Static Performance of a Hydrostatic Thrust Foil Bearing for Large Scale Oil-Free Turbomachines

This work presents a novel design of a hydrostatic thrust foil bearing (HSTFB) with an outer diameter of 154mm along with simulation and test results up to specific load capacity of 223kPa (32.3psi). The HSTFB incorporates high pressure air/gas injection to thrust foil bearing with uniform clearance. This bearing has large load capacity, low power loss, and no friction/wear during startup and shutdown. In addition, the HSTFB allows bidirectional operation. The paper also presents advanced simulation model of foil deflection adopting exact locations of the tangentially arranged bumps to the cylindrical two-dimensional plate model for top foil. This method predicts foil deflection with better accuracy than traditional independent elastic foundation model which distributes the location of bumps over the nodal points in cylindrical coordinate, and with less computational resource than finite element method applied to entire bump/top foils. The presented HSTFB, was designed for Organic Rankine Cycle (ORC) generators, but performance was predicted and measured using air in this paper. The bearing static performance is compared analytically against the rigid counterpart, and presented at different supply pressures, speeds, and minimum film thicknesses. Experimental verification is performed at 10, 15 and 20krpm. The measured load capacity and frictional loss agree well with the prediction. The measured film thickness also agrees with measurement after compensation of structural deflection of the thrust runner disc. Overall, the novel HSTFB demonstrates excellent static performance and shows great potential for adoption to the intended ORC generators and other large oil-free turbomachines.