. This rotor system is designed with maximum rotational speed of 5000 rpm and used to study the influence of water bearing on the rotor dynamics. Based on the unsteady computational fluid dynamics, a 3D model for the water film in the bearing with 3 grooves was built. The pressure oscillation in the water film was discussed. The dynamic characteristics including damping, stiffness and added mass of the bearing were calculated considering both the rotational effect and squeeze effect. The influences of the rotating speed of the shaft and prewhirl speed at water film inlet on the dynamic performance were also investigated. The results show that the instability of the film force on the journal is induced by the high-frequency vortexes in the grooves on the pad. At each rotational speed, the film force on the journal first decreases and then increase as the frequency ratio, while it increases with the increase of the rotational speed at each frequency. The rotational speed has great effects on the dynamic characteristics of bearing. Increasing the rotational speed contributes to strengthen the stability of the rotor system. The prewhirl velocity at the inlet has little impact on the dynamic characteristics and stability of the bearing. This study demonstrates the mechanism of lubrication dynamic characteristics of the siding bearing and shows the bearing nonlinear characteristics with the rotational speed. Using the CFD method to solve the water flow field is effective to predict the dynamic characteristics and can provide boundary conditions for the rotor dynamic analysis in the future study.