Study Of Flow Characteristic And Efficiency Improvement Technology For Turbine Seal

With the development of turbine with large capacity and high parameters,seal becomes more and more important because its performance is related with the efficiency and safety of turbine.Designing high-performance seal is one of the difficulties which must be solved in the development of large turbine.So mastering work mechanism and studying new-style seal are of great theoretical significance and engineering value.This paper conducted researches on shaft end seal and blade tip seal simultaneously.In this paper,the three-dimensional CFD model of labyrinth seal was established to study flow characteristic.Results showed that labyrinth seal can seal fluid relying on throttling effect occurred at tip clearances and energy dissipation occurred at cavities.The leakage increases with the increased pressure ratio and seal clearance.The non-uniform circumferential pressure distribution caused by the spiral flow will result in flow induced force.Crossed-coupled stiffness increases with the increased pressure ratio and preswirl velocity.Additionally,low-frequency whirl is easy to be found in labyrinth seal.At the basis of staggered labyrinth seal,the mixed labyrinth seal was proposed and the comparisons between staggered labyrinth seal and mixed labyrinth seal were then done.Results showed that the leakage of mixed labyrinth seal is 30%lower than that of staggered labyrinth seal.Mixed labyrinth seal has a smaller cross-coupled stiffness than staggered labyrinth seal.By the analysis of structural parameters,it can be found that mixed labyrinth seal has an optimal lateral teeth height and the lateral teeth gap should be as small as possible.In order to avoid the rub between two lateral teeth,the lateral teeth gap should be set bigger than the vertical clearance.In order to make a better understanding of flow characteristic within blade tip seal,a one-control-volume model with stratified flow was set up,which combines blade tip seal and rotor blade.This new model can predict the existence of underturned flow accurately.In order to study the influence of structural parameters on leakage,the one-control-volume model with mixed flow and two-control-volume model with mixed flow were put forward.The maximum error of leakage among above three models is 7.1%.Using the two-control-volume model with mixed flow to make structural analysis,it can be found that the leakage increases with the increased seal clearance and the influence of seal cavity depth and width on leakage can be ignored.The gas film compound seal was put forward in this paper,calculation and comparison were made to study the performance of the new seal.Results showed that the pressure drop mainly occurs at gas film seal while the throttling effect of labyrinth seal is not obvious.Compared with labyrinth seal,gas film compound seal has a better performance.The leakage of gas film compound seal is 0.75%of labyrinth seal,the efficiency increases from 91.52%to 93.73%.For gas film compound seal,the leakage increases and efficiency decreases with the increased gas film thickness.