M15.4 Compressors Flashcards
What is the primary function of the compressor in a gas turbine engine?
To supply a sufficient quantity of air to satisfy the requirements of the combustion chamber.
What are the two main components of a compressor?
- Compressor rotor
- Compressor stator
What is the role of the rotor in a gas turbine compressor?
To suck in air and push it to the outlet side, increasing the energy of the airflow.
What is the function of the stator in a gas turbine compressor?
To guide and slow the airflow to cause an increase in pressure.
What is a compressor stage composed of?
A rotor and a stator.
What are inlet guide vanes (IGVs)?
Fixed or movable stator vanes in front of a compressor stage that improve airflow into the first compressor stage.
What are outlet guide vanes (OGVs)?
Stator vanes in the fan duct that improve airflow into the fan nozzle.
What are the two types of compressors used in gas turbine engines?
- Centrifugal flow compressor
- Axial flow compressor
What is a characteristic of centrifugal-flow compressors?
They have a high-pressure rise per stage, around 8:1.
What are the main components of a centrifugal flow compressor?
- Impeller (rotor)
- Diffuser (stator)
- Compressor manifold
What is the typical limitation of centrifugal compressors?
Limited to two stages due to efficiency concerns.
What is the main function of the impeller in a centrifugal compressor?
To pick up and accelerate the air outwardly to the diffuser.
What is the advantage of axial flow compressors in terms of airflow?
They compress air while maintaining the original direction of flow, avoiding energy loss.
Where are axial flow compressors typically found?
On turbofan engines widely used in aviation.
What is the structure of an axial flow compressor?
It consists of rotating components with aerofoil-shaped blades and stationary vanes mounted to the casing.
What is a single-spool compressor?
A compressor with a single drum and multiple stators.
What is a multi-spool compressor?
A compressor consisting of two or three drums of rotors, each driven by a separate turbine segment.
What are the advantages of centrifugal flow compressors?
- High pressure rise per stage
- Efficiency over a wide rotational speed range
- Simplicity of manufacture and low cost
- Low weight
- Low starting power requirements
What are the disadvantages of centrifugal flow compressors?
- Large frontal area for a given airflow
- Losses in turns between stages
What are the advantages of axial flow compressors?
- High peak efficiencies
- Small frontal area for given airflow
- Straight through flow allowing high ram efficiency
- Increased pressure rise with negligible losses
What are the disadvantages of axial flow compressors?
- Good efficiencies only over a narrow rotational speed range
- Difficulty of manufacture and high cost
- Relatively high weight
- High starting power requirements
What causes compressor stall?
Changes in the angle of attack due to rotor speed or inlet velocity changes.
What is compressor surge?
A severe form of compressor stall characterized by rapid airflow decrease and blockage.
What are two operational reasons for compressor stall and surge?
- Engine speed too far below design speed
- Incorrect acceleration or deceleration
What is one method to prevent compressor stall and surge?
Use of compressor bleed valves.
What is the moment weight of a fan blade?
The product of the blade mass and the distance of the center of gravity from the rotational axis.
What happens if the moment weight of a fan blade changes due to blending?
The original weight is crossed out and the new moment weight is marked on the root.
How are fan blades matched on a fan disc?
Using computerized balancing to determine the best position for each blade.
What is the best method to change a single fan blade?
Replace it with a new blade that has a moment weight as close as possible to the old one.
What can cause airflow separation in a compressor?
Increased angle of attack on rotor blades and stator vanes.
What are the three design methods to prevent compressor stall and surge?
- Use of compressor bleed valves
- Use of dual or triple-spool rotors
- Use of variable compressor stator vanes
What can cause a blockage to the airflow in an aircraft engine?
Compressor stall and surge
What are the two operational reasons for compressor stall?
- Speed of the engine too far below design speed
- Incorrect acceleration or deceleration
Name one method to avoid compressor stall and surge.
Compressor bleed valves
What is another method used to prevent compressor stall and surge apart from bleed valves?
Dual or triple-spool rotors
What is the most modern method to prevent compressor stall?
Variable compressor stator vanes
How do compressor bleed valves function?
They are open at low engine speeds to allow excessive airflow to escape overboard
Where are bleed valves typically located in an aircraft engine?
In the mid-section and sometimes in the aft section of the engine compressor
What are the two parts of a dual spool engine called?
- Low-pressure compressor (N1 compressor)
- High-pressure compressor (N2 compressor)
What is the advantage of variable stator vanes?
They allow for an optimum angle of attack on the following rotor blades for every engine speed
What is a disadvantage of variable stator vanes?
They require a very complicated control mechanism
What does the compression ratio of an internal combustion engine represent?
The ratio of the volume of its combustion chamber from its largest to its smallest capacity
What is the pressure ratio per stage in an axial flow compressor?
About 1.3:1
If the air pressure entering the first stage of an axial flow compressor is 10 psi, what will the output pressure be after the first stage?
13 psi
How do you calculate the output pressure of subsequent stages in a compressor?
Multiply the input pressure by the pressure ratio of 1.3
True or False: The axial velocity of gas in a compressor remains constant from the front to the rear.
True
Fill in the blank: The pressure increase at each stage of a compressor is very _______.
small
What is necessary to raise the pressure to high values for efficient combustion in a compressor?
Many stages
