Numerical investigation of slip flow phenomenon on performance characteristics of gas foil journal bearing

Abstract

Gas foil bearings (GFBs) are often employed in turbomachinery, particularly in high-speed turbochargers and turboexpanders. These bearings operate at very high speed and under very low clearance. On account of very low clearance, velocity slip can be observed at the gas-solid-interface. This paper investigates the effect of slip on various performance characteristics of the GFB. A model is put forth to predict the pressure and film thickness of a Gas Foil Journal Bearing (GFJB) used in helium-liquefaction turboexpander operating at 240 krpm. The present model addresses the slip at the gas-foil interface. Modified Reynolds equation, assuming first-order slip, is used along with the structural equation, which illustrates the compliant property of the foil. A numerical model is developed by finite difference approximation and solved by an iterative method. Various performance parameters are assessed for the no-slip and slip flow phenomenon in GFJB. The results are compared and a considerable difference is seen between the two models. The conventional Reynolds equation overestimates the load by approximately 8% at 240 krpm. The load-carrying capacity at different values of Knudsen number is also shown.

A Review on Modeling and Stability Aspects of Gas Foil Bearing Supported Rotors

“…The influence of slip-flow effect on the hydrodynamics of the GFBs has been investigated. Shahdhaar et al [70] included the slip-flow phenomenon in the GFJB model using the FD method. It was found that there was a decrease in the load-carrying capacity and an increase in the attitude angle with the inclusion of the slip-flow effect.…”