EFFECTS OF CONICAL CAVITY ON THE LOAD CAPACITY OF EXTERNALLY PRESSURIZED STEAM-LUBRICATED JOURNAL BEARING

Motivated by the urgent need for the development of oil-free and closed-loop turbomachinery in deep-space and deep-sea exploration missions, process-gas lubricated bearing has seen the recent surge of interest due to its numerous advantages. Particularly, externally pressurized steam-lubricated bearing plays an important role in closed-cycle steam turbine, which significantly influences the machine reliability and operating characteristics. In order to achieve effective lubrication and obtain high load capacity, a full understanding of how bearing geometrical parameters and gas properties affect the bearing overall performance is required. This study mainly proposes a novel design to increase the load capacity of the externally pressurized steam-lubricated journal bearing. Firstly, the correctness of simulation is verified based on a simple bearing model. And with the help of the computational fluid dynamics numerical tool, this paper conducts a detailed fluid flow and heat transfer analysis for inherently compensated steam journal bearing. The computations have been performed for two different gases-air and steam. The bearing diameter is 110mm and it has single-row 8 orifices. Flow field parameters such as pressure distribution, mass flow rate, velocity distribution are presented. Results also reveal the classical pressure depression in the gas film entrance and transonic flow phenomenon in the bearing clearance. Second, based on the lubrication flow analysis, a new conical cavity concept is presented. The study compares the static load capacity performance and flow characteristics of the steam journal bearing with and without the conical cavity. We find that the conical cavity structure can actually improve the static load capacity of the inherently compensated bearing. Finally, the influence of conical cavity angle on the load capacity and mass flow rate is investigated. There are 11 different conical cavity angles which vary from 20 degrees to 70 degrees. The numerical results show that the conical cavity angle almost has no influence on the static load capacity but reduces the mass flow rate when the angle value rises. This study demonstrates that how to design the high load capacity externally pressurized steam-lubricated journal bearing for closed-cycle steam turbine.