Abradable stator gas turbine labyrinth seals

Abstract

This is a detailed study into the internal aerodynamics of labyrinth seals, with pmic| reference to the effects of abradable honeycomb stators on labyrinth seal leakage.- A extensive experimental programme established tables of friction factor for three different grades of honeycomb used by industry, and examined the effect of both Reynolds number and clearance on these friction factors. The friction factor associated with a aerodynamically smooth surface was also experimentally determined in order to establish the experimental method. The experimental data was used to model the different grades of honeycomb used as stator material in numerical simulations of a number labyrinth seals, and allowed for comparison of the leakage associated with both smooth and abradable stator straight through labyrinth seals. Step-up and step-down seal geometries were also considered, and the effects of pressure ratio, clearance and rotation on labyrinth seal leakage was examined on all modelled seal types. This numerically generated leakage data was comprehensive enough to allow for the creation of a second-generation one-dimensional labyrinth seal leakage predictor tool of the type used by design engineers in network models. This tool accounts for stator material, seal clearance, overall pressure ratio, rotation and seal geometry, and the accuracy associated with this tool allows labyrinth seal leakage to b predicted to within 10%. Functions of discharge coefficient and carry-over factor obtained from the numerical predictions are used by this tool, and as such it is capable of dealing with a large number of different operating conditions for all the seal types modelled.