Dynamic Behaviors Analysis Of Oil Film-Pivot Tilting-Pad Bearing-Rotor System

With the increase in speeds of rotating machinery, its performance requirements need to be improved unceasingly. The problems of the tilting-pad journal bearing, such as the complex mechanical structure, the wearing of the pad pivot and the insufficient damping, have become the main aspects of the impact on the improvement of the performance. The new tilting-pad journal bearing studied in this paper transforms the mechanical pivot of traditional tilting-pad journal bearing to oil film pivot. The new bearing have two layers of lubricating oil film, which can greatly reduce the mechanical pivot wear, and increase the damping of the system. In this paper, the dynamic characteristics of the oil film tilting-pad journal bearing and the rotor-bearing system have been primarily studied.Firstly, considering the characteristics of pad swing, the Reynolds equation of oil film pivot tilting-pad journal bearing has been set up based on the hydrodynamic lubrication theory of journal bearing. By using the finite difference method, a Matlab program has been designed to solve the Reynolds equation, which is under the condition of known bearing operating parameters rather than the eccentricity. Then the tilt angle of bearing pad, the deviation angle and the eccentricity of the bearing are got.Secondly, based on the eight dynamic coefficients of linear oil film force model, the stiffness and damping coefficients of the oil film pivot tilting-pad journal bearing have been solved. And the influence of working speed and load on dynamic characteristics coefficients of the inner oil film has been analyzed. The bearing-rotor system has been simplified as two models, which are two-mass-spring-damper system and equivalent mass spring-damper system. Then by using differential equation of motion, the comprehensive stiffness and damping of oil film have been deduced, and the support state of oil film pivot tilting-pad journal bearing has been studied.Thirdly, the critical speed and unbalance response of the rotor system have been calculated and analyzed by using Samcef/Rotor which is a special rotor dynamics finite element analysis software. The results show that in the larger range, with the increase of the stiffness, the critical speed increases, and the damping has little effect on critical speed. When the support stiffness increases, the amplitude of the displacement response increases; and when the support damping increases, the amplitude of displacement response decreases. Under the certain conditions, the oil film pivot tilting-pad journal bearing can increase the damping of the system, and reduce the stiffness, making the amplitude of displacement response reduce, which reflects a good vibration characteristics.Lastly, a large scale bearing test-bed has been use for experimental study. By the oil film-pivot tilting-pad journal bearing experiments, the change rule of rotor vibration displacement amplitude, frequency spectrum and seat vibration acceleration under different rotational speed have been analyzed. Through the contrastive analysis between large clearance ratio bearing and cylinder bearing experiments, it can be seen that the increase in clearance ratio can reduce the seat vibration acceleration, with the suitable structure parameters, the oil film pivot tilting-pad journal bearing is able to obtain a good vibration damping characteristics, which have laid a solid foundation and indicate the direction of the further research.