Session: 8.4 - Turbomachinery

Paper Number: 158104

158104 - Analysis of Oil-Air Two-Phase Flow in Thrust Bearing Spray System of a Large-Scale Hydro-Turbine Unit 

Abstract: 

The hydro-turbine is a type of turbomachinery that converts fluid energy into mechanical power, with the thrust bearing serving as the sole component responsible for supporting axial loads. The stability of the bearing’s load and lubrication performance are crucial to the stable operation of the hydro-turbine unit. The axial loads are supported by the oil film between the rotating collar and the stationary thrust pads, generating viscous friction that leads to heat buildup. This heat causes an uneven temperature distribution on the pads and deforms the pad surfaces, potentially compromising lubrication safety and leading to operational failures. The sprayed thrust bearing is a recently introduced technology. It consists of a nozzle and an oil-returning device that directs cooling oil onto the collar surface to reduce the temperature, while the heated oil is expelled through the return device. This spray system reduces the oil level in the oil tank, minimizing the losses caused by oil stirring in rotating components. In this study, a full 3D model of the sprayed thrust bearing was established for Computational Fluid Dynamics (CFD) simulations. The oil-air two-phase flow (OATP) method and thermo-hydrodynamic (THD) analysis method were used to investigate the spray lubrication conditions. By comparing the cases with and without the spray system, the characteristics of oil temperature, frictional losses, and vortex distribution within the oil tank were analyzed. The results show that the spray lubrication system can reduce the temperature of the oil film by approximately 2°C and decrease bearing stirring losses by 30%, thus improving the unit's operational efficiency. The OATP method provides a more accurate representation of the flow conditions within the bearing. When the bearing operates under rated conditions, an oil-gas interface forms at a 702mm oil level, with oil-air mixing occurring near the nozzle. The vortices within the oil tank were analyzed using the Q-criterion. While the spray system effectively reduces oil stirring, it also induces more chaotic flow, leading to the formation of vortices between the bearing pads. These vortices contribute to energy dissipation, increasing the energy losses of the bearing. These findings highlight the significant impact of the spray structure on the flow characteristics, temperature distribution, and frictional losses of the thrust bearing. It is beneficial for improving the lubrication performance and reliability of the bearing, as well as enhancing the efficiency of the unit. Moreover, numerical simulations of the spray system provide valuable insights for optimizing the spray structure.

Keywords: Thrust bearing, Hydro-turbine unit, Turbomachinery, Oil-air two-phase flow, Thermo-hydrodynamic analysis

Presenting Author: Yishu Shi Department of Energy and Power Engineering, Tsinghua University, China

Presenting Author Biography: I am a PhD student from Tsinghua University, specializing in the thermo-hydrodynamic research of bearings in hydro-turbine units.