Predictions of Liquid Methane (LCH₄) Lubricated Hybrid Tilting Pad Journal Bearings for Reusable Rocket Turbopumps

This paper presents a performance analysis of a hybrid tilting pad journal bearing (TPJB) for reusable liquid methane (LCH₄) turbopumps. The numerical model incorporates temperature- and pressure-dependent density and viscosity of LCH₄ using fourth-order polynomial correlations based on the National Institute of Standards and Technology (NIST) data. A bulk-flow thermohydrodynamic analysis solves the Reynolds and energy equations considering turbulence, compressibility, recess inertia effects, and thermal mixing. The model calculates the pressure and temperature fields using the finite element and finite difference methods, respectively. The results of the static load and length-to-diameter ratio identify the available load range for the present bearing geometry. The cryogenic LCH₄ supplied through the recess locally suppresses temperature rise and produces spatial variations in its density and viscosity. The preload and radial clearance design can compensate for the limited load-carrying capacity of low-viscosity LCH₄, while they also can increase friction coefficient and temperature rise. The supply pressure ratio is the dominant parameter because it strengthens hydrostatic support and compensates for the weak hydrodynamic effect of LCH₄. In contrast, larger recess area weakens hydrostatic support and reduces dynamic coefficients. These results provide bearing-level design guidance for reusable LCH₄ turbopumps.