LUMEN Turbopump: Preliminary Thermal Model

Abstract

The DLR LUMEN (Liquid Upper stage deMonstrator ENgine) rocket engine comprises of two separate turbopumps, one each for Liquid Oxygen (LOX) and Liquified Natural Gas (LNG) supply. In both turbopumps, an identical bearing block separates the pump section from the turbine section. In the current design, the bearing block features an oil-jet lubrication system to cool and lubricate the bearings during operation. Cryogenic conditions at the pump-interface and high temperature conditions at turbine-interface impose thermal constraints on the selection of a suitable lubricant for the bearing assembly and the design of the lubrication system. As a starting point to address this challenge, this paper presents a preliminary uncoupled finite element thermal model of the LUMEN LOX turbopump. The thermal model investigates the thermal behavior of the housing and rotor components in the bearing housing from start-up to shutdown of the turbopump. The model employs thermal worst case conditions to establish the operational thermal envelope of the turbopump system. Spatial and temporal evolution of the temperature at critical points within the bearing housing are reported. The model, albeit the uncertainties rooted from its empirical nature, provides beneficial insight into the thermal characteristics of the turbopump assembly. This serves as a first estimate of the thermal constraints for the selection of lubricant oil.