Analytical study on hybrid thrust foil bearing, structural characterization and measurement of static performance

Abstract

This work presents a novel hybrid foil thrust bearing (HFTB) with an outer diameter of 154 mm, along with simulation and test results. The HFTB incorporates a high-pressure air/gas injection to the taper portion of the thrust foil bearing, boosting the hydrodynamic effect on the main bearing surface and hydrostatic load capacity at zero speed. The bearing has high load capacity, low power loss, and no friction/wear during startup and shutdown. Firstly, push-pull tests were conducted on a double-acting HFTB configuration to evaluate the nonlinear structural stiffness of the bump foil structure. The measured nonlinear stiffness model was adopted to predict the overall bearing performance under various speeds and loads. The simulation uses an advanced model which predicts the 2D plate top foil deflection with physical bump locations mapped from the actual hardware. The simulation confirms that the hybrid operation significantly increases the load capacity compared to hydrodynamic bearing due to the boost effect of hydrostatic pressure in the main film. Tests were conducted at 10krpm, 15krpm, and 20krpm to measure load capacity, power loss, and average film thickness. At 20krpm, a maximum axial load of 1711 N was achieved before bearing failure. Ultimately, the novel HFTB shows excellent static performance with potential for use in Organic Rankine Cycle (ORC) generators and other large oil-free turbomachines.