Flexible Seal Strip Design for Advanced Labyrinth Seals in Turbines

Abstract

The paper discusses the potential benefit of flexible seal strips in labyrinth seals for turbines. By reducing the radial stiffness compared to a standard straight and stiff knife, seal clearance could be reduced without significantly reducing the seal durability and long-term performance. As contact between the seal strips and the rotor can occur especially during transient operating phases, a more flexible design of the seal strips can prevent damage and wear, keeping the discharge rates constantly low. However, the pressure difference across the fin will cause a deflection of the seal strip due to the increased flexibility and thus creating an additional possible risk for an unwanted contact. Pressure balanced designs and supports on the low pressure side are used on the investigated seal designs to eliminate that risk. To give evidence of possible performance gain a standard labyrinth seal configuration is compared to two configurations with segmented and curved seal strips. In a first step, the discharge coefficient and the leakage rates for the nominal seal design are calculated using two-dimensional CFD. In order to investigate the impact of a worn seal tip on the leakage flow, the geometry change due to a rubbing event is simulated with FEA tools. Therefore, a specific high-speed wear model is implemented and calibrated by experimental data, enabling the correct cooling effects and plastic deformation. The discharge coefficient and the leakage mass flow rates of the worn geometry are then again modeled with CFD for the various seal configurations and compared to the unworn state. The study shows that a wise combination of the advantages of flexible curved seal strips can be used to reduce the leakage rates significantly, improving the life time of seal elements at the same time.

An Immersed Boundary–Lattice Boltzmann Approach to Study Deformation and Fluid–Structure Interaction of Hollow Sealing Strip

“…With the mechanical model of the material, it is convenient to simulate the sealing system by using the finite element method (FEM). The pre-compression deformation of the sealing strip [10] and the deformation and failure under the static fluid pressure difference [11,12] can be simulated accurately. The main defect of FEM to simulate the failure process of the sealing strip is that it only transforms the fluid action on a solid into a steady surface force, but does not simulate the flow and lead to a change of force after fluid movement.…”

Investigation of Hydrostatic Fluid Forces in Varying Clearance Turbomachinery Seals

“…This can be done by first considering isentropic conditions, using the smallest area and upstream and downstream pressure conditions as shown in Eq. (2) which is in the same form as presented by Herrmann [10].ṁ…”

Application of immersed boundary-lattice boltzmann method in failure of automobile door sealing strip

“…9 Later, some scholars carried out research on seal leakages, and proposed that the critical leakage pressure mainly depends on the geometric shape and constraint conditions of the seal. 10 In addition to the basic sealing function of automobile seals, it also affects the noise inside vehicles. The decrease in sound insulation performances of sealing strips is directly related to seal failure.…”