Gas Turbine Engine - Lecture Flashcards

Flashcards covering key concepts from the Gas Turbine Engine lecture notes.

What are the three main types of gas turbine engines?

Turbojet, turbofan, and turboprop.

What distinguishes a turbofan from a turbojet?

A turbofan has a large Fan located in the intake and only part of the air goes into the core; most air bypasses the core.

In a turboprop engine, where is the propeller located and what primarily generates thrust?

A propeller is attached to one of the shafts; most thrust is produced by the propeller.

What is ram recovery in the air intake?

A pressure rise as air slows in a divergent duct, improving efficiency and flow through the engine.

What is a pitot-type (single entrance) air intake and its main drawback?

Air travels straight to the compressor; simple and short, but performs poorly at extreme attitudes/high angles of attack.

What is a divergent duct in an air intake and why is it used?

An intake where area increases toward the compressor; slows air and increases pressure (ram recovery) to improve efficiency.

Why is ice protection important for air intakes and how is it achieved?

To prevent ice buildup that can restrict airflow; protection systems (often using bleed air) prevent or remove icing.

What happened in the 1982 Boeing 737 incident related to engine ice protection and EPR?

Ice blocked the EPR sensor due to not activating ice protection, causing false thrust readings and reduced thrust.

What is the primary function of the compressor?

Increase the pressure of the incoming air to enable higher combustion energy and thrust.

What are the two main compressor types used in gas turbine engines?

Centrifugal compressor and axial-flow compressor.

Describe a centrifugal compressor.

Air is directed toward a rotating impeller, accelerated outward by centrifugal force; a diffuser converts kinetic energy to pressure; typical pressure ratio ~7:1.

What is a major disadvantage of centrifugal compressors?

Inefficiency when airflow must change direction; not ideal for large thrust; mainly used in smaller engines.

Describe an axial-flow compressor.

Air flows straight through; rotor blades accelerate air rearward; stator blades diffuse to convert velocity to pressure; multiple rotor/stator stages increase pressure.

What is a pressure stage in an axial-flow compressor?

A rotor/stator pair that increases pressure by about 1.2:1 per stage.

What is a 'spool' in a gas turbine engine?

A combined compressor, shaft, and turbine; can have multiple spools that may be independent.

What defines a two-spool engine?

Two compressor sections (low and high pressure) each driven by its own turbine, allowing optimum speeds.

What defines a three-spool engine?

An intermediate compressor adds a third spool with its own turbine for more RPM optimization.

What is the big challenge in the combustion section?

Maintaining stable and efficient combustion over a wide range of conditions (altitude, temperature, pressure, g-load).

Why is a diffuser used before the combustion chamber?

To slow down the high-velocity air after compression so combustion can be stable and flame blowout is avoided.

What is the primary zone in a typical combustion chamber?

The initial roughly 20% of air that passes the fuel nozzle and participates in the initial combustion.

What is the dilution zone in the combustion chamber?

The remaining ~80% of air is directed around the primary zone to cool and sustain combustion along the chamber.

Name the three main types of combustion chambers.

Can (cans around the shaft), Can-annular (Cannular), and Annular (around the shaft).

What is a Can combustion chamber?

Multiple cans around the shaft, each with its own duct; easy to service but space-inefficient.

What is a Cannular combustion chamber?

Cans inside an annular chamber; better space usage and easier ignition due to interconnection.

What is an Annular combustion chamber?

Combustion chamber surrounds the shaft in one annular space; efficient air use but harder to maintain.

What is the turbine section designed to do?

Extract energy from hot gases to drive the compressors and other components; consists of stationary vanes and rotating blades on shafts.

Why are turbine components built from special heat-resistant materials?

They operate at extreme temperatures (often >1000 C); cooling may be required for blades to survive.

What does the exhaust section include and what is its purpose?

Tailpipe, tail cone, and exhaust nozzle; to collect/straighten gases, then accelerate them to produce thrust.

How is exhaust flow treated differently in low bypass vs high bypass turbofans?

In low bypass, cold bypass air is mixed with hot exhaust in the exhaust; in high bypass, mixing often occurs past the nozzle.