Ansys-based air-bearing models and air-bearing systems for turbomachinery

Jiang, Tianchu (2022). Ansys-based air-bearing models and air-bearing systems for turbomachinery. University of Birmingham. Ph.D.

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Abstract

This thesis presents a PhD study that aims to improve the performance of air-bearing systems for turbomachinery applications, and develop simulation models for predicting the air bearing characteristics. A novel electromagnet (EM)-assisted system and a bearing support device are proposed. To facilitate the design of the proposed systems, ANSYS simulation models of fluid-structure interaction (FSI) are constructed to accurately analyse the dynamic and non-linear characteristics of grooved air bearings.

The novel EM-assisted system is designed to work with the hydrodynamic air bearings for two benefits: to reduce the lift-off speed and to improve stability. By lifting the rotor against gravity with the EM force, the lift-off speed is reduced by up to 48.39% with the tested herringbone-grooved air bearing. The function of improving the stability of the bearing-rotor system is achieved by applying an external static EM load. The onset speed of sub-synchronous vibration can be postponed by the enhanced static load on the rotor.

The novel support device for air-bearing systems is constructed by combining metal-mesh blocks and a squirrel cage. To control the required compression ratio, the metal-mesh blocks are inserted into a holder with predetermined dimensions. The squirrel cage structure, when combined with the metal-mesh blocks, provides the desired stiffness. This combination is capable of providing high damping capability while also providing adequate supporting stiffness.

The FSI simulation for grooved hydrodynamic air bearings is developed to accurately predict the air bearings’ performance. The model can evaluate the interactions between the rotor and the air film. Deformations caused by rotor bending, translation, and inclination movements are reflected in the three-dimensional air film model.

Both the EM-assisted system and the support device for air bearings are validated by experiments. The test rig of the EM-assisted system is built entirely from scratch in this PhD project. The rotor-bearing system, which includes grooved air bearings, is built using industry standards to investigate the material and fabrication requirements for high-speed air-bearing turbomachinery. Simultaneously, the simulation models are validated during the design of the proposed system and device.

In summary, this study presents accurate hydrodynamic air-bearing simulation models as well as effective methods for improving the performance of air-bearing systems. The aims of this research have thus been met.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):