Circumferential film thickness measurement in journal bearings via the ultrasonic technique

A key parameter in hydrodynamic journal bearing performance is lubricant layer thickness around the circumference of the shaft-bearing interface. In the present work, the ultrasonic amplitude, phase change and resonant dip techniques are applied to obtain circumferential film thickness profiles in a bespoke journal bearing test platform under a range of shaft-aligned, shaft-misaligned and shut-down operating conditions. Film thickness results are compared against the Raimondi-Boyd theoretical prediction model and eddy current sensor measurements. By using an on-line referencing technique, the amplitude and phase change models demonstrated high accuracy for thin films and the resonant dip technique enabled film measurements within the bearing thick film region. Thus, applying the three methods simultaneously allowed analysis of lubricant films around the bearing circumference.