Study on Cryogenic Hybrid Journal Bearings for Rocket Thrbopumps

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A hybrid bearing is a fluid-film journal bearing with characteristics of both hydrostatic and hydrodynamic bearings. The main advantage of hybrid bearings are small design size, good load capacity, a quasi-unlimited life (no observed wear), and the use of the process fluid for lubrication. By replacement of the self-lubricating ball bearings in the cryogenic turbopumps by the hybrid bearings, a significantly higher lifetime can be obtained and the inherent limitation of the rotational speed of the turbopumps can be widely extended in cryogenic rocket engines for future reusable launch vehicles (RLVs), where the lifetime of mechanical components is a critical issue. Therefore, experimental study on cryogenic hybrid bearings was carried out to develop the high performance hybrid bearings forcryogenic turbopumps.Test hybrid bearings were designed to operate at a rotational speed of up to 120,000 rpm based on the analytical results obtained from the conventional calculation method. The tes … More t bearing has a 60 mm diameter with L/D = 0.42, clearance/radius = 0.001, and 9 recesses. Rotating tests were carried out using the journal bearing test apparatus in Kakuda propulsion research center of JAXA. Liquid nitrogen is supplied to the test bearing with a pressure of about 5 MPa. Test results for the bearing with a 0.51 mm orifice diameter show that the self-excited vibration having a several times larger amplitude than that of the synchronous vibration was induced by pneumatic hammer instability due to cavitating flow of liquid nitrogen. However, the bearing with a 0.80 mm orifice diameter can be operated at the rotational speed of up to 50,000 rpm without any self-excited vibration. Comparison between the test results and the numerical predictions of rotordynamic coefficients based on the test conditions shows that instability induced by large cross-coupled stiffness coefficients due to fluid rotation is considered to onset at the rotational speed over 50,000 rpm.Therefore, a new hybrid bearing with a higher rotordynamic performance has been designed and manufactured based on the numerical predictions described above. Less