Calculation And Analysis Of The Dynamic Characteristics In The Large Steam Turbine Labyrinth Seal

With the constant increasing of the load and parameters of large steam turbines, the air vibration problems in the sealing system which can be characterized by cross-coupled stiffness and direct damping are becoming more and more serious. In this paper, the author focused on labyrinth seals of different kinds of configurations, and modeled, generated mesh, and made numerical calculation on them by using commercial software including SolidWorks, ICEM, and CFX in order to obtain cross-coupled stiffness and direct damping of seals. As a result, the author explored the factors affecting the seal and stable performance of sealing system.The research objects are mainly shaft seal, diaphragm seal, and shroud band seal.In order to obtain the nature of cross-coupled stiffness of sealing system with high rotor speed, the paper first simulates the sealing structures used in the experiments including the Childs' see-through labyrinth seal and its staggered modification as well as Pugachev's staggered labyrinth seal. With the increase of rotor speed, cross-coupled stiffness of different sealing systems in various prewhirl conditions decreases gradually. With normal rotor speed, the absolute value of the seal's cross-coupled stiffness with 0 prewhirl is close to 0. The stability of the sealing system is relatively high. Thus the paper verifies that with zero prewhirl control, shaft seal, diaphragm seal, and shroud band seal can be more stable. In addition, the shaft seal can provide negative cross-coupled stiffness to balance the overall rotor system and improve the stability as well. Then, the paper finds that with 0 prewhirl, the shroud band seal with back slope has lower absolute value of cross-coupled stiffness and higher direct damping, which means a higher stability of the sealing system. In order to verify this, the paper makes a corresponding discussion on the Pugachev's staggered labyrinth seal to prove that with different pressure ratio, density, and rotor speed, the back slope structure can increase the seal's direct stiffness. Thus, with zero prewhirl control, this structure can improve the stability of sealing system.To sum up, the paper mainly calculates and analyzes two sealing structures used in experiments as well as the actual turbine shaft seal, diaphragm seal, and shroud band seal, and improves the stability of the actual turbine labyrinth seals.