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ALL ú ú N01 Page 5 ú Feb 10/93
BOEING PROPRIETARY - Copyright (C) - Unpublished Work - See title page for details.
////////////////////////A / PW4000 SERIES /747-400 / ENGINES/MAINTENANCE MANUAL ////////////////////////
G. The case cooling manifolds of the high pressure turbine (HPT) surround the external turbine case and circulate fan discharge air to cool the surface of the case during cruise power operation. This cooling causes shrinkage of the case and decreased tip clearances between the blade tips and duct segments, resulting in improved turbine efficiency.
4. Low Pressure Turbine (LPT) (Fig. 3)
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A. The low pressure turbine (LPT) is attached to the external rear flange of the HPT case and provides the rotational driving force for the low pressure compressor (LPC) by extracting energy from the hot combustion gases and transforming the energy into motional energy or work. This energy drives the LPC through a turbine shaft, which runs through the center of the engine.
B. The LPT consists of four rotor stages and four stator vane stages. Cooling air is supplied to the case wall at the forward inner diameter, disk rim and blade root areas, and the inner rotor cavity areas. The LPT case is also cooled by the case cooling manifolds to improve cruise operating efficiency. A removable plug, located at the 4:30 o'clock position, provides access for borescope inspection of the 2nd-stage HPT and the 3rd-stage LPT.
C. The rotors of the low pressure turbine are a cantilevered rotor design, with the hub of the 5th-stage rear turbine as the primary rotating structural member. The 5th-stage hub provides a bolted attachment provision for the LPC driveshaft at the inner diameter and for the 4th-and 6th-stage LPT disks near the outer diameter. The 4th-stage disk mounts forward of the 5th-stage hub with a bolted attachment to the 3rd-stage disk. The 6th-stage turbine rotor is cantilevered to the rear of the 5th-stage hub.
D. Rotating knife-edge airseals are located between the 3rd- and 4th-stage, and 4th- and 5th-stage turbine rotors. These airseals are secured by the adjacent turbine disks. The airseal knife-edges along with integral knife-edges on the 6th-stage disk, align with an abradable honeycomb vane inner seal land to form the vane inner seal, which prevents gaspath leakage around the inner diameter of the vanes.
E. The 3rd-stage rotor blades are coated with an aluminized material, while the remaining stages are uncoated. Outer shrouds of the turbine blades incorporate interlocking hardfaced notches and double knife-edges seals, except for 6th-stage blades which have a single knife-edge seal. These knife-edges align with the abradable honeycomb (outer) airsealing ring segment installed in the turbine case.
5. Turbine Exhaust Case (Fig. 4)
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