Finite Element-based Study on Lubrication Characteristics and Parameter Optimization for Thrust Bearings in Hydroelectric Generator Units

YANG Ziyi; XUE Bing; XU Bo; LI Yongbo; ZHANG Zhi; XIANG Aijun; WANG Youqiang

doi:10.16490/j.cnki.issn.1001-3660.2025.23.010

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Surface Technology ›› 2025, Vol. 54 ›› Issue (23) : 141-155. DOI: 10.16490/j.cnki.issn.1001-3660.2025.23.010

Finite Element-based Study on Lubrication Characteristics and Parameter Optimization for Thrust Bearings in Hydroelectric Generator Units

YANG Ziyi¹, XUE Bing^2,3, XU Bo^2,3, LI Yongbo^2,3, ZHANG Zhi^2,3, XIANG Aijun^2,3, WANG Youqiang^1,4,*

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Abstract

The work aims to investigate the lubrication characteristics of the thrust bearing in a hydroelectric generator unit, exploring the impact of water contamination in lubricating oil on its fundamental physical properties. The oil film characteristics and pad deformation under basic operational parameters were analyzed and the key operating parameters were optimized to enhance the reliability and operational efficiency of the bearing. Through experimental testing of physical properties, the viscosity, density, specific heat capacity, and thermal conductivity of the lubricating oil with varying water contents were measured. A numerical model of elastohydrodynamic lubrication (EHL) incorporating bidirectional fluid-structure interaction was established through COMSOL Multiphysics to simulate the oil film pressure distribution, thickness, and pad elastic deformation under basic operational conditions. Orthogonal experimental design was employed to analyze the effect of rotational speed, load, tilt angle, and water content on the lubrication performance. Range analysis and variance analysis were conducted to determine the significance of each parameter and identify the optimal operational combination.
The results of the physical property tests revealed that water incorporation significantly affected the properties of the lubricating oil. For density and thermal conductivity, the values were the lowest for pure oil and increased with the increasing water content. For dynamic viscosity, at temperatures below 308 K, the viscosity of low-water-content oil (5 g/L) decreased by 14.4% compared to that of pure oil, while high-water-content oil (100 g/L) exhibited viscosity approaching that of pure oil. At temperatures above 308 K, the viscosity-temperature sensitivity of all water-content systems converged, indicating that elevated temperatures could markedly mitigate the impact of water content differences on viscosity. For specific heat capacity, increasing water content generally raised the value, but an anomalous trend was observed in the 5 g/L system.
Numerical simulations under basic operational conditions demonstrated that the oil film pressure exhibited a ring-shaped distribution characterized by "high center, low periphery" with a maximum pressure of 8.460 8 MPa concentrated near the outer diameter of the trailing edge of the pad. The minimum oil film thickness was 98.716 μm, primarily distributed along the trailing edge. The thrust pad displayed a concave deformation pattern at the center, with a maximum elastic deformation of 2.69 μm, accounting for only 2.72% of the minimum oil film thickness, thus exerting a negligible effect on lubrication performance.
Range analysis of the orthogonal experiments indicated that load was the dominant factor affecting the maximum oil film pressure and the maximum elastic deformation, while rotational speed played a primary role in determining the minimum oil film thickness. Trends in the mean values of the maximum oil film pressure, the minimum oil film thickness, and the maximum elastic deformation with respect to each factor level were examined. The results showed that higher rotational speeds or lower loads and tilt angles significantly reduced oil film pressure and elastic deformation while increasing the minimum oil film thickness. Water content exhibited a nonlinear effect, with oil film pressure and deformation minimized at 5 g/L, while oil film thickness peaked at this level. Variance analysis corroborated the range analysis results, further validating the reliability of the significance conclusions. The orthogonal optimization yielded an optimal operational combination of 135 rpm rotational speed, 1 450 kN load, 0.003° tilt angle, and 5 g/L water content, under which the maximum oil film pressure decreased to 7.430 6 MPa and the minimum oil film thickness increased to 133.22 μm. Slight water contamination showed no significant impact on thrust bearing lubrication performance, and the optimized parameter combination markedly enhanced lubrication performance. This study aims to provide a theoretical foundation for improving the operational reliability of thrust bearings and holds practical engineering value for ensuring the safe and efficient operation of hydroelectric units.

Key words

thrust bearing / elastohydrodynamic lubrication / lubrication characteristics / water contamination / finite element analysis / orthogonal experiment

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YANG Ziyi, XUE Bing, XU Bo, LI Yongbo, ZHANG Zhi, XIANG Aijun, WANG Youqiang. Finite Element-based Study on Lubrication Characteristics and Parameter Optimization for Thrust Bearings in Hydroelectric Generator Units[J]. Surface Technology. 2025, 54(23): 141-155 https://doi.org/10.16490/j.cnki.issn.1001-3660.2025.23.010

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