The analytical oil film force model for floating ring seal is established including the effect of axial pressure gradient.The analytical model is based on the oil lubricated Reynolds equation and the short bearing assumption, where the fluid Lomakin effect is considered. The pressure distribution of the floating ring and static characteristics is studied by numerical simulation. The three dimensional flow model is established and solved by the CFD method. By employing the finite element method, the dynamic model of the floating ring seal-steam turbine rotor system is established. The critical speed, mode shape and dynamic response of the steam turbine rotor with different bearing support stiffness are obtained. The effect of the floating ring oil film force on the critical speed and instability speed with different bearing support stiffness is studied. The effects of floating ring parameters (groove geometrical dimensions) on dynamic response are studied, and the stability of floating ring seal-rotor system with variation of the factor is analyzed. The floating ring seal can play the role of increasing the supporting effect, which will increase the critical speed of the rotor system. The floating ring seal can cause the sub. synchronous vibration and the groove can significantly increase the stability of system.
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