| As a typical radial clearance seal,the sealing surface of floating ring seal is filled with thin fluid film to separate the floating ring from the rotor.Owing to the well feasibility for high-pressure and high-speed working conditions as well as smaller leakage rate compared to the fixed clearance seal,floating ring seals have been widely applied to liquid rocket engines,centrifuges,aero-engines and so forth.However,recent development of large-thrust,reusable rockets and large-scale multifunctional centrifuges,poses great challenges for designing floating ring seals with high reliability,long life-time and well adaptability for variable working conditions.Aiming at the application requirements for high-pressure,high-speed,variable working conditions and reusable dynamic seals,a novel hybrid floating ring seal with throttle orifices(HFRS)is proposed in this thesis.The key innovation of HFRS is to guide the sealing medium into the radial clearance through the throttle orifices,which produces the hydrostatic bearing effect without external conditions.Consequently,the bearing performance of floating ring seals is significantly improved.HFRS has outstanding advantages in load capacity and stability in comparison to the traditional straight hole type floating ring seal(FRS),which is expected to deal with the problem of rub-impact due to insufficient low-speed bearing capacity in the traditional floating ring seals.Aiming at the bearing-characteristics calculation for HFRS,a fluid film bearing capacity model is proposed considering factors such as the influence of orifices,Lomakin effect,turbulent flow and fluid compressibility.The flow term of orifices and the inlet pressure loss term is introduced into the presented model to make it suitable for the bearing capacity calculation of HFRS.The simulation results based on the proposed model show that HFRS has larger low-speed load capacity and smaller attitude angle in comparison to FRS,and excellent bearing characteristics can be expected.The mechanism of the well performance lies in the introduction of the hydrostatic bearing effect that significantly increases the radial component of bearing capacity and thus reduces the tangential component.Aiming at the dynamic-characteristics calculation for HFRS,a nonlinear dynamic model is also established by considering the influence of factors such as the dynamic bearing capacity of the floating ring seals,the friction force on the end face,and the additional resistance of the fluid to the floating ring.The three working states of floating ring seals,namely lock-up,synchronous whirl and half-speed whirl,can be accurately predicted based on the proposed theoretical model.Aiming at the leakage-characteristics calculation for HFRS,a leakage rate model is established by considering the influence of orifices,Lomakin effect,operation parameters,and flow state.The theoretical results show that the leakage rate of HFRS is slightly greater than that of FRS.And the theoretical results of the leakage rate are consistent with the experimental results.At last,a seal test rig is developed to verify the proposed model and design presented in this thesis.The dynamics characteristics and leakage rate of HFRS and FRS are measured simultaneously.The experimental results have confirmed that the HFRS has excellent bearing-characteristics and leakage-characteristics,and it is consistent with the theoretical analysis results.Because of its excellent bearingcharacteristics and lower leakage rate,the designed HFRS has been successfully applied to several scientific devices such as multifunctional centrifuges,and is expected to be applied in liquid rocket engines and aero engines in the future. |
