Side Load Effect on Turbomachines with AMB

Turbomachinery bearing systems are normally designed for radial loads corresponding to the weight of the rotor. Nonuniform pressure distribution around the wheel(s) of a turbomachine may also contribute to the magnitude of gas dynamic radial load, called side load. Conventional oil bearings have such a comfortable margin of load capacity that dynamic load is not of any design significance. Active Magnetic Bearing (AMB) systems have limited load capabilities. Turbomachinery manufacturers have developed their own methods of calculating side load. When the magnitude of side load exceeds the AMB' s capacity, several corrective actions are available. AMB applications for off-shore platforms or dew point control of natural gas using lurboexpanders are on the rise. Process gas pressures of these applications are in the range of 60-100 Bar and the side load effect is significant for high density process gas or liquid if turbomachine components are not designed correctly. Therefore, it is essential to use Computational Fluid Dynamic (CFD) to calculate the flow field in the casings. Corrective action should not sacrifice turbomachine performance which may result in a less desirable market for AMB. In this paper, the authors present one method of side load calculation and its theoretical background. In conclusion, the merits of alternative solutions are discussed.