2. Course Outline - First 02 weeks
• Gas turbine engine/ aircraft propulsion history , why gas turbines ???
• Gas turbine basics (thermodynamics)
• Working principle (Brayton cycle and control volume approach )
• Need of gas turbine testing and types
• Performance Parameters
• Calculation of Thrust , SFC and Specific Thrust !!!!!!
3. Reference Books
• Introduction to flight by John D Anderson Jr
• Gas Turbine Theory by HIH Saravanamutto, GFC Rogers, H Cohen, PV
Stranznicky, AC Nix
• Elements of Gas Turbine Propulsion by JD Mattingly
• Relevant Open Source Research papers on Engine Testing
• Engine Testing and Performance Evaluation Docket
4. Gas turbine history
• Principle of rocketry used more than 2000 yrs ago by Chinese
• The wooden pigeon of Archytas around 400 B.C
• Aeolipile- Radial steam turbine , Hero of Alexandria around 50 AD
• Real rockets by Chinese in first century AD for colour displays and religious festivals
5. Gas turbine history
• Sir Isaac Newton in the 18th century was the first to theorize that a rearward-channeled
explosion could propel a machine forward at a great rate of speed. This theory was based on
his third law of motion.
• Henri Giffard built an airship which was powered by the first aircraft engine, a three-horse
power steam engine. It was very heavy, too heavy to fly.
• In 1874, Felix de Temple, built a monoplane that flew just a short hop down a hill with the
help of a coal fired steam engine
• Otto Daimler in the late 1800's, invented the first gasoline engine.
• In 1903, the Wright Brothers, flew, "The Flyer", with a 12 horse power gas powered engine.
• From 1903, the year of the Wright Brothers first flight, to the late 1930s the gas powered
reciprocating internal-combustion engine with a propeller was the sole means used to propel
6. Gas turbine history
• Robert Goddard experimentally proved the first multistage rocket using liquid fuel 1920s
• Dr . Herman Oberth helped the Nazi’s to develop V2 rocket
• It was Frank Whittle, a British pilot, who designed the first turbo jet engine in 1930.The
first Whittle engine successfully flew in April, 1937. This engine featured a multistage
compressor, and a combustion chamber, a single stage turbine and a nozzle.
• The first jet airplane to successfully use this type of engine was the German Heinkel He
178 invented by Hans Von Ohain in 1939. It was the world's first turbojet powered flight.
10. Gas Turbine Basics
• The fundamental principles of all aerospace propulsion are “Newton’s Law of Motion”.
Newton’s second law : Force acting on a body is proportional to the rate of change of
momentum of that body. This force acts in the direction of increasing momentum
• Newton’s third law
Action and reaction are equal and opposite
• The basic principle is that a stream of air/gases is speeded up (work is done on the stream
of air/gases), and is ejected backwards (with higher velocity or momentum). Hence a
forward thrust is developed on the engine.
• The source of energy for the work done on the stream of air has to come from somewhere .
Fuels are burned and from this mechanical energy is derived . This is governed by the laws
11. Gas Turbine Basics
• Air inlet: captures air and delivers efficiently to the compressor
• Compressor: increases air pressure and temperature
• Combustor: increases temperature of incoming air by burning the mixture of air and
fuel (aviation kerosene). Fuel is supplied via the injection system
• Turbine: Extracts energy from the hot gases and runs the compressor
• Nozzle: Accelerates the gases further
12. Gas Turbine Basics
• Three important parameters and design factors
Pressure ratio, TIT, Component efficiencies
• Combustion at constant pressure and constant volume
• Open cycle and closed cycle arrangement
• Multi-spool arrangements. why ??
14. The Jet Propulsion Thrust Equation
• Fundamental mechanisms by which nature communicates a force to a solid surface -
surface pressure and shear stress distributions
• Same principles carry over to Jet Propulsion
15. The Jet Propulsion Thrust Equation
• Consider the volume of the gas bounded by the dash lines- control volume.
• Gas exerts Ps on the duct and the duct exerts an equal and opposite Ps on the edges of
the gas in the control volume. Pe is the static pressure at the exit of the duct.
17. Need for GT Engine Testing
• Designer design the engine with certain aims in mind
• To verify the designed and the developed engine , one has to go for testing
and performance evaluation of the engine
• GT testing is done
• To check if the engine is operating within the design parameters
• To check the structural integrity of the engine- mechanical strength
• To help the certification and validation team to qualify the engine for the operational
• To prove the ruggedness of the engine in adverse operating environments
18. Need for GT Engine Testing
• The various parameters tested are :
• Thrust , power , efficiency
• Operating lines and stall margins
• Fuel flow, SFC
• Engine air flow
• Bleed air flow
• Vibration levels
• Pressures and temperatures
• Rotor speeds
• Engine Pressure Ratio or EPR
19. Philosophy and Rationale of Testing
• Testing involves subjecting the engine to conditions experienced by an
actual , in service engine, in flight , and on ground.
• Tests are conducted to check how the engine responds to the situation
while also measuring the time for which it runs normally before deviating to
abnormal and potentially harmful behaviour
20. Types of Testing
• Endurance test
• Fan Blade off test
• Bird strike test
• Rain and hail ingestion test
21. Types of Testing
• Bird ingestion test
• 17,494 jet engines were struck in 16,694 bird strike events. Out of these, 4516
engines were damaged in 4370 bird strike events (4227 events with one engine
damaged, 141 with two engines damaged (such as the Hudson landing event), 1 with
three engines damaged, and 1 with four engines damaged
22. Types of Testing
• Bird ingestion test
• The FAA’s test for a bird strike during take-off requires that a bird is fired at the engine core at a
speed of 250kts, with the mechanical engine fan speed set at the lowest expected speed when
climbing through 3,000ft altitude above ground level (AGL). The engine would then be required
to run with no less than 50% take-off thrust allowed during the first minute after bird ingestion.
• If the engine passes that test with no parts of the bird entering the core, the manufacturer will
be required to perform a further test in which a bird is ingested at 200kts, with the engine set at
the lowest fan speed expected when descending through 3,000ft altitude AGL on approach to
landing. The engine should run for six minutes after the impact.
25. Types of Testing
• Altitude testing
• Icing test
• Strain gauge testing
• Low temperature starting test
• Cross wind test
• Water trough test
26. Types of Test Beds
• Outdoor sea level test bed
• It is situated in open air area. The stand basically consists of frame (cradle)
supporting an engine and providing the thrust measurements.
• The effects of cross wind on input air conditions are supressed by a large mesh
screen that is fitted around the engine inlet. The area surrounding the test bed is free
of the obstructions to the air flow, to ensure the validity of the thrust and the air flow
• This is the most precise thrust test bed, because in the indoor test beds the thrust and
the air flow measurements are negatively influenced by the effect of sidewalls on flow
• Due to the logistic difficulties and the impact of adverse weather conditions, indoor
testing is preferred in most cases, with the thrust measurements calibrated
(correlated) to the condition of outdoor facilities
28. Types of Test Beds
• Indoor sea level test beds
• It is enclosed by a building, called the test cell. The air flow path to the engine is
crucial, because it is highly restricted by available area.
• The disturbance must be known and minimised. It is necessary to compare indoor
measurement results with outdoor results of the same, or very similar engine. What is
“very similar” is stated using correlation tests in both facilities.
• The test cell equipment, called detuner, is the tubular outlet of the test section. Gas
from the engine output nozzle enters the detuner, which guides it out of the test cell
and provides sound attenuation.
• For a given engine, the measured thrust is decreased up to 10% in comparison with
the value recorded at outdoor test bed. This is due to unstable static pressure effects,
acting on the engine, its equipment and the cradle, caused by the air streaming within
• The indoor test cell gives useful all-weather availability.. it should be calibrated
against outdoor test bed, to determine the effects of the static pressure field
30. Types of Test Beds
• Flying test bed
• A flying test bed is used for testing of power unit in real condition. Usually a four
engine aircraft is adapted to mount a single, new development engine at one position.
• The advantages are better simulation of effects such as plane and structure loads and
inlet distortion, low budget.
• There are no direct measurements of the thrust and the mass flow. These must be
calculated as follows:-
• propelling nozzle thrust coefficient and capacity are obtained from rig and engine tests
• nozzle entry total pressure and temperature are measured directly, with sufficiently
covered sensors to obtain valid average data
• mass flow can be calculated using exit velocity
• fuel flow is measured
31. Types of Test Beds
• Flying test bed
• Flying test bed - Boeing 747-SP The engine under test can be installed on a special pylon
in front of the aircraft behind the pilots cabin
32. Engine Concept Design Process
• Engine concept design requires full understanding of the GT Performance
• Design process involves
• Statement of requirements
• First cut aero-thermal component design
• Design point calculations and aero thermal component design iterations
• Engine layout
• Off design performance
• Performance , aero thermal and mechanical design investigation
• Minimum engine
• Design and development programme shortfall
• Installation losses
• Formal Tests
37. Module 2
• Ideal cycle analysis
• Component analysis
• Real cycle analysis
• Calculation of performance parameters
38. Ideal cycle analysis
• It describes the thermodynamic changes of the working fluid as it flows
through the engines
• Determines the performance of the engines at different aircraft operating
• Relates engine performance parameters to
• Design choices (compressor pressure ratio, fan pressure ration)
• Design limitations (Compressor exit pressure , TIT)
• Flight conditions (Flight Mach number, ambient temperature etc )
44. Thrust augmentation
• Requirement of an additional thrust for a shorter period of time is essential during flight operation.
Typical cases are: take-off, acceleration from subsonic to supersonic speeds, combat operations,
etc. Thrust augmentation is adopted in aircraft engines totackle such cases.
• Two different methods are commonly used: Liquid injection and afterburning.
• Liquid injection: Spraying water into the compressor inlet causes a reduction in compressor inlet
temperature. This effect increases the compressor pressure ratio and thereby increases the thrust.
• Afterburning: The temperature of gas exiting from the turbine is increased by burning additional fuel
in a duct (jet pipe). This provide a larger jet exit velocity and thereby increases the thrust.
• Due to the absence any rotary components, the gas temperature can reach closer to stoichiometric
temperature levels, around 2000 K levels.
• Develops higher SFC. Therefore used for only shorter duration. An increase of 44% increase in thrust
results in an increase of 164% in SFC
• Size and weight penalties and additional pressure losses in the jet pipe during ‘without afterburning’
• Develops higher noise levels due to high temperature exhaust.
46. Real cycle analysis of engines
• No components (intake, compressor, etc.) develop reversible process. They can be
close to adiabatic. Therefore there is a rise in entropy in intake, compressor, turbine and
• In the burner combustion is never complete. There is a loss in stagnation pressure.
• The gas composition (molecular weight, gas constant) and properties (specific heat
capacities) vary through the engine. However the variation of specific heats will be
approximated by assuming a perfect gas with constant specific heat upstream of the
burner and a perfect gas with different constant specific heats downstream of the main
• Incomplete expansion (or over expansion) to ambient pressure in the nozzle exhaust.
• Extraction of compressor discharge air for the purpose of turbine cooling or for use by
• the airframe.
• Fluid velocities inside the engine are not negligible.
50. Component Characteristics-Compressor
• Compressor performance characteristics ( isentropic efficiency and compressor ratio)
affects the engine performance as a whole.
• Energy spent for compression will decide on the energy available for propulsion
• Higher compressor efficiency is desirable to enhance available energy for thrust
• Pressure ratio influences the engine performance parameters.
• SFC and Specific thrust variation with pressure ratio
• Combustion efficiency increases with pressure ratio
52. Centrifugal Compressor performance
• Non dimensional Analysis and Non dimensional groups
• Curves of Pressure ratio vs mass flow rate
• Curves of Non dimensional groups a
• Curves of Isentropic Efficiency vs Non dimensional Groups