Test 3 Flashcards
Inlet Airduct
- Is considered to be a part of the airframe
- It is responsible for supplying a constant, undisturbed flow of subsonic air to the compressor
Two types:
- Subsonic inlet duct
- Usually is a divergent duct
- Supersonic inlet duct
- Usually is a convergent duct
Turboprop
- Propeller reduction gearbox interferes w/ airflow
Ways to deliver air:
- Ducted spinner inlet
- Conical spinner inlet
- Under scoop inlet
Foreign Object Damage (FOD)
when something foreign enters the engine
Supersonic Inlet Duct
- Airflow must be SOS entering the compressor so a convergent-divergent duct is used
Bernoulli’s equation at SOS
Bernoulli’s equation switches when going from subsonic to supersonic
Compressors
Two types:
- Axial flow
- Centrifugal
Compressors speed up air, not increase pressure
Axial Flow Compressors
- Air passes straight through the compressor
Disadvantages
- Heavier than centrifugal
- Costly to manufacture
Advantages
- Higher overall compression ratio
- Easier to streamline
Centrifugal compressor
Advantages
- Rugged
- Lightweight
- Easier to manufacture
- High-pressure ratio for each stage of compression
Disadvantage
- Large diameter disk in back
- Tip speed increases and efficiency goes down
- Difficult to streamline
- You can stack centrifugal compressors
Components:
- Impeller (part w/ all the fins)
- Diffusor (stator)
- Manifold
Rotor vs Stator blades
Rotor blades - blades that rotate in the compressor
Stator blades - blades that stay still
Types of Centrifugal Compressors
Double Entry
- Difficult to design inlet ducts for front and rear air supply
Multi-stage
- High pressure rise per stage
Types of Axial flow compressors
- Single spool axial flow
- Dual spool axial flow
- Three spool axial flow
Single Spool Axial Flow
- Limited in # of stages (# of disks)
- Rearmost becomes inefficient
- Front becomes overloaded
- Airflow becomes restricted
Dual Spool Axial Flow
- Rearmost compressor = High pressure Compressor (N2)
- Driven by forward stage turbine (High-pressure turbine)
- N2 compressor is governed by the fuel control and used by the starter to start the engine due to its lighter weight
Three Spool Axial Flow
- Fan = Low pressure (LP) compressor (N1)
- Intermediate pressure (IP) compressor (N2)
- High pressure (HP) compressor (N3)
- All are driven by separate turbines (3 shafts)
Stages of the Three spool axial flow
N1 (fan blade) => N2 compressor => N3 compressor => Diffuser => Combustor => Turbine inlet => High pressure turbine (N3) => Intermediate pressure turbine (N2) => Low pressure turbine (N1) => Exhaust
Blade attachment
- blades are commonly held in place by dovetail or fir tree
- Centrifugal forces will hold blades in place
Compressor Blade Design
Blade twist helps maintain pressure throughout compressor
Diffuser section
- Rear of compressor
- Divergent duct so Velocity decreases and pressure increases
HIGHEST PRESSURE POINT
What is the highest pressure point?
The diffuser section
Surges and Stalls of the compressor
Causes:
- Excessive rotor blade AOA
- Obstruction to inlet
- Excessive pressure in the burner section
- High crosswind on takeoff and low airspeed
- Abrupt flight maneuver
Combustion Section Requirements
- Minimum pressure loss in gas
- High combustion efficiency
- Combustion occurring entirely within the combustor
- Uniform temp distribution throughout gases
- Low risk of flame blowout
Most common types of combustors
- Multi-can
- Can annular
- Annular
Multi-can combustor
- Usually 8-10 cans
- Igniters in only 2 cans
- Crossover tubes connect cans
Advantages
- Individual cans can be removed
Disadvantages
- Uneven temps
- Uneven temps can cause turbine failure
Can-annular
- Consists of individual cans mounted on an annular duct
- Hot gases are collected then directed into the turbine
Advantages
- Individual cans can be removed
- Shorter cans (lower pressure drop)
- Uniform temperatures even with a clogged fuel nozzle
Annular
- Makes the most efficient use of space
- Efficient mixing of fuel with air
- Requires minimum amount of cooling
- Provided even temperature air
- Cannot be replaced without removing the engine from the aircraft
Turbine Section
Two Types:
- Radial inflow turbine
- Axial turbine
There are stators (inlet guide vanes) between the combustion section and the turbine section
Turbine inlet guide vanes
PLACE WITH THE HOTTEST TEMPERATURE
Where is the hottest temperature?
turbine inlet guide vanes
Turbine Blade Design
Reaction blade
- Produce turning force by aerodynamic action (airfoil)
Impulse Blade
- Produce turning force by the energy required to change the direction
of the airfoil
Reaction-Impulse
- A combination of the other two
Turbine Cooling
Flowing compressor bleed air through hollow guide vanes
Turbine Failures
Creep
- Deformation of metal that is continually under high centrifugal loads and temperatures
Metal fatigue
- Weakening of metal subjected to repeated cycles
Corrosion
- Electrolytic action that occurs when alloying agents combine w/ elements in the air to form salts
- Accelerated by exposure to extremely high temps
Exhaust gases
- The exhaust system can be used to accelerate air using Bernoulli’s principle to increase thrust
- Uses a chocked bore nozzle
Variable Area nozzle
- opens/closes based on fuel flow
Noise suppressors
- Amount of noise relates to the velocity of the exhaust gases
- Reduces efficiency
Noise suppressors
- Amount of noise relates to the velocity of the exhaust gases
- Reduces efficiency
Thrust Reverser
- Used to assist brakes when landing
- Diverts 40-50% of engines forward thrust rearward
Vector thrust
Changing direction of exhaust nozzle or turbine engine entirely
Vector thrust
Changing direction of exhaust nozzle or turbine engine entirely
