Performance Evaluation and Comparison of Hybrid Rigid and Hybrid Foil Thrust Bearings

Abstract Foil thrust bearings have demonstrated significant potential as oil-free alternatives for use in high-speed turbomachinery, largely due to their adaptability to a wide range of environmental conditions. However, increasing the load capacity of foil bearings while maintaining high rotational speeds and minimizing wear remains a critical challenge. To address this limitation, hybridization of foil bearings has been explored by introducing externally pressurized air to maintain adequate bearing clearance. In this study, a performance comparison is conducted between a hybrid rigid thrust bearing (HRTB) and a hybrid thrust foil bearing (HFTB). Both bearings share an outer diameter of 82 mm, along with identical taper angles, orifice locations, and sizes. The performance evaluation was performed at 40,000 rpm under a hydrostatic pressure of 5 bar absolute. Key metrics such as mass flow rate, film thickness, and zero-speed performance were assessed. Additionally, power loss and load capacity were compared at zero and higher rotational speeds. The HFTB demonstrated a load capacity of about 400N at 40,000 rpm with a 5-micron average film thickness limiting criterion. In contrast, the HRTB exhibited pneumatic air hammering during dynamic testing, with the onset of this instability occurring earlier as rotational speed increased, accompanied by corresponding surges in torque measurements.