Abstract

Controllability in hydrodynamic bearings is gaining increasing attention to address the limitations of traditional passive designs. Most research in this area has focused on applying control to optimise dynamic characteristics in radial tilting-pad bearings, due to their significant impact on rotor dynamics. However, there is potential to implement control in hydrodynamic thrust bearings, where a major focus is to reduce power consumption. Such a device may be termed as a tribotronic system.

The proposed tribotronic strategy, evaluated in this work, is to control and optimise the wedge geometry of a tilting-pad thrust bearing for shearing loss reduction. A thermohydrodynamic model was developed to simulate the effects of actuated changes of the wedge geometry in response to force actuation through a lever arm. The force actuation provides a controlled moment to circumferentially tilt the pad out of its passive equilibrium state to a numerically determined optimal position for power loss reduction.

A proof-of-concept test apparatus was also developed, which facilitated comparison between passive and controlled operation of a novel controllable geometry tilting-pad thrust bearing. The developed bearing employs mechanical linear actuators to modify the wedge geometry and designed to operate in both passive and controlled states. The performance of passive and controlled operation was evaluated against a range of static performance characteristics including film thickness, film temperatures, friction torque, and power consumption.

Numerical and experimental results highlighted that the controllable bearing could reduce power consumption by around 12.8% compared to passive operation under the simulated operating conditions, whilst a trade-off reduction in minimum film thickness of 65% was numerically determined. Such trade-offs should be carefully managed within an autonomous control system to reduce the potential of surface contact.

Transient start and stop tests highlighted that controlled pre-tilt of the pads, prior to start-up, generated faster initiation of hydrodynamic lift and a maximum reduction of starting torque of 21.5% compared to passive operation for the simulated conditions. However, applying a pre-set landing tilt was also shown to be detrimental in terms of stopping-torque peak friction, compared to passive operation, whilst also leading to a longer period of mixed lubrication.

The main findings of this research highlight the potential of controllable pad solutions in tilting-pad thrust bearings for enhancing energy efficiency while also outlining some of the potential detrimental impacts this form of control may have on other relevant characteristics.