Due to the limitation of micro-machining technology, the bearing aspect ratio for a micro gas turbine is limited to a small value. Therefore, the load-carrying capacity of such bearing is inherently small. Thus, it is desirable to predict the load-carrying capacity as accurately as possible without being unnecessarily conservative. The direct numerical analysis of bearing characteristics was performed by mass conservation at coupled boundary. Journal bearing was numerically simulated for two cases −1) an externally pressurized bearing with four feeding holes and 2) a hydrodynamic bearing. Characteristics such as pressure distribution at the bearing surface, load-carrying capacity as a function of aspect ratio with a coupled boundary effects are investigated for micro gas turbine bearings. It is shown that a model of thrust and journal bearings coupled at boundary generally predicts a greater load-carrying capacity than uncoupled models.

Floating ring seals are widely used as a leakage control solution for turbomachines because they effectively operate with small clearances between the shaft and seal. The oxidizer pump of the 7 tonf liquid engine in the Korea Space Launch Vehicle II (KSLV-II) operates at high rotational speeds and under cryogenic conditions and has floating ring seals in the bearing cooling path to reduce leakages. In this study, we evaluated the frictional force acting on the nose of the floating ring in the oxidizer pump of the 7 tonf turbopump using numerical analysis, and we investigated the radial force on the floating ring induced by the vibration of the rotor and the flow characteristics around the floating ring seal. Through a comparison of the frictional and floating forces according to the change in the diameter of the floating ring noses, we also estimated the dynamic positioning of the floating ring. In addition, we examined the leakage of the floating ring seals with the rotational speed and gap size of the floating ring, and we used the results as data for designing a floating ring seal. Finally, we performed turbopump real-propellant tests with the floating ring seal of the high and the middle noses, finding that the test result was in good agreement with the results of numerical analysis.