Effect of journal out-of-roundness on stability of a symmetric hydrodynamic journal bearing system. Part 2: Experimental investigation

Part 2 of the study furthers the research and aims to present evidences from an experimental investigation. The work presents the experimental research with a rig for examining the effect of journal out-of-roundness on the dynamic performance of a symmetric hydrodynamic journal bearing system. Four shafts with different magnitudes of journal out-of-roundness were fabricated for the experiment. The test rig was equipped with a date logging system to collect and process all signals provided by the displacement probes and the thermocouples. The onset speed of oil film instability was determined by analysing the spectrums of the journal vibrations. The experiments show a notable double-synchronous frequency vibration component incurred by the journal out-of-roundness, which makes the system behave as oil whirling but the mechanism is different. The results also coincide with the theoretical calculations presented in Part 1 of the study, which validates that the journal out-of-roundness may increase the overall system stability when the dimensionless out-of-roundness is below 0.4, but vibration levels increase. The study can help engineers to choose reasonable tolerances or enable systems with certain manufacturing tolerances to operate within a more stable range.