CORTE NACIONAL DE JUSTICIA, SALA DE LO CIVIL y MERCANTIL

In this section we will individually describe the GG assembly components and their functions.

These components are the FOD screen, bellmouth and bulletnose, compressor, combustor, HP turbine, and accessory drive.

Figure 2-21.—LM2500 GTE inlet (FOD screen, centerbody (bulletnose), and bellmouth).

FOD Screen

The FOD screen, or air inlet screen (fig. 2-21), is mounted on the module barrier wall. The purpose of this screen is to prevent foreign objects larger than 1/4 inch from entering the engine.

The screen will also prevent items from entering the engine if the blow-in doors open.

After major work, major intake cleaning, or anytime the ship is coming out of a shipyard environment, a special screen is used. It is a nylon screen that attaches over the metal FOD screen.

The nylon screen will catch particles much smaller than the metal screen will. You must be careful not to exceed specified throttle limitations when using the nylon screen. Exceeding throttle limitations could starve the engine for air and cause a compressor stall. NAVSEA issues specific instructions for use of the nylon FOD screen.

Bellmouth and Bulletnose

The bellmouth and bulletnose (centerbody) (see fig. 2-21) are mounted on the forward end of the compressor front frame. These components are used to direct air from the inlet plenum to the compressor. The surfaces of the two components have a smooth coat to reduce the turbulence of the airflow into the engine. The bellmouth also contains the water wash manifold. The water wash manifold is used to inject fresh water and/or a cleaning solution into the engine. This is done when the engine is being motored. This procedure is for maintenance purposes to clean deposits from the compressor. The water wash manifold is supplied by a common water wash system piped as a ship’s system.

Compressor Section

The LM2500 GTE compressor (fig. 2-22) is a 16-stage, HP ratio, axial-flow design. Major

Figure 2-22.—LM2500 GTE compressor components.

Figure 2-23.—Compressor front frame.

components are the compressor front frame, a compressor stator, a compressor rotor, and the compressor rear frame. The primary purpose of the compressor section is to compress air for combustion. A secondary purpose of the compressor section is to provide air for engine cooling, sump seal pressurization, and bleed air for ship’s service use.

Air is drawn in through the front frame. Then it passes through successive stages of compressor rotor blades and compressor stator vanes. The air is compressed as it passes from stage to stage.

After passing through 16 stages, the air has been compressed in the ratio of about 16 to 1. The

inlet guide vanes (IGVs) and first six stages of stator vanes are variable; their angular position is varied as a function of GG speed and compressor inlet temperature (CIT) by hydraulic fuel pressure from the main fuel control (MFC). This provides stall-free operation of the compressor throughout a wide range of speed and inlet temperature. Because these blades are able to be set at different angles, the term variable geometry applies to this compressor.

FRONT FRAME.—The compressor front frame (fig. 2-23) provides the forward attachment point for the GTE, supports the forward end of

Figure 2-24.—Compressor rotor.

the compressor section, and forms a flow path for compressor inlet air. Five struts (see strut positions, fig. 2-23) between the hub and the outer case provide passages for lube oil, scavenge oil, seal pressurization air, and a vent for the A-sump components. The bearings of the engine are numbered 3 through 7. The No. 3 bearing, which supports the forward end of the compressor rotor and the inlet gearbox, are located in the A sump.

The compressor inlet total pressure (P_t2) probe and CIT sensor (not shown) are mounted in the outer case. The No. 3 strut (6 o’clock position) houses the radial drive shaft which transfers power from the inlet gearbox to the transfer gearbox (TGB) mounted on the bottom of the frame.

ROTOR.—The compressor rotor (fig. 2-24) is a spool/disk structure with circumferential dovetails. The use of spools makes it possible for several stages of blades to be carried on a single piece of rotor structure. The seven major structural elements and three main bolted joints are as follows:

The first-stage disk, the second-stage disk (with integral front stub shaft), and the 3- through

9-spool stage are joined by a single bolted joint at stage 2.

The 3- through 9-spool stage, the stage 10 disk, and the 11- through 13-spool stage are bolted at the stage 10 joint.

The 11- through 13-spool (with its integral rear shaft) and the cantilevered 14- through 16-spool connect in a single bolted joint at stage 13.

An air duct, supported by the front and rear shafts, routes stage 8 air aft through the center of the rotor for pressurization of the B-sump seals.

Close vane-to-rotor spool and blade-to-stator casing clearances are obtained with metal spray-rub coating. Thin squealer tips on the blades and vanes contact the sprayed material and abrasive action on the tips prevents excessive rub while obtaining minimum clearance. The first-stage blades have midspan platforms to reduce blade tip vibration.

STATOR.—The compressor stator has four sections bolted together. The top and bottom cases are manufactured in matched sets. For

Figure 2-25.—Compressor stator.

clarity, figure 2-25 shows only the top two sections and the major components of the compressor stator. The front casing contains the IGVs and stages 1 through 11. The IGVs and the first six stages are variable to provide stall-free operation. The variable vanes are actuated by a pair of master levers (one on each side). The aft end of the master levers are attached to pivot posts at about the 10th stage on each side of the casing. Each of the lever’s forward ends is positioned by a hydraulic actuator which uses fuel oil as the actuating medium. The operation of the IGVs and variable stator vanes (VSVs) are covered later in this chapter. The remaining vanes are stationary. The rear casing contains the 12th through the 16th stages, which are also stationary.

Three bleed manifolds are welded to the stator casings. Eighth-stage air, used for sump seal pressurization and cooling, is extracted from inside the annulus area at the tips of the hollow eighth-stage vanes. Ninth-stage air, used for PT cooling, PT forward seal pressurization, and PT balance piston cavity pressurization, is extracted from between the ninth-stage vanes through holes in the vane bases. Thirteenth-stage air, used for cooling the second-stage HP turbine nozzle, is extracted from between the thirteenth-stage vanes through holes in the vane bases.

REAR FRAME.—The compressor rear frame (fig. 2-26) has an outer case, a hub containing the B sump, and 10 struts attaching the hub to the outer case. The outer case supports the

Figure 2-26.—Compressor rear frame.

combustor, the fuel manifold, 30 fuel nozzles, 2 spark igniters, and the first-stage HP turbine nozzle support. To provide the ship’s bleed air system with compressor discharge air, an internal manifold within the frame extracts air upstream of the combustion area and routes it through struts 3, 4, 8, and 9.

Compressor discharge air is also used for cooling the HP internal structures and the HP stage 1 and stage 2 blades. This will be addressed in more detail later. Six bore-scope ports, located in the case just forward of the mid flange, permit inspection of the

combustor, fuel nozzles, and the first-stage turbine nozzle.

Two borescope ports are provided in the aft portion of the case for inspection of the turbine blades and nozzles. The B sump contains the No.

4R and 4B bearings (R or no letter = roller, B = ball). The 4B bearing is the thrust bearing for the HP rotor system. The frame struts provide passage for lube oil, scavenge oil, sump vent, seal leakage (air leakage past the compressor discharge pressure (CDP) seals), and customer bleed air for masker, prairie, anti-icing, and engine starting services. The rear frame supports the aft end of

Figure 2-27.—LM2500 GTE combustor.

the compressor stator by the frame’s forward flange, the aft end of the compressor rotor by the No. 4R and 4B bearings, and the forward end of the HP turbine rotor by the 4R and 4B bearings.

Combustor Section

The LM2500 GTE combustor (fig. 2-27) is an annular type and has four major components riveted together-the cowl (diffuser) assembly, the dome, the inner liner, and the outer liner.

The cowl assembly and the compressor rear frame serve as a diffuser and distributor for the compressor discharge air. They furnish uniform airflow to the combustor throughout a large operating range. This provides uniform combustion and even-temperature distribution at the turbine. The combustor is mounted in the compressor rear frame on 10 equally spaced mounting pins in the forward (low temperature) section of the cowl assembly. These pins provide positive axial and radial location and assure centering of the cowl assembly in the diffuser passage. The mounting hardware is enclosed within the compressor rear frame struts so it will not affect airflow. Strength and stability of the cowl ring section are provided with a truss structure. The structure has 40 box sections welded to the cowl walls. The box sections also serve as aerodynamic diffuser elements. The cowl assembly leading edge fits within and around the compressor rear frame struts. This arrangement provides a short overall combustor system length.

Figure 2-28.—HP turbine.

Thirty vortex-inducing axial swirl cups in the dome (one at each fuel nozzle tip) provide flame stabilization and mixing of the fuel and air. The interior surface of the dome is protected from the high temperature of combustion by a cooling-air film of the 16th-stage air. Accumulation of carbon on the fuel nozzle tips is minimized by venturi-shaped spools attached to the swirler.

The combustor liners are a series of over-lapping rings joined by resistance-welded and brazed joints. They are protected from the high combustion heat by circumferential film cooling.

Primary combustion and cooling air enters through closely spaced holes in each ring. These holes help to center the flame and admit the balance of the combustion air. Dilution holes on the outer and inner liners provide additional mixing to lower the gas temperature at the turbine inlet. Combustor/turbine nozzle air seals at the aft end of the liners prevent excessive air leakage and also provide for thermal growth.

About 30 percent of the total airflow is used in the combustion process. To understand this, you need to know that the ideal fuel/air ratio for combustion is about 15 to 1 (15 parts of air to 1 part of fuel). The rated airflow of the LM2500 GTE is 123 lb/sec or 442,800 lb/hour. At rated power, the engine burns about 9,000 pounds of fuel per hour. At the ideal fuel/air ratio of 15 to 1, only 135,000 pounds of air per hour, is required (30.5 percent of 442,800).

The remaining 70 percent of the airflow is used for cooling, seal pressurization, and ship’s service use. This breaks down to 5.5 percent (maximum) used for ship’s service and about 0.5 percent for seal pressurization. The rest is used for cooling, the majority of which reenters the mass flow cycle.

Figure 2-29.—HP turbine rotor.

High-Pressure Turbine Section

The HP turbine section (fig. 2-28) has an HP turbine rotor, the first- and second-stage turbine nozzle assemblies, and the turbine mid frame. The turbine rotor extracts energy from the gas stream to drive the compressor rotor. The turbine rotor is mechanically coupled with the compressor rotor. The turbine nozzles direct the hot gas from the combustor onto the rotor blades at the best angle and velocity.

The turbine nozzles are contained in and supported by the compressor rear frame. The turbine mid frame, besides supporting the aft end of the turbine rotor, also supports the front end of the PT and contains the transition duct. The gas flows throughout this duct from the HP turbine section into the PT.

ROTOR.—The HP turbine rotor (fig. 2-29) has a conical forward shaft, two disks with blades and retainers, a conical rotor spacer, a thermal shield, and a rear shaft. The front end of the turbine rotor is supported at the compressor rotor rear shaft by the No. 4 bearings. The rear of the rotor is supported by the No. 5 bearing in the turbine mid frame (C sump).

Energy extracted from the hot combustion gases is transmitted to the compressor rotor through the turbine rotor forward shaft. Two air seals are on the forward end of the forward shaft.

The front seal helps prevent CDP air from enter-ing the sump. The other seal maintains CDP in the plenum formed by the rotor and combustor.

This plenum is a balance chamber that provides a corrective force that minimizes the thrust load on the No. 4B bearing.

High-Pressure Turbine Rotor Cooling.—The HP turbine rotor is cooled by a continuous flow of compressor discharge air. This air passes through holes in the first-stage nozzle support and in the forward turbine shaft. The air cools the inside of the rotor and both disks before passing between the dovetails and out to the blades. Figure 2-30 shows the airflow path for HP turbine rotor cooling.

Figure 2-30.—HP turbine rotor cooling.

Figure 2-31.—HP turbine rotor blade cooling.

High-Pressure Turbine Blade Cooling.—Both leading edge circuit provides internal convection stages of HP turbine blades are cooled by cooling by airflow through the labyrinth and out compressor discharge air (fig. 2-31). This air through the leading edge nose and gill holes.

flows through the dovetail and through blade Convection cooling of the trailing edge is provided shanks into the blades. First-stage blades are by air flowing through the trailing edge exit cooled by internal convection and external film holes. Second-stage blades are cooled by cooling. The convection cooling of the center area convection, with all the cooling air discharged

at the blade tips.