Engines Ch.2

Front 1

Describe purpose and the types of inlet ducts.

Back 1

inlet ducts: designed to provide the proper amount of high pressure, turbulence-free air to the compressor.

Single entrance inlet duct: simplest and most effective design. Directly in front of the engine. Long duct. Length might result in slight pressure loss, it is offset by smooth airflow characteristics.
Divided intrance inlet duct: reduces friction loss, pilot can sit lower. Distorts incoming air due to side location. cant be large without increasing drag.

Front 2

State the operation and shape of subsonic and supersonic inlet ducts.

Back 2

Subsonic:
Divergent shaped
increases pressure, decreasing velocity
Supersonic:
Designed differently due to high compressibility at supersonic speeds
Initially converge, then diverges.
slows air to subsonic speeds, pressure increases. Then, it diverges, increasing the subsonic air's pressure to send to the compressor.

Front 3

State the function of a variable geometry inlet duct.

Back 3

It utilizes mechanical devices such as ramps, wedges, or cones to change the shape of the inlet duct as the aircraft speed varies between subsonic and supersonic.

Front 4

State the function of the compressor section.

Back 4

To supply enough air to satisfy the requirements of the combustion section.

Front 5

Describe the centrifugal flow compressor used in gas turbine engines, including their advantages and disadvantages.

Back 5

Centrifugal flow compressor:
Air enters the impeller, the impeller accelerates the air outward toward the diffuser. The high rotational speed increases airflow velocity. It passes through divergent passages, increasing pressure. Since velocity and pressure is increased, total pressure increases. Then air passes through the diffuser through divergent passages, decreasing velocity, increasing pressure, keeping total pressure constant. Airflow then passes through the compressor manifold, which directs it to the combustion chamber.
Advantages:
-Rugged
-Low cost
-Good power output over a wide range of RPM's
-High pressure increases per stage
Disadvantages:
-Large frontal area required
-Impractical for multiple stages

Front 6

State the function of the burner section.

Back 6

contains the combustion chamber, and provides the means for proper mixing of the fuel and air to assure good combustion.

Front 7

Describe the three types of combustion chambers used in gas turbine engines, including their advantages and disadvantages.

Back 7

Can: airflow ducts to combustion cans around the burner section. Each can has own fuel nozzle, burner liner and casing. Primary air at nozzle supports combustion, while secondary air flows through, between, and around the liner and burner case to provide cooling.
Advantages:
strong, durable, easy maintenance. Individual units can be inspected or replaced
Disadvantages: poor use of space in chamber, greater pressure loss, uneven heat distribution to the turbine section.
Annular combustion chamber:
consists of a continuous, circular, inner and outer shroud around the outside of the compressor drive shaft. Liner is often called a burner basket or basket. Many holes to allow cooling air inside. Fuel introduced through series of nozzles , mixing and igniting with incoming air.
Advantages: uniform heat distribution, better mixing of air and fuel, better use of available space.
Disadvantages:
cannot be removed without disassembling engine, structural problems,
Can-Annular type
cans at front where fuel and air mixed and burned. Hot gases then pass to the annular area of the chamber where they are mixed.
Advantages:
even temp distribution, structural stability, lower pressure loss, efficient
Disadvantages:
expensive

Front 8

State the function of the turbine section

Back 8

It drives the compressor and the accessories. Designed to increase airflow velocity.

Front 9

State the effects of thermal stress on turbine components.

Back 9

Creep, do not operate efficiently, possible catasrophical failure

Front 10

Describe "fir tree" and "creep"

Back 10

fir tree: turbine blade attachment method that prevents the thin metal blades from cracking at the attachment points by allowing them to expand when heated.
creep: Blade elongation

Front 11

Describe the Axial-Flow compressor and its advantages/ disadvantages.

Back 11

Rotors driven by turbine at high speeds, increasing velocity and pressure of the incoming airflow, increasing total pressure. Air pushed through stator vanes, which act like diffusers, air velocity decreases with increasing pressure.
Advantages:
High peak efficiencies, small frontal area reduces drag, straight through-flow allowing high ram efficiency, combustion efficicent (more stages), with dual spool the starting flexibility is greater and improved high altitude performance
Disadvantages:
airflow decreases in compressor at low inlet speeds, high temps at high speeds that result in low compression, efficient only over a narrow rotational-speed,
difficult to manufacture/high cost, high starting power requirements

Front 12

Describe the Axial-Centrifual Flow compressor and its advantages/ disadvantages.

Back 12

Combines axial and centrifugal
Advantages:
large pressure increase, small size useful on helicopters and small aircraft

Front 13

Explain how heat and potential energy are converted into mechanical energy in the turbine section.

Back 13

The turbine's rotor section converts heat and potential energy of the hot expanding gases from the burner chamber into mechanical energy.

Front 14

State the function of the exhaust section.

Back 14

Directs the flow of hot gases rearward to cause a high exit velocity to the gases while preventing turbulence.

Front 15

Describe subsonic and supersonic exhaust nozzles.

Back 15

Subsonic:
convergent
take slow subsonic gases from turbine section, accelerates them.
Supersonic:
Convergent-divergent
high pressure from turbine is pushed toward convergent exhaust section, increasing velocity. In order for velocity increase to continue, volume must increase (divergent area)

Front 16

State the function of the afterburner.

Back 16

Increases the maximum thrust available from an engine by 50 percent or more.

Front 17

Describe the components and operation of the afterburner.

Back 17

Spray bars: introduce fuel to the afterburner and are located in the forward section of the duct.
Flame holders:
provides a region in which airflow velocity is reduced and turbulent eddies are formed. Allows proper mixing of fuel and air for combustion.
Screech Liners:
To control screech (loud noise and vibration), these inner sleves are installed. Reduce pressure fluctuations and vibrations by acting as a form of shock absorber. Have thousands of holes to do so.
Variable Exhaust Nozzle:
leaf arrangement of thin metal plates, it can close for basic engine subsonic operation, or open to allow the gases to expand at the proper rate when the afterburner is being used. Prevents backpressure from gases building up.