Fluid Cavitation And Inertia Effects In Spiral-grooved Face Seals Under High-speed Conditions

Spiral-grooved face seal operates in the non-contacting state due to the hydrodynamic effect.It is widely used in petroleum and petrochemical industry,aerospace and other fields due to the good load-carrying capacity,high reliability and long service life.With the development of power machinery toward the high-speed or ultra-high-speed conditions,the problem of high-speed mechanical seals is becoming more and more prominent.Cavitation and fluid inertia are the common fluid mechanical phenomena for the lubrication flow in the sealing gap at high-speed conditions and play important roles in sealing performance.The study on the cavitation and fluid inertia in the spiral-grooved face seals at high-speed conditions not only enriches its design theory,but also meets the requirements of Made in China 2025-Energy Equipment Implementation Plan and CMES for developing high-parameter mechanical seals and overcoming key common technologies.It is of great significance to the development of national energy and aerospace.In the dissertation,firstly,based on the Reynolds equation with the JFO cavitation theory,the lubrication model of spiral-grooved face seals is developed and solved by the Galerkin(SUPG)finite element method.The influencing mechanism of cavitation in the spiral-grooved face seal is revealed under the hydrodynamic lubrication.It deepens the cognition of the influencing mechanism of cavitation on the fluid flow in the sealing gap.The concept of the cavitation suction effect of lubricant film is proposed and the cavitation suction mechanism of controlling the leakage is revealed.Further,a cavitation suctioning face seal is designed and the numerical results indicate that it has good reverse suction performance and hydrodynamic load-carrying capacity.It can be popularized and applied in engineering practice.Aiming at the fluid inertia effect at high-speed conditions,based on the fluid lubrication theory and JFO cavitation theory,a set of lubrication governing equations are presented to govern the fluid flow affected by the cavitation and fluid inertia in spiral-grooved face seals.They are numerically solved with the combination of the SUPG finite element method,artificial numerical dissipation technique and Newton-Raphson method.The theoretical model and numerical algorithm are validated by comparing with the results of the 3D flow field simulation.The effects of the cavitation,centrifugal inertia and convection inertia on the performance for the spiral-grooved face seal are analyzed at high-speed conditions under the hydrodynamic lubrication and the coupling mechanism of the cavitation and fluid inertia is revealed.The cognition of the fluid inertia is deepened,and the performance variation regularities influenced by the above effects in the spiral-grooved face seal are obtained.Considering the viscous heat generation in the lubricant film at high-speed conditions,based on the above theoretical model and fluid viscous-temperature characteristics,a mathematical model of the thermohydrodynamic lubrication including the rotator,stator and lubricant film is developed for spiral-grooved face seals.The finite element method is applied to solve the quasi 3D energy equation of lubricant film,the 3D heat conduction equations of the rotator and stator and the lubrication equations considering the cavitation and fluid inertia effects.Under the thermohydrodynamic lubrication,the effects of the cavitation and fluid inertia on the sealing performance are investigated at high-speed conditions in spiral-grooved face seals.The mechanism of the cavitation and fluid inertia considering the thermal effect is revealed.A visual test rig for face seals is built and the cavitation experiments are conducted for the water-lubricated spiral-grooved face seal.The mechanism of cavitation and its effects on the fluid flow and tribological properties are investigated.The experimental results verify the cavitation suction effect and the reverse suction performance in the cavitation suctioning face seal.The research works in the dissertation provide theoretical bases and methods for the engineering design of the spiral-grooved face seals operating at high-speed conditions,enrich and expand the lubrication theories of spiral-grooved face seals,and the proposed models and numerical methods can also be used in the simulation analysis for the hydrodynamic bearings.