gas turbine theory mjh

8/8/2019 Gas Turbine Theory Mjh

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Gas Turbine TheoryGas Turbine Theoryand Constructionand Construction


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Introduction

Introduction

Comprehend the thermodynamicprocesses occurring in a gas turbineComprehend the basic components of gasturbine engines and their basic operationComprehend the support systemsassociated with gas turbine engines


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Background

BackgroundAircraft turbojet/turbofan engines are precursors

to gas turbinesInstalled for propulsion in:

FFGsDDsDDGsCGs

M-1 tanksAlso used for electrical generation & auxiliaryapplications


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Advantages of GTEsAdvantages of GTEsWeight reduction of 70%SimplicityReduced manning requirements

Quicker response timeFaster Acceleration/decelerationModular replacementLess vibrationsMore economical


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Disadvantages of GTEs

Disadvantages of GTEs

Many parts under high stressHigh pitched noiseNeeds large quantities of airLarge quantities of hot exhaust (target)

Cannot be repaired in place


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Brayton CycleBrayton CycleUnlike diesels, operate on STEADY-FLOW cycleOpen cycle, unheated engine

1-2: Compression

2-3: Combustion

3-4: Expansion throughTurbine and Exhaust

Nozzle

(4-1: Atmospheric

Pressure)


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Basic ComponentsBasic Components


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Basic ComponentsBasic Components


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Basic ComponentsBasic ComponentsCompressorCompressor

Draws in air & compresses itCombustion Chamber

Fuel pumped in and ignited to burn with compressed

airTurbineHot gases converted to workCan drive compressor & external load


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Basic ComponentsBasic ComponentsCompressor

Draws in air & compresses itCombustion ChamberCombustion Chamber


airTurbineHot gases converted to workCan drive compressor & external load


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Basic ComponentsBasic ComponentsCompressor

Draws in air & compresses itCombustion Chamber


airTurbineTurbineHot gases converted to workCan drive compressor & external load


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CompressorCompressorSupplies high pressure air for combustionprocessCompressor types

Radial/centrifugal flow compressorAxial flow compressor


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CompressorCompressorRadial/centrifugal flow

Adv: simple design, good for low compression

ratios (5:1)Disadv: Difficult to stage,less efficient

Axial flowGood for highcompression ratios (20:1)Most commonly used


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CompressorCompressor

Controlling Load on CompressorTo ensure maximum efficiency and allow forflexibility, compressor can be split into HP &LP sectionsVane control: inlet vanes/nozzle angles can be

varied to control air flowCompressor StallInterruption of air flow due to turbulence


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Use of Compressed AirUse of Compressed Air

Primary Air (30%)Passes directly to combustor for combustionprocess

Secondary Air (65%)Passes through holes in perforated inner shell& mixes with combustion gases

Film Cooling Air (5%)Insulates/cools turbine blades


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Combustion ChambersCombustion Chambers

Where air & fuel are mixed, ignited, and burned Spark plugs used to ignite fuelTypes

Can: for small, centrifugal compressors

Annular: for larger, axial compressors (LM2500)Can-annular: for really large turbines


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TurbinesTurbinesConsists of one or more stages designed todevelop rotational energy

Uses sets of nozzles & blades


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TurbinesTurbinesSplit Shaft

Gas generator turbine drives compressorPower turbine separate from gas generator turbinePower turbine driven by exhaust from gas generator

turbinePower turbine drives power coupling


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Single ShaftSingle Shaft

Efficiently operates at constant speedsUsed in GTGS (gas turbine generator systems)Single shaft

Power coupling on same shaft as turbineSame shaft drives rotor of compressor and powercomponents

*Primarily used for electric power because of constant speed, regardless of load.


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Split ShaftSplit Shaft

Best where speeds and loads varyUsed in LM-2500

Power shaft is decoupled from compressorAllows both to operate at efficient speeds (notthe same)

*More suitable for main propulsion applicationsdue to the fact that the gas generator turbine and power turbine operate near their most efficientspeeds throughout a RANGE of load demands.


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Accessory

Drive

Assembly

Accessory

Drive

Assembly

Purpose - Provides motive force for driving

the accessories required for operation and control of engineAttached Accessory Equipment

Fuel oil pumpLube oil pumpStarter (pneumatic, electric, hydraulic)


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Gas Turbine SystemsGas Turbine Systems

Air SystemAir intakes are located high up & multiplefiltersExhaust discharged out stacks

Fuel SystemUses either DFM or JP-5

Lubrication SystemSupply bearings and gears with oil


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Q uestions?Q uestions?

gas turbine theory mjh

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