| The seal problem is one of the main key factors that affect the development of modern turbine machinery to high power and stability.The self-adaptive gas film seal is a potential developmental seal with low-leakage and high performance,which is an important approach to promote the development of turbine machinery toward high performance.It is of great theoretical significance and engineering value to carry out the corresponding theoretical and experimental research on this seal.In this study,the basic research of self-adaptive gas film seals was first performed,and then based on the self-adaptive gas film seal,the technology of efficiency improvement and vibration reduction for turbine machinery seal was proposed.To begin with the one-dimensional theory,the fluid mechanism and governing model of the selfadaptive gas film seals were studied.The performance of efficiency improvement and vibration reduction for gas film seals was analyzed.The accuracies of Whipple's narrow groove theory and Muijderman's narrow groove theory were compared.The results show that,the flow of the gap fluid inside the gas film seals can be regarded as the Poiseuille flow caused by the drive of inlet and outlet pressure difference in the radial direction and the Couette flow caused by the relative velocity between rotating ring and static ring in the circumferential direction.The fluid leakage inhibition ability of gas film seals is better than that of traditional labyrinth seals.The fluid force is pointed to the axial direction,and the seal induced vibration problem does not exist.The Whipple theory underestimates the load-carrying capacity of gas film seals,and the leakage accuracy is greatly affected by the gas film thickness.The Muijderman theory takes into account the effect of medium compressibility and has higher precision.The differences in gas film force and leakage between the two models are about 16% and 14%,respectively.The solution process of Muijderman's equations is accompanied by the boundary initial problem and shooting method problem,which cause difficulties in the solution.An approximate solution to Muijderman's equations was proposed by using the Adomian decomposition method.The approximate solution is brief in form,and has low computational cost.The error is below 5%.On the basis,an explicit solution to Muijderman's equations was proposed by using the Cauchy integral theorem solution method.The explicit solution does not sacrifice the accuracy of the solution,and the gas film seal performance can be accurately obtained.Compared with the traditional solution method,the new solution methods are simpler and more convenient.They can be utilized to guide the design of gas film seals,and the engineering problem can be solved quickly.On the basis of one-dimensional theory,a two-dimensional numerical model of gas film seals was proposed,which can consider the effects of more complex factors on the gas film seal performance.By comparing with the three-dimensional CFD,it was found that the error between this model and the CFD was less than 4%,but the computational cost was small.Using this model,the accuracy of Muijderman's narrow groove theory and the effect of the groove shape on the gas film seal performance were studied.The results showed that the narrow groove theory over predicted the gas film force,leakage and gas film stiffness,especially the accuracy of the predicted gas film stiffness was poor,and the error was up to 52% in some cases.The load-carrying capacity,resisting disturbance ability,and power consumption of trapezoidal grooved seal were poorer than those of spiral grooved seal,while the sealing ability of trapezoidal grooved seal was better.The main difference was reflected by the decreasing stability in the trapezoidal grooved seal.In order to study the formation mechanism and influence factors of gas film,a hydrodynamic pressure test rig was built,and the measurements of gas film thickness,gas film resistance,and thrust disk speed can be achieved.The extinct experiment of the light-emitting diode indicated that a complete gas film was formed between the thrust disk and the pads,which separated the dynamic and static rings.The load-carrying capacity of the gas film,1.47 N,equaled the gravity of the thrust disk.The thrust disk can rotate continuously about 15 s.The maximum speed was 350 r/min,and the thickest gas film was around 5 ?m.The center region of the thrust disk bottom surface was higher than the marginal region,which reduced the effective area of the gas film and led to that the gas film gap in the measurement is smaller than that of the theoretical calculations.The three bumps on the thrust disk bottom surface intensively affected the gas film stability,which increased the chance of surface contact and led to the swing motion of the tilting pads.Improving the surface quality of the rotating ring(e.g.,reducing the irregularity of the rotating ring)is conductive to the formation of gas film,and the gas film stability is enhanced.According to the working environment of steam turbine,the effect of medium factor on the gas film seal performance was studied.Three superheated steam theoretical models including ideal gas method,corresponding-state-principle compressibility factor method,and IAPWS-IF97 method were compared.The results indicate that,the ideal gas method is simple and is suitable for the superheated steam with the compression factor approaching 1.The IAPWS-IF97 method is the most accurate,but the computational cost is high.The corresponding-state-principle compressibility factor method is between the two methods.The effect of the medium on the gas film performance is mainly reflected by the different viscosity.The viscosity of superheated steam is between air and methane.Therefore,the superheated steam slightly reduces the gas film performance compared to air,and slightly improves the gas film performance compared to methane.The relative difference between them is lower than 8%.The effect of the medium on the gas film seal performance is small.At last,a new type of steam turbine blade-tip compound seal based on the self-adaptive gas film seals was proposed.The aim was to reduce the turbine tip leakage loss and fluid induced vibration problems.Based on the self-adaptive gas film seals,a three-dimensional CFD model of steam turbine blade-tip leakage was built,and the leakage loss of the compound seal and its effect on the aerodynamic loss of the fluid inside cylinder were analyzed.The dynamic characteristics of the compound seal and the effect of the rotating ring deformation on the gas film gap were studied.The results showed that the compound seal had high fluid resistance,which reduced the tip leakage loss and the efficiency loss caused by the leakage.Compared with the traditional blade-tip two-tooth labyrinth seal,the leakage rate of the compound seal was reduced by 99.3%,and the efficiency of the rotor stage was improved by 1.9%.Increasing the seal ring area and spring stiffness can improve the tracking ability of stationary ring and enhance the stability of the gas film.Thickening the rotating ring can improve the strength of the rotating ring and reduce the effect of the structural deformation on the gas film gap.The introduction of the blade-tip gas film seal provides a new way to solve the problem of seal's efficiency improvement and vibration reduction and it is a potential approach to further improve the turbine machinery efficiency. |
PDF Full Text Request