Introduction to Marine Gas Turbines

7/27/2019 Introduction to Marine Gas Turbines

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Although the words "lie", "him", and "his",are used sparingly in this manual to enhanceeomnumication, they are not intended to hegender driven nor to affront or discriminateagainst anyone reading Introduction to MarineGas Turbines, NAVHDTRA 10094.


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Tliis text is written to provide training support for personnel workingwith gas turbine propulsion systems. It is the first of a series of subjectmatter directed manuals which will address the field of gas turbinepropulsion technology in the U. S. Navy.

Personnel using this material to study for advancement in gas turbinefields should also study texts which will provide the basic foundations ofmechanical sciences, such as Basic Machines, NAVPERS 106 24-A; FluidPower, NAVPERS 16193-B; and at least one conventional rate trainingmanual, such asEngineman 3&2, NAVPERS 10541-B.

The text provides a general mechanical and functional description of amarine gas turbine propulsion system, using the LM 2500 turbine installationas an example.

The text was prepared by the Naval Education and Training ProgramDevelopment Center, Pensacola, Florida. Technical assistance was providedby Naval Sea Systems Command and Service Schools Command, GreatLakes, 111.

Stock Ordering No.0502-LP-050-4700

Revised 1978

Published byNAVAL EDUCATION AND TRAINING SUPPORT COMMAND

UNITED STATESGOVERNMENT PRINTING OFFICEWASHINGTON, D. C: 1978


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THE UNITED STATES NAVYGUARDIAN OF OUR COUNTRY

The United States Navy is responsible for maintaining control of thesea and is a ready force on watch at home and overseas, capable ofstrong action to preserve the peace or of instant offensive action towin in war.It is upon the maintenance of this control that our country's gloriousfuture depends; the United States Navy exists to make it so.

WE SERVE WBTH HONORTradition, valor, and victory are the Navy's heritage from the past. Tothese may be added dedication, discipline, and vigilance as thewatchwords of the present and the future.At home or on distant stations we serve with pride, confident in therespect of our country, our shipmates, and our families.Our responsibilities sober us; our adversities strengthen us.Service to God and Country is our special privilege. We serve withhonor.

THE FUTURE OF THE NAVYThe Navy will always employ new weapons, new techniques, andgreater power to protect and defend the United States on the sea,under the sea, and in the air.Now and in the future, control of the sea gives the United States hergreatest advantage for the maintenance of peace and for victory inwar.Mobility, surprise, dispersal, and offensive power are the keynotes ofthe new Navy. The roots of the Navy lie in a strong belief in thefuture, in continued dedication to our tasks, and in reflection on ourheritage from the past.Never have our opportunities and our responsibilities been greater.


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CONTENTS

CHAPTER Page1. Development of Gas Turbine Engines 12. Engine Types and Construction 153. Starting Systems 444. Fuels and Lubricants 515. Automated Central Operating System 65

INDEX 81


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CREDITS

The illustrations indicated below are included in this publication throughthe courtesy of the following companies. Permission to reproduce theseillustrations must be obtained from the original source.

Source Fi6ures

General Electric Co. 5-1 , 5-3, 5-4, 5-5, 5-75-16, 5-17

Henschel Corp. 5 '8


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CHAPTER 1MARINE GAS TURBINE PROPULSION SYSTEMS

This chapter is intended to develop yourunderstanding of the history and developmentof gas turbines, to familarize you with the basicconcepts used by gas turbine designers, and tointroduce you to the principal components ofgas turbines. You will follow discussions of howthe Brayton cycle describes the thermodynamicprocesses in a gas turbine, how variousconditions and design limitations affect gasturbine performance, and how the gas turbinedevelops and uses hot gases under pressure. Youwill also learn a large amount of nomenclaturerelated to gas turbines and gas turbinetechnology.

HISTORY AND BACKGROUNDUntil recent years it has not been possible to

separate gas turbine technology and jet enginetechnology. The same people have worked inboth fields, and the same sciences have beenapplied to both types of engines. Recently, thejet engine has been used more exclusively as apart of aviation, and the gas turbine has beenused for electric generation, ship propulsion, andeven experimental automobile propulsion andsome successful racing cars. Even now, manyoperational turbine power plants use an aircraftjet engine as a gas generator, adding a powerturbine and transmission to complete the plant.

In nature, the squid was using jet propulsionlong before our science thought of it. Therewere examples of the reaction principle in earlyhistory; however, practical applications of thereaction principle have occurred only recently.This delay is due to slow progress of technicalachievement in engineering, fuels, andmetallurgy (the science of metals).

Between the first and third centurieHero, a scientist in Alexandria, Egypt, dewhat is considered to be the first "jet eMany sources credit him as the inWhether or not this is true, such a deviceas the "aeolipile" (fig. 1-1) is mentiosources dating back as far as 250 B.C.

Throughout the course of history, texamples of other well-known scientistthe principle of expanding gases to pwork. Among these were inventions of Leda Vinci (fig. 1-2) and Giovanni Bran1-3).

Figure 1-1. Hero's aeolipile.


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INTRODUCTION TO MARINE GAS TURBINES

277.5Figure 1-2. DaVinci's chimney jack.

20TH CENTURYDEVELOPMENTThe patented application for the gas

as we know it today was submitted in 1another Englishman, Sir Frank Whittlpatent was for a jet aircraft engine. Usown ideas along with the contributionsscientists as Coley and Moss, Whittleseveral failures, came up with a workiturbine engine.

You should note that up to this timthe early pioneers in the gas turbine fieEuropean-born or oriented .American Development

The United States did not go intoturbine field until late in 1941 whenElectric was awarded a contract to buAmerican version of a foreign-designedengine. The engine and airframe were boin one year, and the first jet aircraft wasin this country in October 1942.

In late 1941 Westinghouse Corpawarded a contract to design and builscratch the first all-American gas turbineTheir engineers designed the first axicompressor and annular combustion chBoth of these ideas, with minor changes,basis for the majority of contemporaryin use today.

Figure 1-3. Branca's jet turbine.277.J6

In the 1680's Sir Isaac Newton described thelaws of motion on which are based all devicesthat use the theory of jet propulsion. Newton'ssteam wagon is an example of the reactionprinciple (fig. 1-4).

The first patent for a design that used thethermodynamic cycle of the modern gas turbine,also suggested as a means of jet propulsion, wassubmitted in 1791 by John Barber, anEn lishman. Picture 1-4. Newton's steam waaon.


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Chapter 1 -MARINE GAS TURBINE PROPULSION SYSTEMSMarine Gas Turbines

The concept of using a gas turbine to propela ship goes back to 1937 when a Pescara freepiston gas engine was used experimentally with agas turbine. The free piston engine, or "gasifier"(fig. 1-5-) ,is a form of diesel engine, using aircushions instead of a crankshaft to return thepistons. It was an effective producer ofpressurized gases, and the German Navy used itin their submarines during World War II as an aircompressor. In 1953 the French placed inservice two small vessels powered by a freepiston engine-gas turbine combination. In 1957the liberty ship, WILLIAM PATTERSON,having six free piston engines driving twoturbines, went into service on a transatlanticrun.

Over the same period there were a numberof applications of the use of a rotary gasifier todrive a main propulsion turbine. The gasifier, orcompressor, was usually an aircraft jet engine orturboprop front end. In 1947 the Motor GunBoat 2009 of the British Navy used a 2,500 hpgas turbine to drive the center of three shafts. In1951 the tanker AURIS, in an experimentalapplication, replaced one of four diesel engineswith a 1,200 hp gas turbine. In 1956 the JOHNSERGEANT had a remarkably efficientinstallation which gave a fuel consumption rateof .523 pounds per hp/hr. The efficiency waslargely due to use of a regenerator whichrecovered heat from the exhaust gases.

/INTAKE VALVE COMPRESSED AIR BLEED

CYLINDER INTAKE PORTS

^BOUNCECHAMBEREXHAUST TOGAS TURBINE

277.8Figure 1-5. Free piston engine.

By the late 1950's the gas turbineengine was becoming widely used, mosEuropean navies. All the applications cothe gas turbine plant with another, convenform of propulsion machinery. The gaswas used for high-speed operation, aconventional plant was used for cruisimost common arrangements were the C(Combined Diesel or Gas) or the C(Combined Diesel and Gas) Systems.engines give good cruising range and relbut they have a disadvantage whenantisubmarine warfare. Their low-frsounds travel great distances throughmaking them easily detected by passiveTo reduce low frequency sound, steam thave been combined in the COSAG (CoSteam and Gas) configuration, but thesemore personnel to operate and do not hlong range of the diesel combinations. Aconfiguration that has been successfulCOGOG (Combined Gas or Gas). TheCounty class destroyers use the 4,500 hgas turbine engine for cruising and thRoyce Olympus, a 28,000 hp engine, fspeed.

The U.S. Navy entered the mariturbine field with the Asheville classgunboats. These ships have the Cconfiguration, with two diesel engicruising, and a General Electric LM 1turbine to operate at high speed. As a rthe increasing reliability and efficiencygas turbine designs, the Navy has now dand -is building destroyers and frigates whbe entirely propelled by gas turbine enginADVANTAGES ANDDISADVANTAGES

The gas turbine, when compared ttypes of engines, offers many advantagreatest asset is its high power to weighThis has made it, in the forms of turboturbojet engine, the preferred engine forCompared to the gasoline piston enginehas the next best power-to-'characteristics, the gas turbine operacheaper and safer fuel. The smoothnessgas turbine, compared with recip


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aircraft, because less vibration reduces strains onthe air frame. In a warship, the lack oflow-frequency vibration of gas turbines makesthem preferable to diesel engines because thereis less noise for a submarine to pick up at longrange. Modern production techniques have madegas turbines economical in terms ofhorsepower-per-dollar on initial installation, andtheir increasing reliability makes them acost-effective alternative to steam turbine ordiesel engine installation. In terms of fueleconomy, modern marine gas turbines cancompete with diesel engines and may be superiorto boiler/steam turbine plants, when these areoperating on distillate fuel.

However, there are some disadvantages togas turbines. Since they are high-performanceengines, many parts are under high stress.Improper maintenance and lack of attention todetails of procedure will impair engineperformance and may ultimately lead to enginefailure. A pencil mark on a compressor turbineblade or a fingerprint in the wrong place cancause failure of the part. The turbine takes inlarge quantities of air which may containsubstances or objects that can harm. Most gasturbine propulsion control systems are verycomplex because several factors have to becontrolled, and numerous operating conditionsand parameters must be monitored. The controlsystems must react quickly to turbine operatingconditions to avoid casualties to the equipment.Gas turbines produce high-pitched loud noiseswhich can damage the human ear. In shipboardinstallations special soundproofing is necessary,adding to the complexity of the installation andmaking access for maintenance more difficult.

From a tactical standpoint, there are twomajor drawbacks to the gas turbine engine. Thefirst is the large amount of exhaust heatproduced by the engines. Most current antishipmissiles are heat-seekers, and the infraredsignature of a gas turbine makes an easy target.Countermeasures such as exhaust gas coolingand infrared decoys have been developed toreduce this problem.

The second tactical disadvantage is therequirement for depot maintenance and repair

repaired in place on the ship and mremoved and replaced by rebuilt enganything goes wrong. Here too, desireduced the problem, and an engine chabe accomplished wherever crane servicNavy tender is available and the replaengine can be obtained.FUTURE TRENDS

As improved materials and designsoperation at higher combustion tempeand pressures, gas turbine efficiencincrease. Even now, gas turbine main proplants offer fuel economy and installationo greater than diesel engines. Initial colower than equivalent steam plants whicdistillate fuels. Future improvements maygas turbines the best choice for nonpropulsion of ships up to cruiser size.

At present, marine gas turbines usejet engines for gas generators. These aremodified for use in a marine envirparticularly in respect to corrosion resistamarine gas turbines become more widelspecific designs for ships may evolve.compressors may be heavier and bulkieaircraft engines and take advantaregenerators to permit greater efficiency.

It is unlikely that large gas turbinesmade so simple and rugged that theyoverhauled in place, so they willtechnical support from shore. It is possairlift replacement engines if necessary,turbine ships can operate and be rworldwide on a par with their stediesel-driven counterparts.

The high power-to-weight ratiosturbine engines permit the developmhigh-performance craft such as hydrofoisurface effect vehicles. Because of thespeed and ability to carry formidable wsystems, these craft will be seen in incnumbers in our fleet. In civilian vhydrofoils have been serving for many ytransport people on many of thewaterways. Hovercraft are finding inemployment as carriers of people. Thcapable of speeds up to 100 knots, and, i


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Chapter 1 -MARINE GAS TURBINE PROPULSION SYSTEMSgradients are not too steep, they can reachpoints inland after crossing seas, marshy terrain,or almost any other level area.

GAS TURBINE OPERATIONA gas turbine engine is composed of three

major sections:1. Compressor(s)2. Combustion chamber(s)3. Turbine wheel(s)A brief description of what takes place in a

gas turbine engine during operation follows (seefig. 1-6): Air is taken in through the air inletduct by the compressor which raises pressureand temperature. The air is then discharged intothe combustion chamber(s) where fuel isadmitted by the fuel nozzle(s). The fuel-airmixture is ignited by igniter(s) and combustiontakes place. Combustion is continuous, and theigniters are deenergized after a brief period oftime. The hot and rapidly expanding gases aredirected towards the turbine rotor assembly.

Kinetic and thermal energy are extractedturbine wheel(s). The action of the gasesthe turbine blades causes the turbine asto rotate. The turbine rotor is connectedcompressor which rotates with the turbiexhaust gases then are discharged throexhaust duct.

Since approximately 75% of thedeveloped by a gas turbine engine is udrive the compressor and accessories, oncan be used to drive a generator or to pship.

LAWS AND PRINCIPLESTo understand basic engine theormust be familiar with the physics concep

in the operation of a gas turbine engine.following paragraphs we have compiled adefinitions of laws and principles as theto the work you will be doing in gas tuexplained each of them, and then demonshow they apply to a gas turbine.BERNOULLI'S PRINCIPLE: If a fluidthrough a tube reaches a constricti

COMPRESSOR ASSEMBLYA COMBUSTION ASSEMBLYA TURBINE ASSEMBLYA

EXHAUST GASES

Figure 1-6. Gas turbine operation.


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narrowing of the tube, the velocity of fluidflowing through the constriction increases andthe pressure decreases.

BOYLE'S LAW: The volume of an enclosed gasvaries inversely with the applied pressure,provided the temperature remains constant.

CHARLES' LAW: If the pressure is constant,the volume of an enclosed dry gas varies directlywith the absolute temperature.NEWTON'S LAW: The first law stales that abody at rest tends to remain at rest, and a bodyin motion tends to remain in motion. Thesecond law states that an unbalance of force ona body tends to produce an acceleration in thedirection of the force, and that the acceleration,if any, is directly proportional to the force andinversely proportional to the mass of the body.Newton's third law states that for every actionthere is an equal and opposite reaction.PASCAL'S LAW: Pressure exerted at any pointupon an enclosed liquid is transmittedundiminished in all directions.BERNOULLI'S PRINCIPLE

Consider the system illustrated in figure 1-7.Chamber A is under pressure and is connectedby a tube to chamber B which is also underpressure. Chamber A is under static pressure of100 psi. The pressure at some point, point X inthis case, along the connecting tube consists of avelocity pressure of 10 psi exerted in a directionparallel to the line of flow, plus the unused

static pressure of 90 psi, which obeylaw and operates equally in all directionfluid enters chamber B from the cspace, it is slowed down, and, in sovelocity head is changed back to pressThe force required to absorb the fluidequals the force required to startmoving originally, so that the static pchamber B is again equal to that in calthough it was lower at intermediate

The illustration (fig. 1-7) disregardand is therefore not encounteredpractice. Force or head is also reovercome friction but, unlike inertia eforce cannot be recovered again althenergy represented still exists someheat. Therefore, in an actual system thin chamber B would be less than in cby the amount of pressure used in ovfriction along the way.

At all points in a system, therestatic pressure is always the originpressure LHSS any velocity head at thquestion and LESS the friction headin reaching that point. Since both veloand friction represent energy which cthe original static head, and since enerbe destroyed, the sum of the stavelocity head, and friction at any poisystem must add up to the original stThis, then, is Bernoulli's principle, morstated: If a fluid flowing through a tuba constriction, or narrowing of thevelocity of fluid flowing throconstriction increases, and thedecreases. Bernoulli's principle gov

100 IBS. PER SQ. IN.

Figure 1-7. Relation of static and dynamic factors-Bernoulli's principle.


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Chapter 1 -MARINE GAS TURBINE PROPULSION SYSTEMSrelationship of the static and dynamic factorsconcerning fluids, while Pascal's law governs thebehavior of the static factors when taken bythemselves.

BOYLE'S LAWCompressibility is an outstanding

characteristic of gases. The English scientistRobert Boyle was among the first to study thischaracteristic, which he called the "springinessof air." By direct measurement, he discoveredthat when the temperature of an enclosedsample of gas was kept constant and the pressuredoubled, the volume was reduced to half theformer value and, as the applied pressure wasdecreased, the resulting volume increased. Fromthese observations, he concluded that for aconstant temperature the product of the volumeand pressure of an enclosed gas remainsconstant. This became Boyle's law, which isnormally stated: "The volume of an encloseddry gas varies inversely with its pressure,provided the temperature remains constant."

You can demonstrate Boyle's law byconfining a quantity of gas in a cylinder whichhas a tightly fitted piston. Then apply force tothe piston so as to compress the gas in thecylinder to some specific volume. If you doublethe force applied to the piston, the gas willcompress to one-half its original volume, asindicated in figure 1-8.

In formula or equation form (V = volume;P = pressure) when V 1 and P 1 are the originalvolume and pressure and V2 and P 2 are therevised volume and pressure, this relationshipmay be expressed

V 1 P 1 =V 2 P2or

V2 P,Example: 4 cubic feet of nitrogen are under

a nressure of 1 00 nsie. The nitro en is allowed

HUE

GAS

Figure 1-8. Gas compressed to half its originalby a double force.

to expand to a volume of 6 cubic feet.the new gage pressure? Remember togage pressure to absolute pressuadding 14.7.

Substitute

4X(100+ 14.7) = 6 XP 2P - 4X 114 -72 6P2 = 76.47 psia

(absolute pressur

Convert absolute pressure to gage pressur76.47-14.761 .77 psig (gage pressure)

Changes in the pressure of a gas also afdensity. As the pressure increases, itsdecreases; however, there is no changeweight of the gas. Therefore, the weightvolume (density) increases. So it followsdensity of a gas varies directly as the prethe temoerature is constant.


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Jacques Charles, a French scientist, providedmuch of the foundation for the modern kinetictheory of gases. He found that all gases expandand contract in direct proportion to the changein the absolute temperature, provided thepressure is held constant. In equation where V 1and V 2 refer to the original and final volumes,and T! and T 2 indicate the correspondingabsolute temperatures, this part of the law maybe expressed

ViT2 =V2 T 1

temperature.)

or

V,

Since any change in the temperature of a gascauses a corresponding change in volume, it isreasonable to expect that if a given sample of agas were heated while confined within a givenvolume, the pressure should increase. By actualexperiment, it was found that for each 1 Cincrease in temperature, the increase in pressurewas approximately ^73 of the pressure at C.Because of this fact, it is normal practice to statethis relationship in terms of absolutetemperature. In equation form, this part of thelaw becomes

PiT2 =P2 T 1or

PIT,

In words, this equation states that with aconstant volume, the absolute pressure of anenclosed gas varies directly with the absolutetemperature.

Examples of Charles' law: A cylinder of gasunder a pressure of l,800psig at 20 C is leftout in the sun and heats up to a temperature of55 C. What is the new pressure within the

or

1814.7 psia2031.47 psia

T,T2

292 C absolute328 C absolute

NEWTON'S FIRST LAWNewton's first law states that a body

tends to remain at rest, and a body intends to remain in motion. This lawdemonstrated easily in every day usexample, a parked automobile willmotionless until some force causes it tobody at rest tends to remain at rest. Theportion of the law a body in motion tremain in motion-can be demonstrateda theoretical sense. The same car plmotion would remain in motion ifresistance could be removed, if there wfriction at all encountered in the bearingsthe surface on which the vehicle was twere perfectly level.NEWTON'S SECOND LAW

Newton's second law states tunbalance of force on a body tends toan acceleration in the direction of the fothe acceleration, if any, is directly propoto the force and inversely proportionalmass of the body. This law can be explathrowing a common softball. The force rto accelerate the ball to a rate of 50would have to be doubled to obtacceleration rate of 100 ft/sec 2 . Howevermass of the ball were doubled, (do notmass with weight) the original acceleratof 50 ft/sec2 would be cut in half to 25This law can be explained mathema(A = acceleration; F = force; M = mass)

-.M


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Chapter 1 -MARINE GAS TURBINE PROPULSION SYSTEMSNEWTON'S THIRD LAW

Newton's third law states that for everyaction there is an equal and opposite reaction.You have demonstrated this law if you have everjumped from a boat up to a dock or a beach.The boat moved opposite to the direction youjumped. (See fig. 1-9).

The recoil from firing a shotgun is anotherexample of action-reaction. We can demonstratethis law with the same factors used in the secondlaw in the equation

277.10Figure 1-9. Newton's third law of motion.

In an airplane, this means the greamass of air handled by the engine, the maccelerated by the engine and the greaforce built up to thrust the plane forwargas turbine, by adding more and progrlarger power turbine wheels, the thrustcan be absorbed by the turbine rotconverted to mechanical energy.

BASIC ENGINE THEORYTwo factors are required for

operation of a gas turbine. One is expreNewton's third law, and the otherconvergent-divergent process. Convergentapproaching nearer together, as the innof a tube that is constricted. Divergentmoving away from each other, as the innof a tube that flares outward.

Bernoulli's principle is used in thisThe venturi of the common autcarburetor is a common example of Berprinciple and the convergent-divergentNow let us describe a prdemonstration of how a gas turbine o(see figure 1-10, foldout at the endchapter).

A blown-up ballon (fig. 1-1 OA) doesuntil the trapped air is released. The air erearward causes the balloon to move(Newton's third law). (See fig. 1-1 OB).

If we could keep the balloon full ofballoon would continue to move forwarfig. 1-10C.)

If a fan or pinwheel is placed instream, the pressure energy and velocitywill cause it to rotate and it can then bedo work. (See fig. 1-10D.)

By replacing the balloon with acontainer (mounted in one place) and fwith air from a fan or series of fans (lothe air opening and driven by some soucan use the discharge air to turn a fan atto do work. (See fig. 1-10E.)

If fuel is added and combustion occgreatly increase both the volume of air (law) and the velocity with which it pass


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fan will produce (See fig. 1-1 OF.)The continuous pressure created by the inlet

fan, or compressor, prevents the hot gases fromgoing forward.

Next, if we attach a shaft to the compressorand extend it back to a turbine wheel we have asimple gas turbine that can supply power to runits own compressor and still provide enoughpower to do useful work, such as drive agenerator or propel a ship. (See fig. 1-10G.)

By comparing figure 1-1 OH with figure1-1OG you can see that a gas turbine is verysimilar to our balloon turbine. Recall the threebasic parts of a gas turbine mentioned earlier:

1 . Air is taken in through the air inlet ductby the compressor where it is raised in pressureand discharged into the combustion chamber.

2. Fuel is admitted into the combustionchamber by the fuel nozzle(s). The fuel-airmixture is ignited by igniter(s) and combustionoccurs.

3. The hot and rapidly expanding gases aredirected aft through the turbine rotor assemblywhere thermal and kinetic energy are convertedinto mechanical energy. The gases are thendirected out through the exhaust duct.

THEORETICAL CYCLES

air is drawn in at constantAs the piston moves upincreases and the volume dThen the fuel is ignited whiincrease in pressure (Linpressure forces the pistonin a drop in pressure and an(Line D-E). The exhaust vthe combustion charge wipressure at constant volumpiston rises, forcing the exconstant pressure (Line B-cycle will begin again. Figushows how the Otto cycleand returns to the same cond

The Brayton cycle canexplained. (See fig. 1-1 IB.)at atmospheric pressure a(point A). As the air pcompressor, it increasesdecreases in volume (Linecombustion occurs at consthe increased temperaturincrease in volume (Lineconstant pressure and incrthe turbine and expand thrpass through the turbine rokinetic and thermal enerenergy. The expanding sicauses further increase in

Let's dwell a little more on cycles andtheory before we go into construction anddesign. A cycle is a process that begins withcertain conditions, progresses through a series ofadditional conditions, and returns to the originalconditions.

The gas turbine engine operates on theBRAYTON CYCLE. The OTTO CYCLE, used ingasoline engines, is one of constant volume whilecombustion occurs, and the Brayton cycle is onewhere combustion occurs at constant pressure.In reciprocal ,g gasoline or diesel engines allevents take place within one unit. That is,intake, compression and combustion as well asexpansion and exhaust, take place within thecylinder. In gas turbines a specific component isdesigned to perform each function separately.

VOLUMEOTTO CYCLE

(GASOLINE ENGINE)A

Figure 1-11.-The Otto cycle10


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released through the stack with a large drop involume and at constant pressure (Line D-A). Thecycle is completed and commences again atpoint A.

In the reciprocating engine each event occursin one location at independent intervals, i.e., nomore than one event can occur at any one time.In the gas turbine engine all events intake,compression, combustion, exhaust areoccurring simultaneously, but at differentlocations.

OPEN ANDCLOSED CYCLESMost internal-combustion engines operate on

an open engine cycle, meaning the working fluidis taken in, used, and discarded. There are somegas turbines that operate on a semiclosed cycle.They use a regenerator such as used on the gasturbine ship JOHN SERGEANT. The gasturbines you will encounter in the Navy operateon the open cycle.

In the open cycle all the working fluid passesthrough the engine only once. The open cycleoffers the advantages of simplicity and lightweight.

The third classification of cycles is theclosed cycle, where energy is added externally.The typical ship's steam plant is an example of aclosed cycle system.CONVERGENT-DIVERGENT PROCESS

There are several pressure, volume, andvelocity changes that occur within a gas turbineduring operation. The convergent-divergentprocess is an application of Bernoulli's principle.(If a fluid flowing through a tube reaches aconstriction or narrowing of the tube, thevelocity of the fluid flowing through theconstriction increases and the pressure decreases.The opposite is true when the fluid leaves theconstriction; velocity decreases and pressureincreases.) Boyle's law and Charles' law alsocome into play during this process. Boyle's law:The volume of any dry gas varies inversely withthe applied pressure, provided the temperature

constant, the volume of dry gas varieswith the absolute temperature.Now, let's apply these laws to t

turbine. Please refer to figure 1-12.Air is drawn into the front

compressor. The rotor is so constructed tarea decreases toward the rear. Thisconstruction gives a convergent area (AEach succeeding stage is smaller, which ipressure and decreases velocity (Bernoulli)

Between each rotating stage is a stastage or stator. The stator partially convervelocity to pressure and directs the airnext set of rotating blades.

Because of its high rotational speerotor imparts velocity to the air. Eachrotor and stator blades constitutes a pstage. Also, there is both a pressure inceach stage, and a reduction in volume (

This process continues at each stage uair charge enters the diffuser. (See arfigure 1-12.) There is a short area in thewhere no further changes takes place. Ascharge approaches the end of the diffuswill notice that the opening flares (doutward. At this point, the air loses vand increases in volume and pressure. Thvelocity energy has become pressurewhile pressure through the diffuser has reconstant. The reverse of Bernoulli's pand Boyle's law has taken place. The acthe compressor's continuously forcing mthrough this section at a constant rate maconstant pressure. Once the air iscombustor, combustion takes place at cpressure. After combustion there isincrease in the volume of the air and combgases (Charles' law).

The combustion gases go rearward topartially by velocity imparted by the compand partially because area C is a lower parea. The end of area C is the turbinesection. Here you will find a decrease in pand an increase in velocity. The high-vhigh-temperature, low-pressure gases are dthrough the inlet nozzle to the first stagturbine rotor (area D). The high-vhigh-temperature gases cause the rotor to

11


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Chapter 1 -MARINE GAS TURBINE PROPULSION SYSTEMSNow refer back to figure 1-1 IB. Air enters

the intake at constant pressure (point A) and iscompressed as it passes through the compressor(line A-B in fig. 1-1 IB and area A in fig. 1-12).Between the end of area B and the beginning ofarea C in figure 1-12, combustion occurs andvolume increases (fig. 1-1 IB line B-C). As thegases pass through area D (fig. 1-12), the gasesexpand with a drop in pressure and an increasein volume (fig. 1-1 IB line C-D). The gases aredischarged to the atmosphere through theexhaust duct at constant pressure (fig. 1-1 IBline D-A and fig. 1-12 exhaust). At this pointyou should have a clear understanding of how asimple gas turbine works.

ADIABATIC COMPRESSIONIn the ideal gas turbine, the air enters the

compressor and is compressed adiabatically. Anadiabatic stage change is one in which there is notransfer of heat to or from the system while theprocess is occurring. In many real processes,adiabatic changes can occur when the process isperformed rapidly. Since heat transfer isrelatively slow, any rapidly performed processcan approach an adiabatic state. Compressionand expansion of working fluids are frequentlyachieved very nearly adiabatically.

Figure 1-13 depicts the pressure-temperaturegraph for a simple gas turbine. During operationthe work produced by the compressor turbine

COMBUSTIONBURNING 3

'ATMOSPHERIC1 PRESSURE

EXHAUSTTEMPERATURE

277.121-1*3 f5ac tnrhino nroccuro t mnoratura nranh

rotor is almost the same amount as threquired by the compressor. The masavailable to the compressor turbine is absame as the mass flow handled bcompressor. Therefore, the heat of comprwill closely equal the heat of expansion,allowances for factors such as bleed air, pof fuel added, and heat loss to turbine par

As the high-temperature, high-pressurenter the turbine section, they expand sothat there is relatively little chantemperature of the gases. The netavailable from the turbine is the difbetween the turbine-developed power apower required to operate the compressorEFFECT OF AMBIENTTEMPERATURE

The power and efficiency of a gasengine is affected by both outside andvariables. Air has volume which isaffected by its temperature. As the tempdecreases, the volume of air for a givdecreases and its density incrConsequently, the mass weight ofincreases which in turn increases efbecause less energy is needed to achisame compression at the combustion chAlso cooler air causes lowertemperatures. The resulting temperaturesturbine life. For example, a propulsiturbine is operating at 100% gas generatowith 100% power turbine speed at an a(external air) temperature of 70 F.temperature were increased to 1 20volume of air would increase and thweight would decrease. Since the amountadded is limited by the inlet temperatturbine will withstand, the mass weighcannot be achieved; the result is a losspower available for work. The plant mayto produce only 90% to 95% of ithorsepower.

On the other hand, if the atemperature were to drop to F, the voair would decrease, and the mass weightincrease. Since the mass weight is increaheat transfer is better at hi her oressure. l


20/92

INTRODUCTION TO MARINE GAS TURBINESis needed to increase volume; the result is aheavier mass of air at the required volume. Thissituation produces quite an efficient power plantwith a gas generator speed of 85% to 90% and apower turbine speed of 1 00%. In the case of aconstant speed engine such as used on agenerator set, the differences in temperature willshow up on exhaust gas temperature and, insome cases, on the load the engine will pull. Forinstance, on a hot day of 120 F, the engine ona 300 kW generator set may be able to pull only275 kW due to limitations on exhaust or turbineinlet temperature. On a day with F ambienttemperature, the same engine will pull 300 kWand have an exhaust or turbine inlet temperaturethat may well be more than 100 Fahrenheitlower than average. Here again, less fuel isneeded to increase volume and a greater massweight flow, which in turn makes the plant moreefficient.COMPRESSOR CLEANLINESS

Another factor that will have a great effecton performance is the condition of thecompressor. A clean compressor is essential toefficiency and reliability. During operation atsea the compressor will ingest salt spray that is

present in the air. Over a period of time,will build up in the compressor. Salt brelatively slow and will occur more on tblades and the compressor case than onparts. Centrifugal force tends to scontaminants off the rotor blades.rapidly increases contaminationcompressor. Any oil ingested into thcoats the compressor with a film whiany dust and other foreign matter suspthe air. The dust and dirt absorb moretraps more dirt, etc. If left unattenbuildup of contamination will lead to aof the compressor and a restricted aiturn, gradually more fuel is required stemperatures will rise until loss of podamage to the turbine mayContamination, if not controlled, cancompressor surge during light off.In this chapter you have been intromany terms and concepts that willbasis for the discussions and descriptiofollow in the text. If you do notunderstand the temperature-prelationships in a simple gas turbine atyou would do well to re-read the last pachapter before continuing on to thewhich follows.


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22/92


23/92

CHAPTER 2

ENGINE TYPES AND CONSTRUCTIONThere are several different types of gas

turbines in use: SINGLE SHAFT, SPLITSHAFT, and TWIN SPOOL. Of these, the singleshaft and split shaft are the most common in usein naval vessels. We will mention the twin spooltype and give a brief description. The USCGHamilton class cutters use the Pratt-WhitneyFT-4 twin spool gas turbine.

In current U.S. Navy service the single shaftengine is used primarily for driving ship's servicegenerators, and the split shaft engine is used formain propulsion as a variety of speed ranges areencountered.

Figure 2-1 is a block diagram of a singleshaft gas turbine. In the engine illustrated, the

power output shaft is connected directlysame turbine rotor that drives the compIn most cases, there is a speed decrereduction gear between the rotor and theoutput shaft; however, there is still a mecconnection throughout the entire engine.

In the split shaft engine (fig. 2-2), themechanical connection betweegas-generator turbine and the powerWith this type of engine the output speedvaried by varying the generator speedunder certain conditions the gas generarun at a reduced rpm and still provide mapower turbine rpm which greatly improveconomy and also extends the life of

STARTERCOMPRESSOR SHAFT TURBINE

PROPULSIONPOWERCOUPLING=0

ATMOSPHERICAIR INTAKE

EXHAUST TOATMOSPHERE

Figure 2-1. Single shaft engine.

15


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GAS -GENERATOR SECTION POWER TURBINE

STARTER

AIR INTAKE EXHAUST

Figure 2-2. Split shaft engine.

generator turbine. The starting torque requiredis lowered appreciably due to the fact that thepower turbine, reduction gears, and output shaftremain stationary until the gas generator reachesapproximate idle speed. Another feature is thatin a multishaft marine propulsion plant whereone design (clockwise rotation orcounterclockwise rotation) of gas generator canbe used on either shaft, the gas generator rotatesonly one way; however, the power turbine canbe made to rotate either way by changing thepower turbine wheel and nozzles. Thearrangement shown in figure 2-2 is typical forpropulsion gas turbines aboard the DD-963 andFFG-7 class ships.

Another type of turbine is the twin spool,sometimes referred to as a multistage gasturbine. In the twin spool engine there are twoseparate compressors and two separate turbinerotors. They are referred to as L.P. compressorand turbine rotor and H.P. compressor andturbine rotor. (See fig. 2-3.) The L.P.compressor and turbine are connected by a shaftwhich runs through the hollow shaft that

connects the H.P. turbinecompressor. The starter drives theduring light off. The power turthe same as in the split shaft envolume of air can be handled assingle or split shaft engine; howevhas more moving parts, and toverall dimensions and complexiengine less desirable for ship's prthe split shaft engine.

CLASSIFICATION BYCOMPRESSOR TYPEGas turbines are also

compressor type, according to ththe flow of air through the compreprincipal types are centrifugal fflow. The centrifugal compressorthe center or eye of the impellerit around and outwards. In the axthe air is compressed whileoriginal direction of flow parallelthe compressor rotor.


25/92

Chapter 2-ENGINE TYPES AND CONSTRUCTION

GAS-GENERATOR SECTION POWER TURBINESECTION

COMPRESSORSHAFT-L.P ELEMENT

-J:

SHAFT-H.P. ELEMENTH.R ELEMENT

STARTER

TURBINE

L.R ELEMENT H.PELEMENT L.RELEMENT

POWERTURBINE

U;

PROPUPOWCOUP

Figure 2-3. Twin spool engine.

CENTRIFUGAL COMPRESSORThe centrifugal compressor is usually locatedbetween the accessory section and the

combustion section. The basic compressorsection consists of an impeller, diffuser, andcompressor manifold. The diffuser is bolted tothe manifold and often the entire assembly isreferred to as the diffuser. For ease ofunderstanding we shall treat each unitseparately.The impeller may be either single entry ordual entry (fig. 2-4). The principal differencesbetween the single entry and dual entry are thesize of the impeller and the ductingarrangement. The single entry impeller permitsconvenient ducting directly to the inducer vanesas opposed to the more complicated ductingneeded to reach the rear side of the dual entryt e. Althou h sli htl more efficient in

receiving air, single entry impellers mustgreater diameter to provide sufficient airincreases the overall diameter of the engin

Dual entry impellers are smaller in dand rotate at higher speeds to ensure suairflow. Most gas turbines of present dayuse the dual entry compressor to reducediameter. A plenum chamber is also requidual entry compressors since the air musthe engine at almost right angles to theaxis. The air must surround the comprepositive pressure before entering the compto give positive flow.

Principles of Operation

The compressor draws in the enterinthe hub of the im eller and acceler


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COMPRESSORMANIFOLD

(A) ELEMENTS OF A SINGLE ENTRY CENTRIFUGALCOMPRESSOR; AIR OUTLET ELBOW WITH TURN-ING VANES FOR REDUCING AIR PRESSURELOSSES.

COMPRESSORREAR INDUCERCOMPRESSORFRONT INDUCER

COOLINGIMPELLERCOMPRESSORCOUPLING

CENTERBEARINGFRONT BEARING

COMPRESSOR SHAFT(B) DUAL ENTRY COMPRESSOR

203.19:20Figure 2-4. Centrifugal compressors.

radially outward by means of centrifugal forcethrough the impeller. It leaves the impeller at ahigh velocity low pressure and flows through thediffuser. (See fig. 2-4A.) The diffuser convertsthe high velocity low pressure air to low velocitywith high pressure. The compressor manifold

diverts the flow of air from the diffuser,an integral part of the manifold,combustion chambers. In this desmanifold has one outlet port fcombustion chamber.

The outlet ports arc bolted to aelbow on the manifold. The outlet portthat the same amount of air is deliverecombustion chamber.

The outlets are known by a varietybut, regardless of the terminology uelbows change the airflow from radialaxial How, and the diffusion prcompleted after the turn. Each elbowfrom two to four turning vanes to efperform the turning process and to rpressure losses by presenting a smoothsurface.

The impeller is usually fabricatforged aluminum alloy, heat-treated, mmd smoothed for minimum How restriturbulence. Some types of impellersfrom a single forging. In other types thvanes are separate 'icces.

Centrifugal compressors mayefficiencies of 80% to 84% at pressure2.5:1 to 4:1 and efficiencies of 76% tpressure ratios of 4: 1 to 10:1.

Advantages: rugged, simple inrelatively light in weight andhigh-pressure ratio per stage.

Disadvantages: large frontal areefficiency, and difficulty in using twostages due to air loss that will occurstages and seals.

AXIAL FLOW COMPRESSORSThere are two main types

compressors (fig. 2-5). One is the drumthe other is the disc type. The drum tconsists of rings that are flanged toagainst the other, wherein the entire


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niinnnnnDnanurm

B) DISK TYPE203.25:26

Figure 2-5. Compressor rotors.

may then be held together by through bolts.This type of construction is satisfactory forlow-speed compressors where centrifugal stressesare low.

The disc type rotor consists of a series ofdiscs machined from aluminum forgings, shrunkover a steel shaft, with rotor blades dovetailedinto the disc rims. Another method of rotorconstruction is to machine the discs and shaft

bolt steel stub shafts on the front and reaassembly for providing bearing support sand splines for joining the turbine shafdisc type rotors are used almost exclusivepresent-day high-speed engines and are treferred to in this manual.

The purpose of the axial compressosame as the centrifugal type, to take in aair and increase the velocity and pressudischarge the air through the diffuser icombustion chamber.

The two main elements of an axicompressor are the rotor and stator (fig. 2

The rotor has fixed blades which foair rearward much like an aircraft prBehind each rotor stage is a stator. Thedirects the air rearward to the next rotoEach consecutive pair of rotor and statorconsitutes a pressure stage.

219.66Figure 2-6. Stator and rotor components of


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The action of the rotor at each stageincreases compression of the air at each stageand accelerates it rearward. By virtue of thisincreased velocity, energy is transferred from thecompressor to the air in the form of velocityenergy. The stators at each stage act as diffuse rs,partially converting high velocity to pressure.

The number of stages required is determinedby the amount of air and total pressure riserequired. The greater the number of stages, thehigher the compression ratio. Most present dayengines have 8 to 16 stages, depending on airrequirements.

Construction

The rotor and stators are enclosed in thecompressor case. Present day engines use a casethat is horizontally divided into upper and lowerhalves. The halves are normally bolted togetherwith either dowel pins or fitted bolts located atvarious points to ensure proper alignment toeach other and in relation to other engineassemblies which bolt to either end of thecompressor case.

On some older design engines the case is aone-piece cylinder open on both ends. Theone-piece compressor case is simpler tomanufacture; however, any repair or detailedinspection of the compressor rotor is impossible.The engine must be removed and taken to ashop where it is disassembled for repair orinspection of the rotor or stators. On manyengines with the split case, either the upper orlower case can be removed with the engine inplace for maintenance and inspection.

The compressor case is usually made ofaluminum or steel. The material used willdepend on the engine manufacturer and theaccessories attached to the case. The compressorcase may have external connections made as partof the case. These connections are normally usedto bleed air during starting and acceleration or atlow-speed operation.

DRUM-TYPE CONSTRUCTION.-Thedrum-type rotor (fig. 2-5A) consists of rings that

are flanged to fit one against tthe entire assembly may thenby through bolts. The drum isits full length. The blades anlength from front to rear, ancase tapers accordingly.construction is satisfactorycompressors where centrifugal

DISC TYPE CONSTRdisc-type rotor (fig. 2-5B) consdiscs machined from aluminumover a steel shaft. Anotherconstruction is to machine thfrom a single aluminum forginsteel stub shafts on the frontassembly to provide bearingand splines for joining the tblades vary in length from edue to a progressive reductioworking space (drum to casingby the increase in the rotor ddisc-type rotors are used almostpresent-day, high-speed engines.

ROTOR BLADES.-Theusually made of stainless or sMethods of attaching the bladerims vary in different designcommonly fitted into discs by2-7A) or fir tree (fig. 2-7B)blades are then locked by meanpeening, lockwires, pins, or key

Compressor blade tipscutouts, which are referre"profiles." These profiles allowoccurs when rotor blades cowith the compressor or housinserious damage to the blade or

Some manufacturers use aa spacer for the stators andwhen the blade tips come inring.

Another method of prevrubbing while maintaining minto metal-spray the case an


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SQUEALER TIP

(A) BULB ROOT TYPE

B) FIR-TREE TYPE

Figure 2-7. Rotor blades.203.24

"squealer tips" on the blades and vanes (fig. 2-8)contact the sprayed material. The abrasiveaction of the blade tip prevents excessiverubbing while obtaining minimum clearance.

The primary causes of rubbing are anexcessively loose blade or a malfunction of a

BLADEPLATFORM

BLADESHANK

DOVETAILSERRATION

Figure 2-8. Blade with squealer tip.

compressor support bearing which allcompressor rotor to drop.

Large compressors have loose fittingon the first several stages which moveacceleration to minimize vibration whilethrough critical speed ranges. Once up tocentrifugal force locks the blades in pllittle or no movement occurs. Theremovement of the blades during rundownclean engine some of the blades maymuch as 1/4-inch radial movement, and yhear a tinkling sound during rundown.

Large compressor rotors, with long blthe first stage, have a piece made onto thcalled a midspan platform (fig. 2-9platform gives some radial support to theduring acceleration, which is needed becthe length and amount of movementblades.

STATORS. The stator vanesradially toward the rotor axis and fit clo

21


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STAGE 1 BLADESTAGE 11 THRU 13 SPOOL

AIR DUCT ASSEMBLYSTAGE 14 THRU 16 SPOOL

STAGE 16 BLADE

NO. 4R BEARINGROTATING AIRVENT SEAL

STAGE 1 DISK

MID SPANPLATFORM

STAGE STAGE 2 DISKASSEMBLY STAGE 10 DISKSTAGE 3 THRU 9 SPOOL STAGE I'l -12 HUBTIE CLAMP

SH

NO. 4R BEARINROTATING OUTEAIR-SEAL NUTNO. 4R BEARINROTATING AISEAL

STAGE 15-16 HUBTIE CLAMP

Figure 2-9. Compressor rotor, LM 2500 engine.

either side of each stage of the rotor. Thefunction of the stators is twofold. (1) Theyreceive air from the air inlet duct or from eachpreceding stage of the rotor and then deliver theair to the next stage or to combustors at aworkable velocity and pressure. (2) The statorsalso control the direction of air to each rotorstage to obtain the maximum possiblecompressor-blade efficiency. The stator vanesare usually made of steel with corrosion- anderosion-resistant qualities. Frequently, the vanesare shrouded by a band of suitable material tosimplify tfre fastening problem. The vanes arewelded into the shrouds, and the outer shroudsare secured to the inner wall of the compressorcase by radial retaining screws.Some manufacturers machine a slot in theouter shrouds and run a long, thin key thelength of the compressor case. The key is held inplace by retaining screws to prevent the statorsfrom turning within the case. This method isused when a one-piece compressor case is slidr/er the compressor and stator assembly.

Each pair of vanes in a stator acdiffuser. They utilize the divergent principoutlet of the vane area is larger than thThis diverging area takes the high-velow-pressure air from the preceding rotoconverts it to a low-velocity, high-pairflow and then directs it at the proper athe next rotor stage. The next rotor strestore the air velocity that was lost duepressure rise. The next stator will give apressure rise. This process continues fstage in the compressor.

A 1.2X-pressure rise is about as musingle stage can handle. Higher pressuresult in higher diffusion rates with exturning angles, which cause excessiinstability, hence low efficiency. Althopressure RATIO remains unchanged acrostage, the pressure RISE varies across eacThe following is an example. Acompressor has a pressure ratio at each s1.1 and an ambient inlet of 14.7. What


31/92

final pressure? What is the overall pressureratio?

STAGE 1 STAGE 2 STAGE 314.7 X 1.1 = 16.17 X 1.1 = 17.79 X 1.1STAGE 4 STAGE 5 STAGE 6= 19.57 X 1.1 = 21.52 X 1.1 = 23.67 X 1.1STAGE 7 STAGES STAGE 9

- 26.04X 1.1 = 28.65 X 1.1 = 31.51 X 1.1STAGE 10 STAGE 11 STAGE 12

-34.66 X 1.1 =38.13 X 1.1 = 41.94 X 1.1STAGE 13= 46.13 X 1.1 = 50.75

FINAL PRESSURE = 50.75 psiINITIAL PRESSURE = 14.7 psiCompression ratio - '"i/ 7 ~ 3.45: 1The pressure rise across the first stage is:

16.2 psi pressure at back of 1st stage-14.7 psi pressure at front of 1 st stage

1.5 psi pressure rise across 1st stage

Pressure rise across the last stage is:

50.75 pressure at back of 13th stage-46. 1 3 pressure at front of 13th stage4.62 pressure rise across 13th stage

The pressure ratio is the same for each stage, butthe pressure rise is greater at the last stage. Thevelocity and density have an effect on pressurerise through a compressor. Compression ratiowill increase or decrease with engine speed. Thecompressor inlet temperature will also have aneffect on pressure rise through the compressor.

Preceding the stators and the first stage ofthe compressor is a row of vanes known as IGV's(inlet guide vanes). The function of the IGV'svaries somewhat, depending on the size of theengine and the air-inlet construction. On smallerengines the air inlet is not totally in line with thefirst stage of the rotor. The IGV straightens theairflow and directs it to the first-stage rotor. On

large engines the IGV's are variable anwith the variable stators. The variable Ilarge engines directs the airflow at theangle to reduce drag on the first stageVariable IGV's achieve the same purpvariable stator vanes (VSV's).

Small and medium engines have stastators. On large engines the pitch of thon several stators can be changed. For ethe first 6 stators of a 16-stage rotorvariable such as those used in theElectric LM 2500 engine (fig. 2-10).

The variable stators are controlcompressor inlet temperature (CIT) andpower requirements. They are movmechanical linkages that are connectedfuel-control governor. Variable statorstwofold purpose. (1) They are positivarious angles depending on compressor sensure the proper angle of attack betwcompressor blades. Varying the blade angto maintain maximum compressor effover the operating speed range of theThis is important in variable speed enginas those used for main propulsion. (variable stators on large engines veliminate "compressor surge." Surge (firesults when the airflow stalls acrocompressor blades; that is, air is not smcompressed into the combustion andsection. Stalling may occur over a few ba section of some stages, and, if enoughinterrupted, pressure may surge backthe compressor. This occurrence can be mvery severe with possible damage to theresulting.

All of the air in the combustor thenused for combustion instead of only theair. Lack of cooling air may cause etemperatures which burn the combustturbine section. (By a change in the anglstators and the use of bleed valves, thethrough the compressor is ensurecompressor surge can be almostprevented.)

Constant-speed engines, such as thoto drive generators, normally do not use

23


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STAGE 13 MANIFOLDSTAGE 9 MANIFOLD

STAGE 8 MANIFOLD

\

LEGEND:1. VANE SHROUD BUSHING (IGV, I & 2)2. FLANGED BUSHING3. WASHER4. SPACER (COLOR CODED)5. LEVER ARM6. SLEEVE7. LOCKNUT8. SLEEVE

9. ACTUATION RING SEGMENT10. ACTUATION RING SPACER11. LINE-UP PIN12. CONNECTING LINK13. ACTUATION LEVER MOUNT14. ROD END AND BEARING15. PUSH ROD16. ACTUATION LEVER CLEVIS

17. ACTUATION LEVER GUIDE18. ACTUATOR AND GUIDE BRACKET19. FEEDBACK BELLCRANK20. FEEDBACK BELLCRANK BRACKET21. VANE ACTUATION LEVER22. SELF ALIGNING BEARINGS23. SHOULDER BOLT24. SPACER

Figure 2-10. Compressor stator, LM 2500 engine.


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Chapter 2-ENGINE TYPES AND CONSTRUCTIONCOMBUSTION

Figure 2-11. Compressor surge. 277.16

stators because they are designed to operat100% rpm all the time. The proper fuel scheand air bleed valves are adequate to prevenminimize compressor surge.

DIFFUSER. -The diffuser (fig. 2- 12) plavery important role in the constructionoperation of a gas turbine. The diffuselocated between the compressor and

COMPRESSORDISCHARGER

COMPRESSORDISCHARGER

SHAFT BEARINGHOUSING-

DIFFUSOR

DIFFUSER ASSEMBLY


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INTRODUCTION TO MARINE GAS TURBINEScombustion chamber and, on some engines, itacts as a support for the rear compressorbearing. It also provides a means of support tothe inner and outer combustion liners. Thecombustor case may be bolted to one end of thediffuser along with the rear end of thecompressor case.

The struts of the diffuser may be cast withpassages through which (1) various bearings are

lubricated, (2) the bearing sump is scavand (3) the bearing cavity is vented eithersump, to an air-oil separator, or tatmosphere. On large engines the comprear frame along with the cowl asperforms the same functions as the dassembly in a small engine. (See fig. 2-2-14.)

The diffuser section operates on BernTheorem using the covergent-divergent pri

CDP LEAKAGETO AMBIENT

CUSTOMERBLEED

CUSTOMERBLEEDSCAVENGECDP LEAKAGETO AMBIENT

,,,.. n wrKi TMP VENTEMPTY

STRUT POSITIONSVIEW FROM AFTLOOKING FORWARD

CUSTOMERBLEED

'CDP LEAKAGE (TO TMF)CDP CAVITY DRAINLEAKAGE(TO TMF)OIL IN

I CASE

CDP AIR EXTRACTION HOLES(CUSTOMER BLEED)

AFT SEALPRESSURIZINGAIR HOLESSUMP HOUSING

AFT FLANGE

(STRUT NO. 8)CUSTOMER BLEEDPORT

MID FLANGEFUEL NOZZLE PAD

COMBUSTORMOUNTING PIN BOSS


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OUTER COWLFUEL NOZZLE EYELET

OUTER SKIRT

SEAL

COWLASSEMBLY

MOUNTINGPINBUSHING

DIFFUSERBOXFUEL NOZZLEFERRULE

277.19Figure 2-14. Combustor.

The diffuser takes the discharge of compressorair, straightens the flow of air, and distributes itevenly to the combustor for uniformcombustion and even temperatures throughoutthe combustor. The area across the diffuser is adiverging area. That is, the aft end of thediffuser is larger than the forward end. Due tothe increase in area there is a decrease in velocitywith an increase in volume at a constant pressureand temperature (Boyle's Law and Charles'Law). There is also an increase in static pressurewithin the combustor.COMBUSTION CHAMBERS. -The

combustion chambers have presented one of thebiggest problems in gas turbines. The extremestresses and temperatures encountered are notexperienced in other types ofinternal-combustion engines. The liners aresubjected to temperatures that range fromambient to as high as 4,000 F in a matter ofseconds.

The combustion chamber must have thecapability to operate over a wide range ofoperating conditions, to withstand a high rate of

burning, to have a minimum pressure drolight in weight, and to have minimum bul

The two common materials ucombustion chambers are Inconel for thor flame tubes and stabilized stainlesscombustor case.

The inner and outer liners or shroperforated with many holes and slotstheir length. Air is admitted through thefor combustion to protect the liner andthe gases at the chamber outlet The dethe flame tube is very critical to theefficiency of the engine.

The combustion chamber must ensuthe combustion process is completevariety of ranges. Poor design canflameouts, unburned fuel, or stratifiedreach the turbine section which can roverheating and damage to the turbine

There are two types of flow passagescombustion chambers the counterfloand through-flow path. The counterflowis rarely found in modern engines but wprimarily with very early design engines,the Whittle engine. The through-flowused in practically all modern engines.through-flow path the gases pass throucombustion section without a chadirection.

There are three types of combchambers: (1) can type, (2) annular typ(3) can-annular type. The can-type chaused primarily on engines that have a centcompressor. The annular and can-annuused on axial flow compressors.

Can-Type Chamber. The cacombustion system consists of individuaand cases mounted around the axisengine. Each chamber (fig. 2-15) containnozzle. This arrangement makes remochamber easy; however, it is aarrangement and makes for a structurallengine. The outer casing is welded to a rdirects the gases into the turbine nozzle. Ethe casings is linked to the others with


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TURNING VANESHEAD OF LINERSECONDARY AIR

COMPRESSORDISCHARGE

COMBUSTIONCHAMBERHOUSINGCOMBUSTIONCHAMBERLINER

COMBUSTIONCHAMBERCOVERCOMBUSTIONCHAMBERINLET DUCT

147.Figure 2-15. Elements of tubular or can-type combustion chamber.

tube which ensures that combustion occurs in allof the burners during light off. Inside each ofthese tubes is a flame tube that joins an adjacentinner liner.

Annular Chamber. The annular combustionchamber is usually found on axial flow engines.It is probably one of the most popularcombustion systems in use. The constructionconsists of a housing and liner the same as thecan-type.

attached at the turbine section and dsection.

The chamber may contain one orliners, one outside the other in the sameplane, hence the double-annular combchamber (fig. 2-16).

The dome of the liner has small slholes to admit primary air and to imswirling motion for better atomizationThere are also holes in the dome for t


37/92

Figure 2-16. Double-annular combustion chamber.

combustor case, and the inner liner preventsflame from contacting the turbine shaft housing.Large holes and slots are located along the

liners (1) to admit some cooling air into thecombustion space towards the rear of the spaceto help cool the hot gases to a safe level, (2) tocenter the flame, and (3) to admit the balance ofair for combustion. The gases are cooled enoughto prevent warpage of the liners.

The space between the liners and the caseand shaft housing form the path for secondaryair. The secondary air provides film cooling ofthe liners and the combustor case and shafthousing. At the end of the combustion spaceand just prior to the first-stage turbine nozzle,the secondary air is mixed with the combustiongases to cool the temperature to prevent warpingand melting of the turbine section.

The annular-type combustion chambvery efficient system that minimizes bucan be used most effectively in limitedThere are some disadvantages, howevesome engines, the liners are one-piecannot be removed without engine disasAlso, engines that utilize a one-piece comdome must be disassembled to remodome.

Can-Annular Chamber. The can-combustion chamber combines somefeatures of both the can and theburners.

The can-annular chamber design is a rthe split-spool compressor concept. Becathe problems encountered with a long shwith one shaft within the other, a dichamber was designed to fill a shorter spstill perform all the necessary functions.

29


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FUELNOZZLECLUSTERSPARK IGNITER

203.32Figure 2-17. Can-annular combustion chamber compo-

nents and arrangement.

Individual cans are placed inside an annularcase. The cans are essentially individualcombustion chambers (fig. 2-17) with concentricrings of perforated holes to admit air forcooling. On some models each can has a roundperforated tube which runs down the middle ofthe can. The tube carries additional air whichenters the can through the perforations toprovide more air for combustion and cooling.The effect is to permit more burning per inch ofcan length than could otherwise beaccomplished.

Fuel nozzle arrangement varies from onenozzle in each can to several nozzles around theperimeter of each can.

The cans have an inherent resistance tobuckling because of their small diameter. Eachcan has two holes which are opposite each othernear the forward end of the can. One hole has acollar called a flame tube. When the cans areassembled in the annular case, these holes andtheir collars form open tubes between adjacentcans so that a flame passes from one can to the

The short length of the can-annular chprovides minimal pressure drop of thebetween the compressor outlet and thearea. Another feature of the can-annularis the greater structural strength it gets frshort combustor area. Maintenance is sJust slide the case back and remove anburner for inspection or repair, rather thentire assembly. Another advantage is threlatively cool air in the annular outer canto reduce the high temperatures of thecans. At the same time, this air blanketthe outer shell of the combustion section

NOZZLES (TURBINE).-The stator eof the turbine section is known by a varnames of which the three most commoturbine nozzle vanes, turbine guide vanenozzle diaphragm. In this text, turbineare usually referred to as nozzles. The tnozzle vanes are located directly aftcombustion chambers and immediately fof, and between the turbine wheels.

Turbine nozzles have a two-fold fuFirst, after the combustion chambeintroduced the heat energy into the massand delivered it evenly to the nozzlenozzles prepare the mass flow for harnespower through the turbine rotor. The stablades or vanes of the turbine nozzlcontoured and set at such an angle thaform a number of small nozzles which dithe gas as extremely high-speed jets; thnozzle converts a varying portion of thand pressure energy to velocity energycan then be converted to mechanicalthrough the rotor blades.

The second purpose of the turbine nto deflect the gases to a specific angledirection of turbine wheel rotation. Sigas flow from the nozzle must enter theblade passageway while it is still rotatinessential to aim the gas in the general diof turbine rotation.

The elements of the turbine nozzle asconsists of an inner shroud and an outerbetween which are fixed the nozzle vanefiiin-i1- ai- r f wot-iao 1711-100 xi i+Vi A i ffe> ron f i"


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sizes of engines. Figure 2-18 illustrates typicalturbine nozzles featuring loose and welded vanefits.

The blades or vanes of the turbine nozzlemay be assembled between the outer and innershrouds or rings in a variety of ways. Althoughthe actual elements may vary slightly in theirconfiguration and construction features, there, isone characteristic peculiar to all turbine nozzles;that is, the nozzle vanes must be constructed toallow for thermal expansion. Otherwise, therewill be severe distortion or warping of the metalcomponents because of rapid temperaturevariances.

Thermal expansion of turbine nozzles isaccomplished by one of several methods. In onemethod the vanes are assembled loosely in thesupporting inner and outer shrouds (fig. 2- ISA).Each of the vanes fits into a contoured slot inthe shrouds which conform with the airfoilshape of the vanes. These slots are slightly largerthan the vane to give a loose fit. For furthersupport the inner and outer shrouds are encasedby an inner and an outer support ring which addstrength and rigidity. These supports also permitremoval of the nozzle vanes as a unit; otherwise,the vanes could fall out of the shrouds as theshrouds are removed.

Another method to allow for thermalexpansion is to fit the vanes into inner and outershrouds. In this method the vanes are welded orriveted into position (fig. 2-18B). To provide forthe inevitable thermal expansion, either theinner or the outer shroud ring is cut intosegments. The saw cuts dividing the segmentswill allow sufficient expansion to prevent stressand warping of the vanes.

The basic types of construction of nozzlesare the same for all types of turbines. Theconvergent-divergent principle (Bernoulli'sprinciple) is used to increase gas velocity.

The turbine nozzles are made ofhigh-strength steel to withstand the directimpact of the hot, high-pressure, high-velocitygases from the combustor. The nozzle vanesmust also resist erosion from the high-velocitygases passing over them.

CA)

CB)

Figure 2-18.-(A) Turbine nozzle vane assembloose fitting vanes; (B) Turbine nozzle vane awith welded vanes.

Increasing the inlet temperature of thby approximately 750F makes it possachieve an approximate 100% increspecific horsepower. However, nozzlesstand up for long to the higher temperDifferent methods of increasingendurance have been tried over the years.

One method that was tried was to cnozzle with a ceramic coating.temperatures were achieved, but the diexpansion rates of the the steel and the ccaused the coating to break away over aof time. Experiments are still being condeven so far as to use an entirely ceramic

Another means of withstandingtemperatures is to use space-ageHowever, extreme costs of the metals pcommercial production of such nozzles.

i

Still another method, which is in witoday in large engines, is to use air-cooled

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INTRODUCTION TO MARINE GAS TURBINESblades. Compressor bleed air is fed throughpassages to the turbine where it is directed tothe nozzle. The air cools both the turbine(discussed later) and the nozzle. The nozzle mayalso be cooled by air admitted from the outerperimeter of the nozzle ring. The method ofgetting the air in is determined by themanufacturer.

The nozzle vanes are made with many smallholes or slots on the leading and trailing edges(fig. 2-19). Air is forced into the nozzle and outthrough the slots and holes, cooling the vane asit passes through. The air is discharged into thehot gas stream, passing through the remainder ofthe turbine section, and then out the exhaustduct.

Figure 2-20 compares temperature of anair-cooled vane against a nonair-cooled vane.

Cooling air is used primarily in the H.P.turbine section. The temperature of the gases is

at an acceptable level by the timethe L.P. turbine section where meusage will last for long periods of t

Seals installed between the nshroud and the turbine shaft maywith bleed air to minimize interstthe gases as they pass through theTHE TURBINE ASSEMBLY

In theory, design, ancharacteristics, the turbines usedengines are quite similar to the tursteam plant. The gas turbine disteam turbine chiefly in (1) the tmaterial used, (2) the meanscooling the turbine shaft bearinglower ratio of blade length to whee

The terms gas generator turbturbine are used to differentiateturbines. The gas generator turbigas generator and accessories. Thepowers the screw through the redushafting.

INSERT COVER-

TRAILINGEDGESLOTS

16TH-STAGEAIR IN

-NOSE HOLES

STAGE 1 16TA

Fi ure 2-19. First-sta e as enerator turbine nozzle coolina.


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NONAIR COOLED1900

GASES 18501800

ROOT 1750

SHAFT

AIR COOLED1600 C

AIRFOIL

1350} FIR TREE 1300 C

DISK RIM 1250DISK 1225HUB 1200

Figure 2-20. Cooling comparisons between an air-cooled vane and a nonair-cooied vane.

The turbine which drives the compressor ofa gas turbine engine is located directly behindthe combustion chamber outlet. The turbineconsists of two basic elements, the stator ornozzle, and the rotor. Part of a stator element isshown in figure 2-21; a rotor element is shownin figure 2-22.The rotor element of the turbine consists ofa shaft and bladed wheel(s). The wheel(s) areattached to the main power transmitting shaft ofthe gas turbine engine. The jets of combustiongas leaving the vanes of the stator element actupon the turbine blades and cause the turbinewheel to rotate in a speed range ofapproximately 3,600 to 42,000 rpm. The highrotational speed imposes severe centrifugal loadson the turbine wheel, and at the same time thehigh temperature (1,050 to 2,300 F) results ina lowering of the strength of the material.Consequently, the engine speed and temperaturemust be controlled to keep turbine operationwithin safe limits. The operating life of theturbine blading usually determines the life of thegas turbine engine.The turbine wheel is a dynamically balancedunit consistin of blades attached to a rotatine

disk. The disk in turn is attached to thshaft of the engine. The high-velocitygases leaving the turbine nozzle vanes actblades of the turbine wheel, causiassembly to rotate at a very high rate of

The turbine disk is referred to as sucin an unbladed form. When the turbineare installed, the disk then becomes thewheel. The disk acts as an anchoring comfor the turbine blades. Since the disk is bowelded to the shaft, it enables the blatransmit to the rotor shaft the energextract from the exhaust gases.

The disk rim is exposed to the hopassing through the blades andconsiderable heat from these gases. In adthe rim also absorbs heat from theblades by conduction. Hence, distemperatures normally are quite high anabove the temperatures of the moreinner portion of the disk. As a result otemperature gradients, thermal stressadded to the stresses caused by rotation.

Various means are provided to relileast artiall the aforementioned stresse.


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147.144Figure 2-21. Stator element of turbine assembly.

such means is the_ incorporation of an auxiliaryfan somewhere ahead of the disk, usually rotorshaft-driven, which forces cooling air back intothe face of the disk.

Another method of relieving the thermalstresses of the disk follows as incidental to bladeinstallation. By notching the disk rims toconform with j blade root design, the disk ismade adaptable for retaining the turbine blades,and at the same time space is provided by thenotches for thermal expansion of the disk.The turbine shaft is usually fabricated fromlow-alloy steel. It must be capable of absorbing

1Figure 2-22. Rotor element of turbine assem

high torque loads, such as exerted whenaxial flow compressor is started.

The methods of connecting the shaftturbine disk vary. One method used is wThe shaft is welded to the disk, which haor protrusion provided for the joint. Amethod is by bolting. This method requithe shaft have a hub which matches a masurface on the disk face. The bolts tinserted through holes in the shaft hanchored in tapped holes in the disk. Ofmethods the latter is more common.

The turbine shaft must have some mejoining the compressor rotor hub; this isaccomplished by making a splined cutforward end of the shaft. The spline fitcoupling device between the compressorturbine shafts. If a coupling is not ussplined end of the turbine shaft may fisplined recess in the compressor rotor hucentrifugal compressor engines use thecoupling arrangement almost exclusivelyaxial compressor engines may use eitherdescribed methods.

There are various ways of attachingblades. Some ways are similar to t


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Chapter 2-ENGINE TYPES AND CONSTRUCTIONcompressor blades are attached. The mostsatisfactory method used is the fir-tree designshown in figure 2-23.

The blades are retained in their respectivegrooves by a variety of methods. Some of themore common methods are peening, welding,locking tabs and riveting. Figure 2-24 shows atypical turbine wheel utilizing riveting for bladeretention.

The peening method of blade retention isused quite frequently, and its use may beapplied in various ways. Two of the mostcommon applications of peening are described inthe following paragraphs.

One peening method requires you to grind asmall notch in the edge of the blade fir-tree rootprior to installing the blade. After you haveinstalled the blade in the disk, the notch will fillwith the disk metal, which is "flowed" into itthrough a small punchmark which you make inthe disk adjacent to the notch. The tool you usefor this job is similar to a centerpunch and isusually manufactured locally.

Another peening method is to construct theroot of the blade in such a way that it containsall the elements necessary for its retention. Thismethod, illustrated in figure 2-25, shows thatthe blade root has a stop made on one end ofthe root so that the blade may be inserted andremoved in one direction only, while on theopposite end is a tang. You peen this tang overto secure the blade in the disk.

Turbine blades may be either forged or cast,depending on the metal they are made of.

Turbine blades are usually machined fromindividual forgings. Various materials are used inthe forging. Speed and operating temperaturesare important factors that decide whichmaterials go into the turbine blades.

Large engines utilize an air-cooled bladingarrangement on the gas generator turbine. (Seefig. 2-26.) Compressor discharge air iscontinuously fed through passages along the

Figure 2-23. Turbine blade with fir-tree designlock method of blade retention.


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STOP LOCATESAGAINST WHEEL

TANGIS PEENED

OVER TO SECURE

203.39Figure 2-25. Turbine bucket, featuring peening method

of blade retention.

second-stage turbine wheels dirair along the face of the disk fodisk. The air is then directed thrfir-tree portion of the disk, iblade fir-tree, and up through hoto cool the blades. (See figure 2-

Cooling of the turbine whreduces thermal stresses onmembers. The turbine nozair-cooled. By cooling therotating parts of the turbineturbine inlet temperatures are pallow for more power, a moreand longer engine life.

POWER TURBINESTurbine wheels are used

ways.1. The aircraft jet turbine

turbine extracts only enoughgases to run the compressor and2. In the solid-wheel tur

turboprop airplane or ship'sengine, as much energy as poss

THESH

LABYRINTHSEALS

Figure 2-26. Gas generator turbine rotor cooling.

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SQUEALER TIP

LEADING BLADE AIRFOIL AIRINLET HOLES TRAILING BLADESTAGE 1

SQUEALER TIP

BLADEPLATFORM

BLADESHANK 4-

DOVETAIL-SERRATIONS

r~-*-~r J.=&J._^J \

LEADING BLADE AIRFOIL AIRINLET HOLESSTAGE 2

MATINGSURFACE

TRAILING BLADE-

Figure 2-27. Gas generator turbine rotor blade cooling.

from the gases to turn the turbine whichprovides power for the compressor, accessories,and the airplane propeller or the ship'sgenerator. These engines are designed to run at100% specified rpm all the time. The location ofthe mechanical connection between the turbinewheel and the reduction gear on the compressorfront shaft depends on the design of the

installation. Normally, there is no medisconnect a ship's service generator fromturbine except by disassembly. This sused for generators since there canslippage between the engine and the gen

3. Currently used Marine propengines use a combination of the two

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stage high-pressure rotor that drives thecompressor and accessories.

The power turbine (fig. 2-28) is a multistageturbine located behind the gas generator turbine.There is no mechanical connection between thetwo turbines. The power turbine is connected toa reduction gear through a clutch mechanism.

a reverse gear is used to changevessel.

Some ships that have two scountcrrotating power turbiturbines on one shaftwhile the turbines on tcounterclockwise. This arran

FRONT SHAFT

SHROUD ANDNOZZLE INSULATORS

NO. 6BEARINGAIR SEALHORIZONTAL FLANSE

TURBINE CASINGNOZZLES

PRESSUREBALANCE SEALINTERSTAGESEALS

EXTENDED HONEYCOMB

STAGE-ROTOR

NOZZLE LOCKS

FRONTFLANGE REAR FLANGE

CASTING BODY

Figure 2-28. Power turbine.

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the use of a V-drive. The gas generator portionrotates in the same direction for both sets ofengines. Directional rotation of the powerturbine is determined by the blade angle of thewheel and the nozzles in the power turbinesection. On large ships where different lengthpropeller shafts are permitted, the engine(s) canbe mounted to the other end of the reduction-gear to achieve counter-rotation of the screw.

By varying the gas generator speed, theoutput speed of the power turbine can becontrolled. Since only a portion of the energy isused to drive the compressor, the plant can beoperated very efficiently. For example, on acold day it is possible to have 100% powerturbine specified rpm with 80% to 90% gasgenerator specified rpm. The variables discussedearlier in the chapter account for this situation.

The power turbine is constructed much likethe gas generator turbine. The most noticeabledifferences are (1) the absence of cooling air,and (2) the power turbine blades haveinterlocking shroud tips for low vibration levels.Honeycomb shrouds in the turbine case matewith the blade shrouds to provide a gas seal andto protect the case from the high-temperaturegas. Two popular methods of blade retention arethe bulb-type and the dovetail.

MAIN BEARINGSThe main bearings have the critical function

of supporting the main engine rotor. For themost part, the number of bearings necessary forproper engine support is decided by the lengthand weight of the engine rotor. The length andweight are directly affected by the typecompressor used in the engine. Naturally, asplit-spool axial compressor will require moresupport than a simple centrifugal compressorengine. The minimum number of bearingsrequired will be three, while some of the latermodels of split-spool axial compressor engineswill require six or more.The gas turbine rotors are usually supportedby either ball or roller bearings, but someengines use sleeve bearings. Hydrodynamic orslipper-type bearings are receiving some

attention for use on turbine powerplantsoperating rotor speeds approach 45,000 rwhere excessive bearing loads during opeare anticipated. (See fig. 2-29). In generaor roller antifriction bearings are prlargely because they offer little rotresistance; facilitate precision alignmerotating elements; are relatively inexpmay be easily replaced; can withstandmomentary overloads; are simple tolubricate, and maintain; can accomodatradial and axial loads; and are relatively reto elevated temperatures. Thedisadvantages are their vulnerability tomatter damage and their tendencywithout appreciable warning.

Usually, the ball bearings are positiothe compressor or turbine shaft so thamay absorb any axial (thrust) loads orloads. The roller bearings are better equipsupport radial loads than thrust loads bthey present a larger working surface. Thethey are used primarily for this purpose.

The elements of a typical ball orbearing assembly include a bearing shousing, which must be strongly consand supported to carry the radial and axiaof the rapidly rotating rotor. Thehousing usually contains oil seals to prevoil's leaking from its normal path of flow,also delivers lubricating oil to the busually through spray nozzles.

On modern engines, the bearing is moin a sump. The bearing sump has a lirie twhich the lube oil is scavenged backsump. The bearing sump is also venprevent either a pressure or vacuum. Thgoes either to the atmosphere or to anseparator.

OIL SEALS

The three types of oil seals that are cin gas turbines are: (1) lip-type sealabyrinth/windback, and (3) carbon ring.

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NO. 4R BEARINGSTATIONARY OIL SEAL

CARBON SEALCARBONSEALMATINGRING

0-RINGGROOVE

CUSEASUR

ANTI- ROTATIONTANG CARBON ELEMENSEALING SURFACCARBON RING SEAL

SEALSURFACEWINDBACK THREADS

SERRATIONS

OILSLINGER

LABYRINTH / WINDBACK SEAL

N0.4R BEARINGROTATING OIL S

Figure 2-31. Typical oil seals.

amount of seal pressurization air to leak into thesump, thereby preventing oil leakage.CARBON RING SEAL

The carbon seal consists of a stationaryspring-loaded, carbon sealing ring and a rotating,highly polished steel mating ring. It prevents oilin the gearbox from leaking past the drive shaftsof the starter, fuel pump, and auxiliary drivepad.Another form of the carbon seal is also inuse. The carbon rings are not spring-loaded.

They move freely around the shaft aaxially against their housing. When the eup to speed, the rings center themselvesin the housing. Compressor bleed air is fobetween the carbon rings. The air presforced out along the shaft in both dirThe pressure prevents oil from entericompressor or turbine and combustiofrom reaching the bearings. Thedisadvantage of this type seal is minleakage during start up and run down aspump moves oil before there is sufficient

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CHAPTER 3STARTING SYSTEMS

Gas turbine engines are started by turningthe compressor at sufficient speed to initiate andsustain combustion. Both the compressor andthe compressor turbine must be spun. In startingdual axial-flow compressor engines, thehigh-pressure compressor is the only one thestarter needs to rotate. The starter's firstrequirement is to accelerate the compressor toprovide sufficient airflow and pressure tosupport combustion in the burners.

Once fuel has been introduced and th

Documents

Introduction to Marine Gas Turbines