Rotordynamic Performance Measurements and Model Predictions of Water-Lubricated Journal Bearings with Different Radial Clearances

Abstract

This study develops a test rig to investigate the rotordynamic performance of a rotor system supported by water-lubricated journal bearings. The test evaluates the vibration response under the different radial clearances of bearing and validates the analytical data through experimental comparison. Test bearings have a diameter of 12 mm, length of 12 mm and radial clearance 35, 70 μm. The test conditions included rotor speed from 0 rpm to 6,000 rpm and supplied water temperature 20℃. Analysis results indicate that increasing rotational speed and clearance reduces the damping ratio, leading to higher rotor instability. As the clearance increases, the bearing damping performance deteriorates, causing a rise in 1X vibration amplitude near the critical speed and the dominance of 0.5X subsynchronous components. Test results agree well with analytical predictions, demonstrating the accuracy of the predictions. Furthermore, smaller clearance enhances direct stiffness and damping, which increases the system's natural frequency and improves rotor stability. Note that bearing clearance significantly affects the dynamic response and an appropriate reduction in clearance can improve stability of water lubricated bearing supported rotor systems. The verified predictive model allows for parameter studies and the optimization of the bearing-rotor system design to increase stability and reliability.