Research On Dynamic Characteristics Of Floating Ring Seal-rotor System

With the rotating machinery developing towards to the direction of high speed,high efficiency, large span, high power and pressure difference on both sides of thefloating ring seal increasing, the nonlinear dynamic characteristics of floating ringseal-rotor system are becoming increasingly prominent. The traditional researchmethods of floating ring seals usually use linear small perturbation theory to analysisand design, but the nonlinear characteristics of the system have not been well described,and thus they have certain application limitations. Therefore, it has great significance toestablish the nonlinear oil film force model of the floating ring seal in researching onthe nonlinear dynamic characteristics of the floating ring seal-rotor system. In responseto these issues, the nonlinear oil film force model of the floating ring seal wasestablished by studying the floating ring seal structure, working principle and forcesituation. Numerical simulation of the nonlinear dynamic characteristics of the floatingring seal-turbine rotor system was conducted with this mode, and the main contents areas follows:Based on the small clearance film lubrication Reynolds equation, the nonlinear oilfilm force model of the floating ring seal was established. Pressure difference on bothsides of the floating ring seal and Lomakin effect of the gap entrance were consideredand assumptions were similar to the short bearing. Meanwhile, numerical simulation ofpressure distribution and static characteristics of the floating ring were conducted.Three-dimensional model of the floating ring was established, on this basis, theflow field of grove floating ring clearance was studied by numerical simulation. Theeffects of geometric dimensions and pressure difference on pressure distribution of thefloating ring were analyzed. In addition, the effects of eccentricity and groove on thefloating ring seal leakage were studied by numerical simulation. The results show thatthe floating ring leakage increases with increasing eccentricity, and the groove canreduce the leakage. Moreover, the leakage reduces with the deep to width ratioincreasing, when the deep or width is constant.Based on the floating ring oil film force model, the floating ring seal-turbine rotorsystem dynamics model was established, which combined with the finite element theory,and the numerical simulation of this model was conducted. The critical speed, modalshapes and dynamic response under different support stiffness were obtained;furthermore, the effects of floating ring seal on the critical speed and stability of turbinerotor were studied.Based on the floating ring seal-turbine rotor system dynamics model, the effects ofstructural parameters (aspect ratio, clearance ratio, oil viscosity and grove geometricdimensions) and pressure difference on dynamic response were studied, and the stability of floating ring seal-rotor system with variation of each factor were analyzed. Theresults show that appropriate to reduce aspect ratio and lubricant viscosity or increaseclearance ratio and pressure difference will increase the stability of the floating ringseal-turbine rotor system. The groove can significantly increase the stability of system,and the stability of system improves gradually with grove increasing.