Prediction of static characteristics of cryogenic hybrid journal bearing for reusable pump-fed liquid rocket engine by computational fluid dynamics simulation

The utilization of reusable rockets presents a promising design solution for the reduction of space transportation costs. The maintenance of turbomachinery is a costly process. Of these, the bearings of the turbopump are among the most critical components. Hybrid bearings, which combine hydrostatic and hydrodynamic bearing technologies, are regarded as a particularly promising solution for rocket propulsion systems. The objective of this research was to conduct a numerical analysis that would contribute to the development of cryogenic hybrid bearings, which can enable stable and wide-ranging operations. Three-dimensional computational fluid dynamics simulations were conducted for the tested journal bearings, based on Reynolds-averaged Navier-Stokes simulations with sub-models accounting for the effects of turbulence and cavitation. The static characteristics of high-speed hybrid bearings were investigated with the geometry for liquid methane in the University of Pisa. A series of simulations was conducted to investigate the inlet and outlet pressure ratios and flow rates, which are important parameters representing the characteristics of journal bearings. These simulations were performed with varying shaft eccentricity conditions. Moreover, the simulation results revealed that internal flow within the narrow clearance of the hybrid bearings is a key factor in the occurrence of cavitation and its subsequent impact on bearing performance. Furthermore, the impact of cavitation on the pressure distribution and fluid force was evaluated by comparing the results with and without consideration of cavitation occurrence. We clarified that the cavitation model had a significant influence on the results of the performance prediction.