Investigating Material Removal Mechanisms in Aero-engine Turbine Fin Seals

Labyrinth seal systems are used in aero-engines to seal the clearance between turbine blades and the surrounding engine casing. An understanding of the material removal mechanism by which this occurs is necessary to achieve better sealing performance. In this work series of tests was conducted on a high-speed test rig capable of achieving fin tip speeds between 100 and 200m/s. The mechanism by which the fin removes material was investigated over a range of incursion rates, with force and temperature measurements along with high-speed imaging recorded in each case. Surface examination and sectioning was also performed using multiple post-test analyses includes microscopy, X-ray fluorescence, scanning electron microscopy as well as 3D surface scanning. The wear mechanism was found to be incursion rate and material dependent. For a certain material couple, abradable material is removed via a cyclic process at low incursion rates (0.02µm/pass), where it is first compacted in the worn groove, until ductility is lost and material fractures away from the surface of the groove. At high incursion rates (2µm/pass), material is extruded out of the sides of the groove forming lips, before fracturing off. This process is more efficient with lower relative forces and temperatures. As the incursion rate increases from low to high, the mechanism shows a gradual transition, with compaction being replaced with extrusion. The material properties like thermal conductivity and hardness also influence wear performance. Where harder and lower thermal conductive abradable results in worse fin wear while harder and low thermal conductive fin material protect the fin during the incursion period.