Robustness of Cryogenic Hybrid Journal Bearings

Abstract

In the present study, a nine-recess hybrid journal bearing (HJB) having a Young Leaf Mark recess was operated at a rotational speed of up to 75,000 rpm using the cryogenic journal bearing test apparatus at JAXA, to clarify an onset speed of the rotor instability supported by the cryogenic HJBs. Liquid nitrogen was supplied to the test bearing with a pressure of up to 4 MPa. The test bearing is 60 mm in diameter, 25 mm in width, with a 0.055-mm clearance and a recess area ratio of 0.186. When the HJB was operated at a rotational speed of over 74,000 rpm in liquid nitrogen, hard frictional contact between the bearing surface and the journal surface occurred, which consequently caused considerable damage to the Cr2O3 coating film on the journal. The results confirmed that the HJB surface damage had relatively little effect on HJB performance. Therefore, cryogenic HJB tested can be considered to have sufficient robustness when the rotational speed is below 60,000 rpm.

Keywords

• journal bearing
• cryogenic turbopump
• robustness
• rotordynamic performance
• liquid nitrogen