MODELLING ON PREDICTING PRESSURE DISTRIBUTION AND CAPACITY OF FOIL THRUST BEARING

Air bearing is future main supporting way of high-speed machinery such as turbocharger, micro gas-turbine engine. Foil bearing is a new type of air bearing which is lubricated by the thin-film air with its self-adapting elastic foil structure. It has many significant advantages such as non-pollution, longer working life, higher reliability, and lower friction loss. Different from foil journal bearing, in present the study of foil thrust bearing is extremely insufficient, especially about how to accurately predict the pressure distribution and efficiently improve the bearing capacity. The pressure distribution prediction of foil thrust bearing air film directly impacts the bearing stiffness and damping design, and then influences bearing capacity. The Reynolds equation commonly used to do such estimation is not accurate enough since the influence of temperature on air property parameters is ignored. The inaccurate prediction leads a catastrophic reduction to the bearing performance. In order to solve this problem, we propose a model to accurately predict the pressure distribution and capacity of foil thrust bearing using CFD method, as well estimating the relationship between air film clearance thickness, rotation speed, environment temperature and the capacity. Firstly, we simulate the pressure distribution of air film and then evaluate the simulation result by constrained experiments. We also correct the simulation by using modified air parameters obtained from experiment. The experimental results indicate our corrected simulation model is accurate with error less than 4%. Secondly, we compare simulation and experiment pressure results under different conditions. The model accuracy sensitivity varies within 10% under different rotation speed, air film clearance thickness and environment temperature. Finally, we use corrected model to analyze capacity impact parameters. We find the capacity of bearing increases with the decreasing of average air film clearance thickness under fixed speed of the thrust disc. The smaller clearance thickness is, the more influence its variation has on the bearing capacity. Meanwhile, the capacity of the bearing decreases with the reducing thrust disc speed under constant clearance thickness, and it decreases more obviously in the lower speed. The capacity reaches its largest under 200 C and it falls with the increases or decreases of environment temperature. The model in this paper provides important theoretical foundation when designing the stiffness, damping and temperature control of each bearing area.