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.

A review of thermohydrodynamic aspects of gas foil bearings

“…A separate numerical analysis was also conducted which shows forced convection in bump channels is an effective approach for better cooling at high loads. Much recently, Kumar et al 101 investigated the impact of slip flow phenomenon on THD behaviour of GFTB. The model includes the use of first-order slip velocity (equation ( 18)) at the solid-fluid interface and thus modifies Reynold's equation.…”

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

“…A negligible effect was observed in the parameters like torque and power loss due to the slip flow. Subsequently, Kumar et al [72] incorporated the slip-flow effect in in a GFTB model and presented a modified Reynolds equation with the first-order slip condition. It was observed that the traditional Reynolds equation has a bias towards overestimating the load-carrying capacity of the GFTB.…”

The fluid-thermal-structural interaction analysis of a new multifoil aerodynamic thrust bearings

“…It was found that the thermal expansions of the rotor and bearing structure were the main cause of TEI. Kumar 23 established a model of helium gas lubricated thrust bearing and compared the difference in the gas foil thrust bearing thermal characteristics under slip and no-slip conditions by finite difference method. Liu 24 compared and analyzed the effects of the rotating speed, bearing load and cooling airflow on the thermal distribution of foil gas bearing through experiments and simulations.…”