EXTRA TURBINE NOTES

Question 1

Recall that increasing the pressure of airflow will increase its_________, while increasing the velocity of airflow will increase its ____________. In a gas turbine engine, the inlet, compressor, and diffuser sections build the potential energy of the airflow. In the burner, turbine and exhaust sections, this potential energy, along with the energy from fuel ignition, is converted into kinetic energy. The kinetic energy is then used for thrust production. Therefore, in the first half of a gas turbine engine, high pressures are desired, while high velocities are desired in the second half.

Answer 1

potential energy

kinetic energy

Question 2

KINETIC ENERGY

Answer 2

kinetic energy (KE) of an object is the energy that it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes.

Question 3

PURPOSE OF TURBINE SECTION

Answer 3

Purpose of the turbine section?

Convert the accelerated hot gas from the combustion chamber into energy to turn the compressor section.

Question 4

This is done by attaching the fan directly to the compressor. In either instance, the gas generator turbine section will extract ___ percent of the total energy that leaves the burner section just to turn the compressor and accessories. The remaining____ percent will be used for thrust. Part of the 25 percent will be converted to mechanical energy through the turbines to drive the fans. The other part will exit the exhaust section as kinetic energy.

Answer 4

75

25

Question 5

BYPASS RATIO

Answer 5

The amount of air that bypasses the gas generator in comparison with the amount of air that passes through the gas generator is called the bypass ratio. This ratio ranges from about 1 to 5 or more

Question 6

BRAYTON CYCLEA gas turbine engine follows a cycle of operation known as the Brayton Cycle. This operating cycle consists of four events which occur simultaneously:

Answer 6

INTAKE
COMPRESSION
COMBUSTION
EXHAUST

Question 7

Highest pressure is after the________ before the burner

Answer 7

diffuser

Question 8

Highest temperature is after the__________, before the turbine

Answer 8

burner

Question 9

Highest velocity is after the ___________.

Answer 9

exhaust nozzle

Question 10

The factors that affect the thrust of a gas turbine engine include

Answer 10

AIR DENSITY
AIRSPEED/RAM EFFECT
ENGINE RPM

Question 11

If the density of air increases, mass will increase, and therefore thrust will _____________

Answer 11

INCREASE

Question 12

As air temperature increases, air molecules tend to move apart. This results in a density decrease, and a resultant ___________ in thrust

Answer 12

DECREASE

Question 13

As air pressure increases, air molecules tend to move closer together. This results in an increase in density, and therefore, thrust__________.

Answer 13

INCREASE

Question 14

With an increase in altitude, however, the rate of thrust decreases because a pressure drop is greater than the thrust increase resulting from a temperature drop. This means an engine will produce _________ as it increases in altitude

Answer 14

less thrust

Question 15

At approximately 36,000 feet (beginning of the isothermal layer), temperature stabilizes. As a result, temperature will no longer offset the density decrease due to pressure. Therefore, thrust decreases more rapidly. This altitude is also known as the _______________ At this altitude, thrust available plus low fuel flow and diminished drag combine to provide optimum performance for many engines

Answer 15

optimum cruise level.

Question 16

One of the most obvious factors that affects the thrust output is the rotational speed of the engine. With an increase in RPM, there is an increase in thrust. However, at low RPM there is very little increase in thrust with an increase in throttle. At higher rates of revolution, a small increase in throttle setting will produce a_______ increase in thrust

Answer 16

large

Question 17

At lower settings, fuel consumption is high for the amount of thrust produced. For this reason, gas turbine engines are normally operated at or near their __________ RPM

Answer 17

maximum

Question 18

Engine Pressure Ratio (EPR): The EPR gauge indicates the pressure ratio between the ______________. The EPR gauge is more widely used because it automatically accounts for some of the airflow variations at the inlet

Answer 18

inlet and exhaust airflow

Question 19

EGT (Exhaust Gas Temperature): Measured aft of the ________ section

Answer 19

turbine

Question 20

TIT (Turbine Inlet Temperature): Temperature of the gases from the ________________ of the engine as they enter the first stage of the turbine
TIT is the highest temperature inside a turbine engine and is difficult to measure which is why EGT is often measured instead

Answer 20

combustion section

Question 21

The primary function of the compressor:

Answer 21

1. is to supply enough air to satisfy the requirements of the combustion section. Specifically, the compressor increases the pressure of the airflow from the air inlet duct and directs it to the burners in the quantity and at the pressures required.
2. A secondary function is to supply compressor bleed air to operate various components throughout the engine and aircraft

Question 22

Because the compressor section receives energy from the turbine via the drive shaft, it is not a closed system. Therefore, the increase in velocity will not result in a decrease in pressure. In fact, both velocity and pressure will increase in the compressor section and therefore, total ______________.

Answer 22

pressure increases

Question 23

Axial flow compressor
The term axial-flow applies to the axial (straight line) flow of air through the compressor section of the engine. An axial-flow compressor has two main elements: Rotor blades and stator vanes.
Rotor blades are \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Stator vanes are \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Each rotor and stator pair forms a stage

Answer 23

rotating, airfoil shaped blades

stationary airfoil-shaped blades

Question 24

Efficient use of multiple stages can produce very high overall ___________ ratios

Answer 24

compression

Question 25

Since the air temperature is __________ through the compression phase, the high-pressure compressor can attain higher speeds without exceeding the speed of sound (Mach). Also, the blades of the high-pressure compressor are shorter than those of the low-pressure compressor, and can turn faster before exceeding their limiting Mach number

Answer 25

increased

Question 26

Usually, the rear compressor rotor is speed-governed by the engine fuel control and is the rotor to which the engine ________ is connected

Answer 26

starter

Question 27

The rear compressor, or high-pressure compressor, is connected by a hollow shaft to a high-pressure turbine. This is the high rotor. The rotors are sometimes called spools, such as the “high spool.” In this text, we will use the term rotor. The high rotor is often referred to as ___ for short.

Answer 27

N2

Question 28

The low-pressure compressor is connected to the low-pressure turbine by a shaft that goes through the hollow shaft of the high rotor. The low-pressure rotor is called____for short

Answer 28

N1

Question 29

Guide Vanes – In addition to the rotors and stators, the compressor utilizes inlet and exit guide vanes

Answer 29

GOOD TO KNOW

Question 30

Inlet guide vanes

Answer 30

Inlet guide vanes impart a swirling motion to the air entering the compressor in the direction of engine rotation. This motion improves the aerodynamic characteristics of the compressor by reducing the drag on the first-stage rotor blades

Question 31

The diffuser is located after the compressor, and it prepares the airflow for the burner chamber. The diffuser _________ the velocity, which gives the airflow a final pressure ___________. The airflow velocity must decrease slightly to avoid blowing out the burner flame, and the increase in pressure helps combustion and fuel efficiency

Answer 31

decreases

increase

Question 32

Exit guide vanes,

Answer 32

Exit guide vanes, also known as straightening vanes, are located at the discharge end of the compressor. They are the last set of stator vanes which prepares the airflow for the diffuser by straightening the airflow to reduce the airflow turbulence as it comes off the rotational movement of the compressor

Question 33

Air from the compressor entering the burner section will be divided into two types: _________________

Answer 33

primary and secondary air

Question 34

_____________ percent is primary air, and it is mixed with fuel for combustion

Answer 34

Twenty-five

Question 35

The remaining______ percent is secondary air, it flows around the chamber and through the small holes and louvers to cool the thin walls and control the flame. This unburned air can also be used to help cool the turbine

Answer 35

75

Question 36

Burner must withstand very high temperatures and also minimize pressure________ through the burner

Answer 36

decrease

Question 37

Like the compressor, the turbine section is comprised of stators and rotors. However. the turbine section drives the __________________. It is also designed to__________ airflow velocity. This acceleration occurs through the stators, rotors, or both

Answer 37

compressor and the accessories

increase

Question 38

The stator element is sometimes called stationary stator vanes, turbine, nozzle guide vanes, turbine guide vanes, or just plain nozzles. Stator vanes come before the rotors in the turbine section. The function of the stator vanes is twofold.
1.
2.

Answer 38

1. First, it prepares the airflow from the combustion chamber for the harnessing of power by the turbine rotor.
2. Second, the stators deflect the gases at a specific angle in the direction of turbine wheel rotation

Question 39

A dual-spool compressor will require _________ driving the compressors via separate shafts

Answer 39

dual turbines

Question 40

The ____________ is the most highly stressed part of the engine. Not only must it operate at temperatures nearing 2,000° F (monitored in the cockpit), but it must do so while undergoing severe centrifugal loads imposed by rotational speeds of over 10,000 rpm. The higher the temperature the turbine section can bear, the higher the_____ that can be produced

Answer 40

turbine section

thrust

Question 41

Blades undergo ___________, as they are heated. This is a cumulative process, and excessive temperatures over long periods may result in permanent blade deformation. Deformed blades will not operate efficiently and may fail catastrophically causing severe damage and possible injury or death to personnel

Answer 41

elongation, or “creep”

Question 42

The exhaust cone collects the exhaust gases discharged from the turbine assembly and gradually converts them to a_________.

Answer 42

solid jet

Question 43

The exhaust section of the turbojet engine is constructed of several parts, each of which has its individual functions. Although the parts have individual purposes, they have one common function. They must direct the flow of hot gases rearward to cause a _________ to the gases while preventing turbulence

Answer 43

high exit velocity

Question 44

Where does bleed air come from and what is it used for?

Answer 44

A stage in compressor (varies w/ engines). It is used for pressurization, heating, air conditioning, anti-ice, pneumatics.