Start-transient testing of a hybrid (combined hydrostatic and hydrodynamic action) bearing supplied with air was completed, providing an indication of its performance while operating in a compressible fluid medium. The test start transients were modeled after Rocket Engine Transient Simulation Software (ROCETS) predictions for start-transient behavior of running speed ω(t) and bearing supply pressure P_s(t). The top test speed was 15 krpm. The ramp rate, supply pressure P_s values at 15 krpm, constant bearing unit load magnitude w_0, and load orientation (load-on-recess LOR or load-on-land LOL) were varied. Five different load-case combinations were carried out (separately) for LOR and LOL load configurations with ramp rates varying from 2206 rpm/s to 8824 rpm/s. The target pressures at 15 krpm varied from 5.32 bars to 18.25 bars. The tested bearing dimensions were: L = D = 38.1 mm, and C_r =0.0635 mm. Lift-off occurs due to the increase in P_s (ω dependent) and was defined as the point of departure towards the center of the bearing with increasing ω while the rotor remained 0.00254 mm (0.1 mils) above the bearing surface. This method is limited by the inability to accurately measure an established operating bearing clearance. Evaluation of the lift-off P_s versus applied unit load w_0 supports the following conclusions: (1) Lift-off P_s is approximately a linear function of w_0, (2) Changing the ramp rate while keeping constant the specified P_s at 15 krpm has no significant impact, (3) Lowering the limit P_s at 15 krpm may reduce the lift-off P_s value, and (4) The LOR start-transient cases required a higher lift-off speed and lift-off P_s values than the corresponding LOL start-transient cases.
展开▼
