Numerical Investigation of Turbopump Bearing Heat Generation in Liquid Methane

Liquid methane is one of the most promising candidates for the next-generation rocket propellant because it has an excellent balance between several propulsion performances such as specific impulse, storability, and structural coefficient. JAXA has developed rocket engine technologies for liquid methane engines. In this paper, we investigate heat generation characteristics of ball bearings used in liquid methane turbopumps. A usual approach to evaluate a cryogenic ball bearing performance is to conduct experimental testing which costs a lot. This research introduces numerical approaches based on physical mechanisms in rotating ball bearings to clarify the heat generation characteristics. The main factors of the heat generation are friction heat generation and fluid heat generation. The friction heat generation is caused by mechanical friction of bearing elements and calculated based on bearing motion analysis and Hertzian contact theory. The fluid heat generation is caused by the fluid drag force on bearing elements and calculated by CFD analysis. The theoretical model is compared with experimental results, showing an excellent agreement. It is clarified that the dominant factor of the bearing heat generation in liquid methane environment is the friction heat generation on races-balls contact at lower velocity condition while it tends to change to the fluid heat generation due to the bearing elements' rotational motion at higher velocity condition. In addition, cryogenic bearing characteristics which are clarified by theoretical modeling are discussed.