The described subject matter relates generally to gas turbine engines and more particularly, to seal assemblies in gas turbine engines.
Seals such as labyrinth seals and brush seals are commonly used in gas turbine engines and other assemblies to restrict the escape of a working medium (e.g. air) from the main flowpath through a gap between a stationary part and a rotating part. Labyrinth seals are typically comprised of a series of knife edge features that can either contact an abradable surface or act as a non-contacting seal by providing a close tolerance gap to an adjacent journal.
In one specific application, labyrinth seals are used to separate the oil wetted environment of a bearing compartment from the surrounding air filled cavities and prevent oil from weeping out. Additionally, labyrinth seals are used to minimize the entry of air from entering the bearing compartment in amounts greater than the bearing and lubrication system of the gas turbine engine can handle. To achieve this function, labyrinth seals create a meandering pathway to help prevent undesirable amounts of leakage of oil out of or flow of air into the bearing compartment.
Although generally very useful, labyrinth seals typically allow for greater leakage than other forms of compartmental sealing like carbon seals. Thus, the use of labyrinth seals is constrained to certain portions of the engine where extra leakage will not compromise performance, engine functionality, or customer requirements. Additionally, labyrinth seals can experience problems at ground idle conditions where the delta pressure developed across the labyrinth seal becomes too low. In such scenarios, the propensity for oil to escape the bearing compartment increases. Depending on the location of the labyrinth seal in relation to bleed air directed from the gas turbine engine to passengers, this oil weepage can cause passenger discomfort at the smell of oil.