Test 3 Flashcards
(39 cards)
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
