Tilting pad thrust bearings are the key components in hydropower units. As the thrust loads increase with the unit capacities of the hydro turbines, many thrust bearings failed due to rub-impacts between the collar and pads. Some plants have to be shut down for up to one month to repair the damaged pads which has lead to enormous economic losses. The lubrication processes of thrust bearings are quite complex involving fluid-thermal-structural interactions between the pad, the collar, the oil film and the oil surrounding the pad. This paper reviews the bearing mechanism including the thermal-elastic deformation, the transient and dynamic characteristics, the bidirectional thrust bearing, as well as the various prediction methods on the lubrication performance. At last, an overview of some special designs including the covered materials, supporting system and hydrostatic jacking system to improve the thrust lubrication was briefly presented.

A review on the large tilting pad thrust bearings in the hydropower units

Polymer-based additives such as poly isobutylene are blended with lubricating oil to enhance the lubricating performance of the base oil. The Rabinowitsch fluid model effectively describes the infl...

Performance of hydrostatic circular thrust pad bearing operating with Rabinowitsch fluid model

The pressure distribution in an aerostatic bearing has an important effect on the performance of the associated mechanical equipment. To more accurately predict performance, a new dynamic modeling ...

A novel dynamic modeling method for aerostatic spindle based on pressure distribution

Reynolds equation is solved using finite difference method (FDM) on the surface of the tilting pad to find the pressure distribution in the lubricant oil film. Different pressure profiles with grid independence are described. The present work evaluates pressure at various locations after performing a thorough grid refinement. In recent similar works, this aspect has not been addressed. However, present study shows that it can have significant effect on the pressure profile. Results of a sector shaped pad are presented and it is shown that the maximum average value of pressure is 12% (approximately) greater than the previous results. Grid independence occurs after 24 × 24 grids. A parameter "ψ" has been proposed to provide convenient indicator of obtaining grid independent results. ψ = |(P refinedgrid - P Refrence-grid)/P refinedgrid|, ψ ≤ e, where "e" can be fixed to a convenient value and a constant minimum film thickness value of 75 μm is used in present study. This important parameter is highlighted in the present work; the location of the peak pressure zone in terms of (r, θ) coordinates is getting shifted by changing the grid size which will help the designer and experimentalist to conveniently determine the position of pressure measurement probe.

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Numerical Investigation of Pressure Profile in Hydrodynamic Lubrication Thrust Bearing.

Investigation on the angular displacements influence and nonlinear effects on thrust bearing dynamics

Determination of a large tilting pad thrust bearing angular stiffness

In this paper the non dimensional load parameter, volumetric flow rate, energy flux, oil film temperature and power loss of a large thrust pad bearing are formulated. The objective of the paper is to determine the novel non dimensional thermal, volumetric and power loss parameters in addition to the known load and energy flux parameters of the bearing. The computation is done by formulating and numerically solving the oil film thickness, two dimensional Reynolds’, Vogel-Cameron and energy equations at the different nodes of the pad oil film using a finite difference procedure. The lower the degree of the objective shape polynomial more is the accuracy of the slider bearing shape and pressure distribution. The developed derives the value of ‘a’ for which the load is maximum. The variation of the dominant bearing centre of pressure with respect to the corresponding values of ‘a’ is studied. From the equation of fluid film temperature the minimum rise in bearing temperature corresponding to the values of ‘a’ are determined. The oil film temperature distribution results are found satisfactory in terms of computer time and convergence criteria. The accuracy of the results is thoroughly validated by the variation of the load and thermal contours. This data and analysis serves as an input for rotor dynamic studies and includes the scope to develop safe operation of the bearing at high speeds in vertical hydro-electric rotors. Evaluation of Operational Characteristics in a Large Thrust Bearing

Evaluation of Operational Characteristics in a Large Thrust Bearing

In this paper the non-dimensional load, volumetric flow rate, energy flux, oil film temperature and power loss parameters of a tilting-pad thrust bearing are formulated. The objective of the paper is to determine the novel non dimensional thermal, volumetric and power loss parameters in addition to the load and energy flux parameters of the bearing. The computation is done by formulating and numerically solving for the oil film thickness, two dimensional Reynolds’, Vogel-Cameron viscosity-temperature relationship and energy equations at the different nodes of the oil film using a finite difference procedure. The planar film shape polynomial ensures the accuracy of the slider bearing shape and pressure distribution. The numerical procedure evaluates the value of ‘a’ at which the load is maximum. The variation of the bearing centre of pressure with respect to the corresponding values of ‘a’ is studied. From the fluid film temperature equation the rise in bearing temperature corresponding to the range of ‘a’ values is determined. The oil film temperature distribution results are found satisfactory in terms of computer time and convergence criteria. The accuracy of the results is validated in the variation of the load and thermal contours. A mesh independence test is conducted using three meshes of different sizes. The mesh independent solution and convergence is obtained for the smallest mesh that also reduces simulation run time. This data and analysis serves as an input to determine the dynamic stiffness and damping coefficients. It includes the scope to develop a design method for safe operation of the bearing at any speeds in vertical hydro-electric rotors.

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Kaushal K. Chaturvedi

Papers

Determination of a large tilting pad thrust bearing angular stiffness

Evaluation of Operational Characteristics in a Large Thrust Bearing

Theoretical Evaluation of the Operational Characteristics in a Large Thrust Bearing