Introduction to Gas Turbine Engines

Home , Turboprop, Turboshaft

Introduction

• Gas Turbine Engine - Configurations

Gas Generator

Compressor is driven Turbine is driven by the turbine through by heated air an interconnecting from the shaft combustor

T u r b Compressor Combustor i n e

Gas Generator – Heart of Gas Turbine (to supply high-temperature and high-pressure gas to the turbine)

Adapted: “Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly

Turbojet

Exhaust

Schematic of a Twin Spool Turbojet

Adapted: “Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly

Schematic of Turbojet with Afterburner

Afterburning Turbojet (Concorde)

• Additional turbine stages may be added to extract more gas energy into mechanical power – Less residual exhaust energy – Reduced thrust generated by core engine • Mechanical power directed to drive: – Shrouded fan >>> Turbofan – Propeller >>> Turboprop – Rotor blades >>> Turboshaft

Turbofan

1. Nacelle 2. Fan 3. Low pressure compressor 4. High pressure compressor 5. Combustion chamber 6. High pressure turbine 7. Low pressure turbine 8. Core nozzle

Source: http://en.wikipedia.org/wiki/Turbofan

Turbofans offer: • High efficiencies • Reduced noise levels

Bypass ratio ~ 9.3

F15, F16 P&W F100 Engine

Bypass ratio ~ 0.36

Source: http://en.wikipedia.org/wiki/Pratt_%26_Whitney_F100

Schematic of Unmixed Turbofan (Twin Spool)

Adapted: “Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly

Turbofan Station Numbering

Schematic of Unmixed Turbofan (Twin Spool)

Adapted: “Elements of Propulsion: Gas Turbines and Rockets” by Jack D. Mattingly

• Turbine, through reduction gear box, drives – A propeller - turboprop engine – Rotor blades – turboshaft engine (helicopters) • Exhaust gas is not a significant contributor to aircraft thrust • Power to drive the reduction gearbox can be extracted either from – the same turbine that drives the compressor or – from a separate, free-wheeling turbine (Power Turbine)

Schematic of Turboprop

Turboprop & Turboshaft

Schematic of Turboshaft with Power Shaft Driven by Free Power Turbine

Source: http://en.wikipedia.org/wiki/Turboshaft

• Propeller typically kept at constant rotational speed (rpm) • Propeller blade angle variable and controllable according to speed demands • Blade angle can be set to: – reverse pitch for reverse thrust – “Feather” to stop engine rotation

Photo credit: Soon Kim Tat

Turboprop

• Advantages and limitations of the turboprop are those of the propeller: – Excellent performance for low-speed flight and short-field take-off – High propulsive efficiency and high thrust at low subsonic speeds – Approaching the speed of sound, the propeller/rotor loses its aerodynamic efficiency due to compressibility effects

Photo credit: Soon Kim Tat

Watch video of C130 Turboprop take-off: http://www.youtube.com/watch?v=nwaWXrlZEIw

• Rotors kept at constant rpm • Rotor blade angle variable and controllable according to demands for lift (collective pitch), or speed and banking (cyclic pitch)

Photo credit: Soon Kim Tat See video on how collective and cyclic pitch control works: http://www.youtube.com/watch?gl=SG&hl=en-GB&v=7HBziltI_t4

Ramjet

• Conceptually the simplest jet engine – Inlet – combustion chamber – nozzle • No rotating component • Compresses incoming air by decelerating it in the inlet Schematic of Ramjet • Requires forward motion to produce thrust Source: http://en.wikipedia.org/wiki/Ramjet

J58 Engine

Source: Rolls-Royce, 1986, The jet engine, 5 th edition, Rolls-Royce plc

SCRAMJET

• Supersonic Combustion RAMJET • Hypersonic flights (experimental)

Source: Wikipedia http://commons.wikimedia.org/wiki/File:Scramjet_operation.png

• The heart of the gas turbine engine – the gas generator • The different gas turbine configurations: – Turbojet (including with afterburner) – Turbofan or Bypass Engine – Turboprop and Turboshaft. • The operation of a Ramjet and Scramjet

Reflection Question

• Explain the construction of a turbofan engine and elaborate on its advantages compared to a turbojet.