Dynamic Characteristics And Surface Morphology Analysis Of Compliant Foil Gas Seal

Noncontact cylindrical gas film seal technology is the core technology of highquality rotating machinery.This technology can be applied to extreme parameters with noncontact surface.The sealing system composed of cylindrical gas film seal has a vital influence on the stability,low energy consumption ratio and reliability of the system.At present,there are few research on the compliant structure forms of cylindrical gas film seal.Compliant foil gas seal can reduce the friction and wear of sealing interface and prolong the sealing life as one of the structural forms of cylindrical gas film seal.It has important value for improving the dynamic characteristics of high-quality rotating equipment.In this dissertation,the seal characteristics of compliant foil gas seal are analyzed on the basis of compliant foil deformation,including steady-state characteristics,dynamic characteristic coefficients and dynamic characteristics.The variation trends of these characteristics are analyzed with variation of different operation conditions and structural parameters.Futhermore,the accuracy of the numerical analysis method is verified by the experiments of gas seal under different surface conditions.The major research of this dissertation can be divided to three parts:Firstly,the structural advantages of compliant foil gas seal is analyzed according to compliant foil deformation in this dissertation.On the basis of the structural advantage,the new variable angle spiral groove is designed in this dissertation.The steady state of variable angle spiral groove on leakage,gas force and friction moments are obtained with the variation of speed,pressure,gas film thickness and eccentricity.As the same time,the variation trends of variable anagle spiral groove on steady characteristics is compared with traditional spiral groove,stepped groove and T-groove.Compared with the other different groove structures of seal interface,it has lowest leakage rate and largest gas film force.The results show that the variable angle spiral groove has lower leakage rate,larger gas film reaction force and the ratio of leakage to gas force than that of other groove type.Therefore,the variable angle spiral groove in the compliant foil gas seal has an advantage over other groove types.Secondly,the coupled structure of compliant foil gas seal is still analyzed and the transient Reynolds equation is solved on the basis of compliant foil deformation in this dissertation.The variation trends of the dynamic characteristic coefficient of compliant foil gas seal are acquired with eccentricity,film thickness parameters,speed and differential pressure.As the dynamic characteristics of compliant foil gas seal affected by dynamic characteristic coefficients,the dynamic characteristic of compliant foil gas seal-rotor system is analysed and solved by applying the Newmark method.With variation of speed,eccentricity and mass imbalance,the disturbance track and amplitude response of rotor center for compliant foil gas seal are obtained.The results show that the effect of eccentricity is more clear on the stability of gas seal rotor system.Finally,the test rig of gas seal is built to vertify the accuracy of numerical analysis.The sealing characteristics of the gas sealing system change with the variation of surface topography.The experimental results vertify the accuracy of steady state analysis.Furthermore,the experiment shows that the sealing hysteresis and anti-hysteresis phenomenon of compliant foil gas seal occur with the surface topography varying.The anti-hysteresis phenomenon shows that the leakage of acceleration period is lower than that of the deceleration period.This phenomenon is caused by the elastic elements of the compliant foil,system friction and the variation of operation conditions.As the same time,the acoustic emission frequency of different surface topography are obtained.The acoustic emission frequency is mainly by the strcucure of gas film.The effects of differential pressure on the acoustic emission frequency are ignored.Therefore,the acoustic emission technology can be applied to monitor the surface topography of seal interface.These acoustic emission frequency provides a scientific theory for the application of acoustic emission technology in the field of gas film seal.The experiment shows that the seal performance of gas film seal and the reliability of numerical analysis clearly descrease with the surface roughness higher than Ra0.8.The experimental leakage is also obviously rise.As the same time,the sealing hysteresis and anti-hysteresis phenomenon is obvious.Futhermore,acoustic emission frequency of cylindrical gas film seal shows at least two acoustic emission frequency characteristics.This is caused by the clearance variation of wedge structure.Through the analysis of the dynamic characteristics and surface topography of compliant foil gas seal,this dissertation provides a theoretical and engineering basis for the further coupled research of compliant structure and the flow pattern of compliant foil gas seal.This is helpful to realize the quantitative design of cylindrical gas film technology such as compliant foil gas seal as soon as possible.