Rotordynamic characterization of tilting-pad bearings with eight pads in vertical rotors

It has been documented that stiffness and damping for a four-pad bearing are dependent not only the magnitude of the load but also on the position of the rotor in the bearing. However, 8-pad bearings are not commonly employed on horizontal turbines, and the presence of several pads in the bearing will decisively affect the dynamics of the system. This paper evaluates the stiffness and damping coefficients of tilting-pad bearings with eight pads and explore the main frequencies acting on the forced response of a vertical rotor. The bearing properties were modeled as a function of eccentricity and position in the stationary coordinate system by Navier-Stokes equations whose results are taken from commercial software. The simulated unbalanced response is compared to experimental results; the changing position of the shaft produces a periodic stiffness and damping, which is dependent on the number of pads. Cross-coupled coefficients influence is discussed, showing that their absence makes an accurate model for the mean values. The results indicate that simulation of vertical rotors with 8-pad bearings can be simplified which allow more effective simulations and dynamic analysis.

A comparative experimental study on large size center and bi-directional offset spring-bed thrust bearing

The central support tilting thrust bearing is widely used in the motor-generator unit, and the central support tilting thrust bearing performs poorly compared with the offset bearing. In order to improve the performance of the thrust bearing capable of the bidirectional operation, a spring-supported switching tilting thrust bearing was designed, which could run under offset condition at both clockwise and counterclockwise. In order to verify the reliability of the bearing, we designed a true size thrust bearing test bench and measured the performance parameters of the temperature, pressure, oil film thickness, and power loss of the pad. This article introduces in detail the operation mechanism of the bidirectional offset spring-bed tilting thrust bearing. The bidirectional offset spring-bed tilting thrust bearing structure and the central support bearing structure were compared and tested. The test results of the performance difference of large tilting pad bearings with different structures were obtained. According to the experiment, the spring support structure has good adaptability, and the improved bidirectional offset support bearing not only has higher bearing capacity, but also has better performance in all aspects of temperature rise and loss than the central support bearing. The actual size experiment provides the experimental data for the theoretical calculation of large tilting pad bearings, providing a more accurate basis for the bearing performance and safety assessment.

Design of Tilting-Pad Journal Bearings Considering Bearing Clearance Uncertainty and Reliability Analysis

The dynamic characteristics of tilting-pad journal bearings (TPJBs) are strongly related to their geometric parameters, most importantly the bearing clearance. In turn, the bearing clearance in TPJBs is strongly dependent on the machining tolerances of the bearing parts and their assembling. Considering that, the machining tolerances of the pads can be of the same magnitude order of the oil film thickness in the bearing, it is uncertain that the TPJB will have the originally designed geometry after assembling. Therefore, the resultant dynamic characteristics of the TPJB also become uncertain. In this work, we present an investigation of tilting-pad bearings and their equivalent dynamic coefficients when subjected to dimensional variability. First, we perform a stochastic analysis of the system using a thermo-hydrodynamic (THD) model of the tilting-pad bearing and considering the bearing clearance in each pad as an independent random variable (varying between minimum and maximum values). We show that the scattering of the results of the dynamic coefficients is limited by the values obtained from TPJBs with all pads with maximum or minimum possible clearances. Second, we apply the concepts of reliability analysis to develop a design procedure for tilting-pad bearings. This design methodology considers the results obtained in the stochastic analysis and it allows the Engineer to appropriately design the bearing for a given probability of success or, inversely, a given probability of failure. Such approach assures a level of reliability to the dynamic coefficients of designed TPJBs in face of their dimensional variability.