Study On Leakage And Rotor Dynamics Characteristics Of Annular Seals Of Centrifugal Pump

Centrifugal pumps are key devices in the national industry,such as petroleum,coal,chemicals engineering and power.They are also the core of the entire liquid delivery system.In recent years,high-power centrifugal pumps with high pressure,high speed and heavy load have been extensively used.The annular liquid seals in these centrifugal pumps,such as impeller seals,interstage seals and balance drums have important influence on hydraulic performance,head of delivery and efficiency,and vibration performance.In this paper,major content of the centrifugal pump seals consisted of the following three aspects.Firstly,Lattice Boltzmann Method(LBM)was used to calculate the leakage of smooth seals.Secondly,dynamic characteristics of the rotor and trajectory of the axis were researched by nonlinear method.Thirdly,the rotor-seal-bearing system test device was built and the results of test were compared with the predictions.Specific analysis as follow:(1)Two-dimensional LBM-LES numerical method was established to investigate the static characteristic and leakage of liquid seals.The numerical method consisted of incompressible fluid velocity model of D2G9,the LBM-LES turbulence model and unbalanced extrapolation format boundary conditions.In order to avoid the compressibility error in the numerical process,the pressure was used as dynamic variable.Three seals with different structures were verified by this method and the leakage were compared with results from experiments,business software which based on finite volume method and theory which based on empirical coefficients.The validity and accuracy of LBM in calculating the leakage of seals were proved.The lattice reference pressure calculation equation was modified based on Bernoulli equation of incompressible fluid.(2)The nonlinear motion model of centrifugal pump rotor-seal-bearing system was established.Base on Muszynska nonlinear seal water film force model and the nonlinear bearing oil film force model,the nonlinear equations were built and solved by and the fourth-order RungeKutta method.A single-axis single-stage seal rotor coupling system was simulated by the motion model.The vibration responses of different operating conditions and different rotor structures were analyzed.The rotor orbits,Poincare maps and bifurcation diagram were obtained under different characteristic parameters.By comparing the calculation results under different conditions,it was found that the greatest influence on rotor vibration was rotation speed,followed by seal clearance,seal length,sliding bearing lubrication length,seal radius,and pressure difference.(3)According to the dynamic stiffness principle of the seal liquid film,a rotor-seal test bed was designed and built.Commercial CAE software was used to check the test bed and determine the range of the test measuring of transducers.The function of the test bed included measuring the leakage of seals,drawing the rotor axis orbit map and measuring dynamic characteristic parameters of seals.In practical operation,leakage was measured by electromagnetic flowmeter,and rotor axis orbit map was drawn by two pairs of non-contact displacement sensors which were arranged orthogonally.After the measurement,the vibration signals were collected and filtered to obtain the rotor orbits under different operation conditions.Finally,the test data were analyzed to research the vibration law of the rotor.The results showed that due to the influence of Lomakin effect,the seals force at the clearance of the seals will produce restoring force on the rotor,which will reduce the amplitude of the rotor.In addition,the stronger the restoring force will be increased with the increasing pressure difference.