Brushes as High Performance Gas Turbine Seals

Abstract

Brush seals are the first simple and practical alternative, to the finned labyrinth, for gas turbine air system seals. Their use has been made possible by a combination of innovative design features, combined with advanced materials and manufacturing techniques. Due to the very high rubbing speeds and temperatures, existing in gas turbine air system seal positions, finned labyrinths have been used almost exclusively since the invention of the gas turbine. Development over the years has reduced their leakage flow to the ultimate, but leakage is very much dependent on clearance. A brush seal, replacing the best possible finned labyrinth seal, needing a clearance of 0.7mm, can reduce the flow to approximately 10% of that of the finned seal. The main advantages of brush seals, therefore, are their dramatic improvement in sealing performance. This is combined, however, with their ability to maintain this performance even during and after transient differential movements. These advantages have been developed and demonstrated after many hours rig and engine running. Back to back engine tests, with brush seals, replacing finned labyrinths in key air system seals, have demonstrated a significant improvement in thrust for a given stator outlet temperature (SOT). Flight trials are in progress, on an engine fitted with brush seals, as a further step to their in service use.