Measured and Predicted Temperature Differentials Within a Rotor at a Tilting-Pad-Journal Bearing Associated With the Morton Effect

Abstract

The current work shows the implementation of a high-speed turbomachinery test rig to measure vibration and internal shaft temperature differentials at a journal bearing for a rotor system designed to induce the Morton effect rotordynamic phenomenon. The vibration and shaft temperature measurements are compared to predictions using an analytical code described by Tong and Palazzolo [6,7]. An existing high-speed test rig was adapted, including a new rotor with six equally-spaced RTDs embedded at the journal bearing centerline. The rotor configuration included an overhung rotor design with a 58 mm (2.3 inch) diameter, 5-pad tilting-pad journal bearing. The in-rotor temperature measurements were conditioned using a custom on-board amplifier and extracted with a high-speed commercial slip ring. Test conditions included various levels of unbalance, bearing oil inlet temperature, and operating speed. Test measurements show that the temperature differential across the shaft is dependent upon operating speed, as well as vibration amplitude. Operating conditions included rotational speeds up to 19.5 krpm and vibration levels approaching the magnitude of the bearing clearance. Testing near the rotor first lateral natural frequency (or critical speed) with a high level of initial unbalance resulted in the highest temperature differentials across the shaft of approximately 11 °C (20 °F) plus. Vibration measurements show hysteresis in the synchronous vibration response in the Bode and polar plots. This measured vibration hysteresis is consistent with the rotor hot spot or temperature differential changing the unbalance level of the rotor. Overall, both the test measurements and predictions show notable temperature differentials and hysteresis behavior in the vibration response that are believed to be associated with the Morton Effect. These conditions are considered precursors to the spiral vibration or fully developed synchronous instability typically associated with the Morton Effect.