Turbine Engine Compressor Section

Compressor Section

• The compressor section supplies air to the combustor and converts fuel energy and mechanical work into potential energy.
• Compression occurs through the acceleration of a working fluid followed by diffusion, resulting in a pressure rise.
• The primary purpose of the compressor is to increase the pressure of the air entering the engine inlet and discharge it to the diffuser and then to the combustor section at the correct velocity, temperature, and pressure.
• Compressor efficiency is based on the principle of maximum compression with the least temperature rise.

Temperature Rise in the Compressor

• Temperature rise in the compressor is caused by compression and friction.
• The colder the air entering the combustor, the greater the rise in temperature during the combustion process.

Axial Flow Turbojet

• Axial flow turbojet compressors must flow air at a velocity of 120-150 m/s (400-500 ft/s) and raise its static pressure 20-60 times in a short engine length.

Centrifugal Flow Compressors

• The centrifugal flow compressor is the oldest design and is still in use today.
• Advantages of centrifugal flow compressors include:
  • Light weight
  • Ease of construction
  • Ruggedness
• A centrifugal flow compressor assembly consists of:
  • An impeller rotor
  • A diffuser
  • A manifold

Impeller

• The impeller is usually made from aluminum alloy or titanium alloy and can be either single- or dual-sided.
• The diffuser provides a divergent duct in which the air spreads out, slows down, and increases in static pressure.
• The compressor manifold distributes the air in a turbulence-free condition to the combustion section.

Stator Vanes

• Stator vanes are the stationary blades located between each row of rotating blades in an axial flow compressor.
• Stator vanes act as diffusers for the air coming off the rotor, decreasing its velocity and raising its pressure.
• Stator vanes also help prevent swirling and direct the flow of air coming off each stage to the next stage at the appropriate angle.

Variable Stator Vanes

• Some stator vanes can be variable in angle, similar to inlet guide vanes.
• Variable stator vanes can be used to maintain airflow directed at the correct angle to the succeeding rotors.

Compressor Pressure Ratio

• The compressor pressure ratio is determined by measuring the total pressure after the last stage of compression and dividing it by compressor inlet total pressure.
• The compressor pressure ratio can also be described in terms of pressure ratio per stage.

Compressor Taper

• As pressure builds in the rear stages of the compressor, velocity tends to drop in accordance with Bernoulli's principle.
• Velocity rises and falls through the successive stages of the compressor, but maintains approximately the same inlet and outlet velocity.

Compressor Bleed System

• The compressor bleed system automatically dumps away unwanted air to prevent aerodynamic disturbance.
• The system is used in some engines at low and intermediate speeds to maintain the correct airflow and pressure ratio.
• The compressor bleed system is typically scheduled closed at high rotational speeds.