Nonlinear Dynamic Stability Analysis And Response Optimization In The System Of Dry Gas Seal

Dry gas seal is a new type of non-contact mechanical seal，it is the latest technologyapplication results of modern fluid dynamic pressure lubrication theory in the Sealingtechnology. Because of gaseous film gap is only3~5μm，it is easily affected by outsideinterference and structural parameters，Most likely lead to dry friction between the sealring or increased leakage，So it is the key of gas seal to keep the dynamic stability of gasfilm and seal rings. The stability of the gas seal is closely related to its dynamics，dynamics characteristics has been the study of technical difficulties at home and abroad.Dry gas seal system itself is a nonlinear system，dynamics characteristics should benonlinear，the paper takes spiral groove dry gas seal as research project，nonlineardynamic stability of gas film lubrication has been studied. Nonlinear dynamic behavior ofgas has been studied from both axial and angular，the aim is to seek the stability range ofsealing spiral angle，it has important theoretical significance in dry gas seal design andoptimization.Based on the N-S equation and slip boundary condition，a nonlinear Reynoldsequation for a steady-state and micro-scale flow field was derived.Using PHlinearization，the nonlinear partial differential equation can be transformed into the linearpartial differential equation，and then using complex function it can be transformed intotwo linear differential equation again.The problem was solved by using small parameteriterative method，and the approximate function expression of gas dynamic pressure in thespiral groove was obtained，and then the solution of flow velocity and spillage were foundout，the film reaction increment of axial perturbation has been obtained，and then usingcomplex function and iterative method to solved static gas film boundary value problem，the approximate function expression of gas film stiffness and damping was obtained，andthrough the analysis of the prototype， the law of stiffness and damping with the variationof pressure and speed was obtained，it could be provide a basis for optimizing the design.Dynamical model on a system of gas film and static seal ring subjected to axialvibration was established，and the axial vibration equation was solved by using theprogramme，then the vibration phase chart，the Poincare’ mapping chart and the time history chart responded by structural parameter of the spiral groove were obtained，andaxial nonlinear dynamic behavior on spiral grooved gas seal system was discussed. Thecorrectness of the model was verified by the special case，and then the chaos can becontrolled by selecting reasonable structure parameters of the spiral groove. Acomputation model on the fluid-solid coupling system of gas film and seal rings subjectedto axial vibration was established by taking static seal ring as the oscillator，the vibrationequation was solved by using the Runge—Kutta algorithm，then the vibration phase chartand the time history chan responded by the different spiral angles and grooved depth wereobtained，and the effect of spiral angles and grooved depth on vibration displacement wasanalysed. The optimal value was obtained by example which are in agreement with theexperimental data，which provides the theoretical basis on dynamical optimization designof gas seals.The dynamic model of the angular wobbly of the gas film and seal ring wasestablished，and the gas film angular rigidity，critical moment of inertia and thetwo-dimensional angular wobbly vibration equation were solved by using the perturbationmethod and the Runge-Kutta method，then the seal structure stability and instabilityparameters were obtained，and the vibratory response of best stability point and criticalpoint were analyzed. The vibratory response of best stability point is quasi-periodicmotion，but response of critical point is chaotic motion. The program can be used toanalysis on angular wobbly，and then to obtain stable range of the spiral angles，whichprovides the theoretical guidance on optimization design of dry gas seals.The experimental investigation of dry gas seal prototype was conducted on the3000r/min sealing test device in ChengDu YiTong Seal Co.，Ltd. The research finishedoverall plan of instrumentation system and hardware configuration，tested leakage，powerlose，gaseous film rigidity and sealing ring axial vibration displacement，obtained testresults and analyzed error between test and calculation data. Comparing some data fromexperiments with that of approximate calculation，the results show that dynamical andmathematical model on a system of gas film and seal ring of the spiral groove dry gas sealis validated correctly，and the developed program of approximate analysis method ispracticable.