The instability caused by the fluid leakage leads to a limited performance of turbomachines. This instability may be improved by using flexible bearing supports with anisotropic stiffness. With a simplified model this effect is investigated including the influence of many parameters. The results show that the optimum range of anisotropy is strongly dependent on the parameters of rotor-bearing systems. In this paper an explanation from an energy point of view is presented to clarify the different stability behaviors with anisotropic bearing supports. Beside the simplified model, the stability of the complex rotor-bearing system with anisotropic bearing supports is investigated by the finite element model. An example of a typical 900 MW turbogenerator system is presented.

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