(3)
The turbine nozzle is formed by 17 vane clusters, with two vanes per cluster for a total of 34 vanes, secured to the 1st-stage HPT (blade) cooling air duct and inner combustion chamber. The vanes are air cooled by cooling air entering the internal passages of each vane and exiting through a specific pattern of holes to provide a protective film over the gaspath surface of the vane. The nozzles formed by the ring of vanes increase the velocity of the hot gases exiting the combustion chamber and direct these gases to provide the optimum angle, pressure, and flow to the 1st-stage turbine blades.
(4)
The 1st-stage HPT (blade) cooling duct directs cooling air from the inner combustion chamber area of the diffuser case through a metering nozzle and directs or impinges the air on the turbine rotor for cooling the 1st-stage HPT blades. The cooling duct case contour also forms the rear inner portion of the combustion chamber. Honeycomb seals are provided at the interfaces with the 1st-stage rotor to reduce leakage of the 1st-stage HPT blade cooling air.
C.
High Pressure Turbine (HPT) (Fig. 13)
(1)
The high pressure turbine (HPT) provides the rotational driving force for the high pressure compressor (HPC). The HPT is located at the rear of the diffuser and combustor and forward of the LPT. The HPT consists of two turbine rotor stages, a case and vane assembly, and a rotating inner airseal. These items are housed within the HPT case and are air cooled. The HPT case is cooled by the HPT case cooling manifolds.
(2)
The 1st-stage turbine rotor employs single crystal material blades, which are cooled by air from the diffuser. Cooling air to the 1st-stage turbine blades is metered by the cooling air duct in the turbine nozzle. The blades are internally air cooled and externally film cooled.
(3)
The 2nd-stage turbine rotor employs directionally fixed shroudless blades which are internally cooled from a mixture of the 12-stage compressor and diffuser air. Cooling air is reduced at cruise for increased performance.
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A
SEE A A
A
HUB (1ST-STAGE) TURBINE FRONT
KNIFE-EDGE SEALS HPT ROTATING 2ND-STAGE AIRSEAL HUB (2ND-STAGE) INTERMEDIATE TURBINE
CONFIGURATION THREE KNIFE-EDGE
HPT BLADE 1ST-STAGE BLADE 2ND-STAGE HPT
1ST-STAGE HPT TURBINE CASE DUCT SEGMENT 2ND-STAGE HPT DUCT SEGMENT
CLUSTER 2ND-STAGE VANE A-A 1193 L-A0524
Figure 13 High Pressure Turbine (HPT)
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(4)
The 2nd-stage HPT vanes are internally air cooled by 12th-stage compressor air through four externally routed tubes which mount to bosses on the turbine case. Two of these tubes contain valves which are closed to reduce cooling air flow at cruise conditions to improve performance. An inner air seal is located on the inner diameter of the 2nd-stage vane clusters and is part of the 2nd-stage vane inner seal. This seal is cooled by nozzles mounted on the inner diameter of the vanes.
(5)
The HPT case cooling manifolds 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.
D.
Low Pressure Turbine (LPT) (Fig. 14)
(1)
The low pressure turbine (LPT) provides the rotational driving force for the low pressure compressor. This rotational force is transmitted through a shaft at the engine core and coupled to the low pressure compressor. The operating speeds, pressures, and temperatures, are lower than that of the high pressure turbine as the combustion gases expand and energy is extracted.
(2)
The low pressure turbine is a four stage turbine mounted onto the rear of the high pressure turbine and is located forward of the turbine exhaust case. The 3rd- and 4th-stage turbine rotors are each cantilevered and attached to the forward side of the 5th-stage rear turbine hub. The 6th-stage turbine is attached to the 5th-stage rear hub and is cantilevered to the rearward side. Knife-edge seals are positioned between each of the rotating stages, near the inner diameter, to seal the stator vanes from gaspath leakage around the vanes.
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