Research On Dynamic Characteristics Of Rotor System Considering Floating Ring Seal

Ring seal is an important component of rotating machinery.As a kind of contactless ring seal,the floating ring seal is widely used in all kinds of rotating machinery because of its simple structure,reliable operation and good sealing performance.Complex structure and harsh operating conditions make rotating machinery easy to get into abnormality in operation.In this complex flow field environment,a kind of interaction force is inevitably produced between floating ring seal and fluid,called fluid-structure interaction force.It can not only affect the performance of the floating ring seal but also seriously influence the dynamic performance of the whole rotor system.In the present paper,steady-state and dynamic fluid flow analyses are carried out for a type of floating ring seal that has important applications in engineering and the dynamic characteristics of a rotor system with the floating ring seal are studied,based on related theories of fluid dynamics and solid mechanics.Some relevant conclusions are drawn.Based on the Bulk-flow model,the nonlinear governing equations of flow field in floating ring seal clearance are established.The zeroth and first order dimensionless equations of the flow field in the clearance are obtained by nondimensionalization and perturbation analysis.An iterative method for solving the self-locking position of floating ring is developed by forces analysis according to the motion mechanism of floating ring seal.The finite difference method and the SIMPLE algorithm are applied to the discretization and solution of the dimensionless governing equations.A MATLAB computer program is written to complement the numerical calculations.Firstly,the steady-state pressure and velocity distributions of the flow field in floating ring clearance are numerically calculated and analyzed.Results show that the axial velocity of steady-state flow field does not change along the axial direction and increases along the circumferential direction with the increase of the clearance thickness.The circumferential velocity increases rapidly near the clearance inlet,then gradually becomes gentle along the axial direction,and decreasesalong the circumferential direction with the increase of the clearance thickness.The pressure decreases linearly from clearance inlet to outlet along axial direction and decreases along the circumferential direction with the increase of the clearance thickness.Considering the structure and operating condition of the floating ring,the influences of related parameters on the steady-state and dynamic performance of the floating ring are analyzed.Results show that the leakage of the floating ring decreases with the increase of fluid viscosity,floating ring length and rotor speed,increases with the increase of floating ring thickness,and increases first and then decreases with the increase of inlet swirl coefficient.The self-locking eccentricity of the floating ring decreases with the increase of fluid viscosity,inlet swirl coefficient,floating ring length and rotor speed,and increases with the increase of floating ring thickness.The angle between locking eccentricity and initial eccentricity always increases with the increase of the parameters.The bearing capacity of the fluid in floating ring clearance to the rotor increases with the increase of floating ring length,floating ring thickness and rotor speed,decreases with the increase of fluid viscosity,and increases first and then weakens with the increase of inlet swirl coefficient.The differential motion equations of a Jeffcott rotor system with floating ring are established in four degrees of freedom by using finite element method and dynamic characteristics of the system are analyzed according to numerical calculation results.The results show that the free whirling orbits of the rotor are elliptical.The natural vibration modes of the rotors vary wildly with the orders of critical speed,and the higher the orders of critical speed are,the more complex the natural vibration modes of the rotors are.Finally,the influences of structural and operational parameters of the floating ring on the first five order critical speeds and stability of the system are analyzed.The results show that each parameter has a great influence on the first three order critical speeds of the system.In detail,each order critical speed decreases with the increase of fluid viscosity,and increases with the increase of inlet swirl coefficient,floating ring length and thickness.At low speeds,the system stability decreases with the increase of fluid viscosity,inlet swirl coefficient and floating ring thickness,and increases with the increase of floating ring length.When the speed increases up to acertain value,the system stability increases with the increase of fluid viscosity.