The Numerical Analysis Of The Influence On Aerodynamic Performance By Large Steam Turbine Labyrinth Seal Structure

Because of the advantage of simple structure, low cost and convenient installation,labyrinth seals are widely used in steam turbine, gas turbine and other large impellermachineries. But in the process of actual operation, the rotor axis and stator axis are notcompletely overlapped, so there will be a flow vibration force which is circumferentialnon-uniform on rotor by the fluid in the seal. And study shows that the labyrinth seal isone of the main sources of flow vibration in steam turbine. So it is very important tostudy the dynamic characteristic of labyrinth seal and look for the sealing structure withgood stability.In this article, as an example, we establish a CFD calculation model of the straightlabyrinth seal and provide a numerical calculation with simulation software CFX. Thenmake a grid independence analysis to make sure the mesh density required by thecalculation precision. We also make3D modeling, steady and unsteady calculations onstraight, staggered and high-low tooth labyrinth seals separately to get their leakage, thedirect damping and the cross-coupled stiffness coefficients, and to observe the flow fielddistribution in those seals, the flow chart, the velocity vector and the circumferentialvelocity contours, and to compare their leakage features and stability. Then we analyzewhen the convex platforms and staggered structures are in different positions, thestability of high-low tooth and staggered tooth will be affected in some degree.Based on the results of the simulation as the above instruction, we carry on thenumerical simulation and analysis for the regulating stage of the1000MW thermalpower unit, which is in Suizhong power plant of Shenhua Guohua Electric PowerResearch Institute (Beijing).Then we observe the flow field, the velocity and streamlinedistribution inside the seal and calculate the leakage and dynamic characteristics of theseal. On this basis, we put forward the optimization design and improved scheme of thegoverning stage sealing, and analyze their respective leakage, the direct damping andthe cross-coupled stiffness coefficient, and identify the sealing structure form with thebest stability. In addition, we calculate the leakage, cross-coupled stiffness and the directdamping coefficient of the regulating stage seal under different seal clearance androtating speed to make sure the influence on the stability and the leakage of seal by the seal clearance and rotating speed.From what has been discussed above, this article not only analyzes the labyrinthleakage and dynamic characteristics of the three kinds structure forms of labyrinth seal,and also perfect the regulating stage seal in high pressure of the1000MW thermalpower unit which is in the engineering practice, to ensure its stability.