Theoretical And Experimental Studies Of Dynamic Performance Of Spiral Groove Dry Gas Seals At High Speeds

Dry gas seals（DGSs）are widely used in shaft end seals of medium-high speed rotary machineries which used in petroleum and petrochemical industry,energy and electric power industry.But with these rotary machineries are more and more used in high-speed and high-pressure conditions,and the DGSs are spreading to coal chemistry industry and supercritical CO₂ Brayton cycle,the use cases of DGSs are not so good.Especially with the further increase of speed,it is influenced by excessive vibration of shaft and inevitable installation misalignment of seal rings and bad ability of anti-disturbance,failures are easier to be taken placed in DGSs because of the seal rings contact or crash.Hence,the researches and developments of high-speed DGSs with superior dynamic performance,which to be formed a suit of theories and methods of optimized design,will have a great significance not only for improving dynamic stability and usefull life of high-speed DGSs but also for ensuring high reliability and security of the key equipments of important field.The perturbation film pressure governing equations under three degree of freedom of DGSs are presented by perturbation method based on gas lubrication and dynamics theories,and they are solved by the method of finite difference.After validating the calculation procedure,the influence of working condition parameters and outside excitation conditions on dynamic characteristics coefficients of a spiral groove dry gas seals（S-DGS）have been analysed in the condition of high-speed and high-pressure.Furthermore,the influence of structure parameters of spiral groove on the dynamic characteristics coefficients also have been researched at a high-speed,but in different pressure conditions.It initially reveals the influence factors and change rules of dynamic characteristics of gas film,and builds a foundation for further studies about dynamic performance of S-DGSs.Axial and angular motion equations of a flexibly mounted stator of S-DGS are presented based on kinematics theory when the rotor’s axial vibration and angular misalignment are taken into consideration.And the transient-state variation rules of gas film thickness disturbance distribution and the maximum absolute value of the gas film thickness disturbance distribution are easy to be obtained after solving the motion equations.On this basis the transient-state Reynolds equation can be solved,and then the transient-state change rules of open force and leakage rate have been analysed.What’s more,the influence of working condition parameters and outside excitation conditions on dynamic tracking property and transient-state sealing performance have been thoroughly studied.And the transient-state working mechanism of the S-DGS is revealed by it.Considering the structure of DGS mechanical system have very important influence on dymanic performance,so the impacts of inside factors of DGS mechanical system such as spring stiffness,secondary seal damping,density and feature sizes of flexibly mounted stator on dynamic tracking property have been taken as the key research contents.Meanwhile,considering there are three common flexibly mounted ways of seal rings in DGSs,the theoretical models of the three kinds of DGS structures are built on a comparable approach.Ultimately,the results of gas film thickness disturbance of the three kinds of DGSs are comparing analysed,and it makes us to systematic understand their dynamic performance differences and the corresponding optimized design methods.It tends to conduct optimization study of DGS after taking good knowledge of its dynamic operation mechanism and performance evolution law.At that point,four kinds of gas film vibration forms and the corresponding occurrence conditions,which based on a large number of calculations,have been summarized.And on this basis,saltation peak and period peak of gas film thickness disturbance are defined as characterization parameters and optimization objective function of dynamic tracking property of DGSs.Based on variable-controlling approach and the method of full factorial design respectively,the optimization ranges and the interactions of structure parameters of spiral groove and characteristics parameters of mechanical elements have been researched under a certain optimization principles.At the same time,this paper,which bases on the good coverage property of hyperelliptic curve,puts forward hyperelliptic curve groove dry gas seals（HC-DGSs）.Under the same structure parameters with spiral groove,HC-DGSs have remarkable performance improvements compared with S-DGSs according to optimize the molded lines of hyperelliptic curve grooves.The theoretical researches can hardly do without experimental verification.Meanwhile,experimental study of dynamic behavior of DGS has been a major focus in order to satisfy the needs of engineering design.So a dynamic performance experiment rig has been set up,and experimental studies on transient-state opening process of S-DGS with flexibly mounted stator under different film thickness have been carried out.Furthermore,the influences of groove depth,spring stiffness and stator mass on gas film thickness disturbance and leakage rate have been experimentally studied,and the results of experimental study also have been compared with the conclusions by theoretical research.Results show that the theoretical results coincide well with the experimental data.In a word,the related theoretical and experimental research achievements of dynamic performance of high-speed DGSs have already formed a suit of optimized design theory and guidelines.