Vibration Stability And Unbalance Response Analysis Of Floating Ring Gas Film Seal

In view of the requirements of high-parameter operating conditions of aviation gas turbines,it is extremely important to select an effective sealing method to cope with the sealing requirements under extreme operating conditions of the system.The floating ring gas film seal is a sealing method that can achieve non-contact operation while achieving efficient sealing.It can meet the sealing requirements of a series of rotating machinery,including aviation gas turbines,and plays a key role in improving the stability of rotating machinery and reducing system energy consumption.However,there are few research on the stability of the floating ring gas film seal system,and the stability of the seal system is one of the key factors that determine whether the whole rotating machinery can work normally.Therefore,it is very important to study the stability of the floating ring gas film seal.Firstly,the dynamic Reynolds differential equation with trace disturbance is solved,and the dynamic characteristic parameters under sealing film forming are obtained.The self-vibration control equation of gas film-floating ring is established by using small disturbance linearization distribution parameters.The Routh-Hurwitz criterion is used to judge the stability of the system,and the quadratic regression model is used to study the influence of simultaneous changes of two parameters on the stability of the rotor system under different working conditions.The results show that the average gas film thickness is the largest,the eccentricity and the number of grooves are the second,and the spiral groove length is the smallest among the factors affecting the natural vibration stability of the floating ring.The optimal structural parameters of the system are as follows : the average gas film thickness is 8.74μm,the number of slots is20,the slot length is 10.15 mm and the eccentricity is 0.3.Under this structural parameter,the actual stability margin reaches 3.6715,and the error with the theoretical maximum value of 4.2871 is 14.4 %.Secondly,due to the effect of fluid excitation force,the sealing system will induce large transverse vibration of the sealing rotor,which will affect the stability of the system.Therefore,this paper uses the Jeffcott rotor model and introduces the Muszynska sealing force model to describe the motion state of the fluid in the sealing gap.The dynamic models of the sealing rotor system with and without mass eccentricity are established respectively.The Newmark-β method is used to solve the system dynamics equation,and the bifurcation diagram,Poincare diagram and time domain response image of the system under different rotational speeds are drawn.The results show that considering the mass eccentricity can improve the stability of the sealed rotor system,and the stable speed of the system is the largest when the dimensionless mass eccentricity is about 0.3.The maximum stable speed of the system decreases with the increase of pressure difference.The increasing rotational speed will cause the instability of the periodic solution of the system,and the quasi-periodic motion,sub-harmonic motion and chaotic motion appear,and the dynamic behavior of the system becomes very complex.Finally,a floating ring gas film seal test rig was built,and the vibration sensor and acoustic emission detection device were used to collect the data of the system operating state under different working conditions.The identification of the system operating state was realized by analyzing the vibration sensor and acoustic emission data.The results show that when the rotational speed is about 24000 r/min,the characteristic frequency of rubbing appears in the acceleration spectrum of the system,and there is a certain degree of clipping phenomenon in the time domain waveform.The characteristic frequency of seal rubbing appears in the acoustic emission energy spectrum,and the root mean square value also changes abruptly.The leakage rate of the floating ring gas film sealing system increases correspondingly,and the stability of the gas film sealing system is insufficient.