NASA NTRS1991
About four years ago, work was completed on a 36 inch diameter gas to gas carbon ring seal used to buffer low pressure turbine air at the rim of the forward outer flowpath on the GE36 unducted fan (UDF) engine. At about the same time, we were developing a long life counter-rotating intershaft air-oil seal of approximately 7.6 inch diameter for operation at 800 fps, 800 F, and 50 psid. Although we were successful in meeting most program goals with a split ring seal of the axial bushing type, the seal with the greatest payoff in life and air leakage rates, bearing many features in common with the GE36 seal, could not be successfully tested because of the structural weakness of the primary seal ring carbon material. This was a split ring seal using a hybrid combination of orifice compensated hydrostatic and shrouded hydrodynamic gas bearings. We are presently working to develop this design in conjunction with high strength materials being developed by Pure Carbon Co. In the area of engine secondary gas flow path-sealing for performance improvement, we are currently working with carbon and all metal face seals. A 15 inch diameter all metal 'aspirating' face seal, using self-acting hydrostatic bearings, was successfully tested to 700 fps, 100 psid, and 1000 F, demonstrating long life at flow reduction of 86 percent compared to a 'best' labyrinth. This seal will be developed through 1400 F, 900 fps, and 350 psid. The seal 'aspirates' closed at about idle speed pressure during engine start and reopens at engine shutdown. A hydraulic thrust balance seal, currently using orifice compensated hydrostatics, is under development. Other aspects of these projects are briefly covered.