Advanced Labyrinth Seals for Steam Turbine Generators

Abstract

A new class of knives (C-Shaped) for reduced labyrinth seal discharge has been designed and assessed through two dimensional numerical modeling of the seal’s internal flow passages. Modeling procedures used for the analysis have been previously validated by comparison with static labyrinth seal experiments. The objectives of the new seal are to: 1) reduce flow leakage through the seal and 2) introduce structural flexibility in the knives so that design clearances could be maintained even after rub events during startup. The baseline chosen for comparative evaluation is an N2 packing used in GE steam turbines. The new seals have compliant C-shaped knives instead of the straight knives, found in an N2 packing. The best performing configuration has one tall ‘C’ shaped long knife and three ‘C’ shaped short knives in each stage. It was found that the best configuration at clearances similar to the baseline seal reduces flow leakage by 42%. Two dimensional numerical structural analyses showed that the new seal knife is more flexible than a straight knife. This is also intuitive by virtue of its geometric profile. A non-dimensional geometric parameter correlates with the degree of flexibility in the knife. These results indicate a potential for design of labyrinth seals that maintain lower design clearances throughout their life time by carefully selecting the knives’ geometric parameters and incorporating high performance composite materials. Then, the new design would result in significantly lower steam leakage.

Experimental investigation of effect of tooth geometrical parameters to flow characteristics in slant labyrinth seals

“…Labyrinth seals are an important component of gas and steam turbine design, and the effective seals have shown high benefit-to-cost ratios as a result of their high performance payoff and their relatively low research and development costs. 3 Flow through a labyrinth seal can be considered as flow through a highly frictional path provided with a series of orifice type restrictions. In a sense, losses caused by individual restrictions combine to result in a reduced total pressure at the seal exit.…”

“…Labyrinth seals are an important component of gas and steam turbine design, and the effective seals have shown high benefit‐to‐cost ratios as a result of their high performance payoff and their relatively low research and development costs …”

Demonstration of a Dynamic Clearance Seal in a Rotating Test Facility

“…Many researchers have investigated geometric parameters of the labyrinth seal, such as fin pitch [8], tooth shape [9], cavity shape [10] and seal eccentricity [11] to name a few. The use of air curtains can also be utilised to improve the performance of labyrinth seals.…”

Labyrinth Seals - A Promising and Effective Design

“…Their characteristics were studies [31,32,33], and the obtained results show that a good configuration of a seal should be able to provide high rate of kinetic energy dissipation.…”