Influence of slip-flow phenomenon on thermohydrodynamic behaviour of gas foil thrust bearings

Abstract

Gas foil bearings are often used in high-speed turbomachinery such as turboexpanders and turbochargers due to their merits over simple gas-lubricated bearings. The merits of gas foil bearings include their ability to tailor dynamic parameters such as stiffness and damping. Gas foil bearings usually have low clearance and operate at a high rotational speed, which eventually leads to velocity slip at the solid–fluid interface. This article investigates the effect of slip flow on various parameters of gas foil thrust bearings. A numerical model is formulated to predict pressure, film thickness and temperature distribution of helium lubricated gas foil thrust bearing at high rotating speed. The Reynolds equation is modified by assuming first-order slip coupled with the structural (compliant) and energy equation. The temperature-dependent viscosity and density of the fluid are also considered in the Reynolds equation to predict the thermohydrodynamic behaviour of gas foil thrust bearings. The numerical model thus developed uses a finite-difference method and the Newton–Raphson method to solve the Reynolds equation,whereas the successive over-relaxation method is used to solve the energy equation. Various performance parameters are compared for slip and no-slip conditions for gas foil thrust bearings. The results show a considerable difference between the two phenomena. Also, the conventional Reynolds equation tends to overestimate the load-carrying capacity.