Turbine Engine Principles Flashcards

The operation of a gas turbine engine is described by the Brayton cycle. Which of the following represents the correct sequence of the four events in an ideal Brayton cycle?

Answer: Compression, Combustion, Expansion, Exhaust

The ideal Brayton cycle consists of four processes: isentropic compression (in the compressor), constant-pressure heat addition (in the combustor), isentropic expansion (in the turbine), and constant-pressure heat rejection (exhaust). This is best summarized as Compression, Combustion, Expansion, and Exhaust.

In a gas turbine engine, what is the primary function of the diffuser section located between the compressor and the combustion chamber?

Answer: To decrease the velocity and increase the pressure of the air.

The diffuser is a duct with an expanding internal diameter. Its purpose is to slow down the high-velocity air leaving the compressor, converting its kinetic energy into potential energy in the form of increased static pressure. This high-pressure, low-velocity air is ideal for efficient combustion.

Which of the following is a primary advantage of an axial-flow compressor compared to a centrifugal-flow compressor in large, high-performance turbine engines?

Answer: Greater efficiency and ability to handle high mass airflow.

Axial-flow compressors are capable of handling a very large mass of air for a given frontal area and can achieve very high overall compression ratios with high efficiency through multiple stages. This makes them ideal for large engines where high thrust and fuel efficiency are required. Centrifugal compressors typically have a higher pressure rise per stage but are limited in overall mass airflow and are less efficient in very large applications.

A modern commercial airliner is typically powered by high-bypass turbofan engines. What is the main benefit of having a high bypass ratio?

Answer: Improved fuel efficiency and reduced engine noise.

In a high-bypass engine, a large volume of air is accelerated by the fan and bypasses the engine core. This large mass of slower-moving air produces the majority of the thrust more efficiently than a smaller mass of high-velocity gas from the core. This results in significantly better thrust-specific fuel consumption (fuel efficiency) and lower noise levels.

While a gas turbine engine's ultimate purpose is to produce thrust, what is the primary role of the turbine section within the engine?

Answer: To extract energy from the hot gases to drive the compressor and accessories.

The primary function of the turbine section is to extract kinetic and thermal energy from the high-velocity gases leaving the combustion chamber. This extracted energy is converted into mechanical work to rotate the main shaft, which in turn drives the compressor section and engine-driven accessories like fuel pumps and generators.

The production of thrust in a turbine engine is best explained by which physical principle?

Answer: Newton's Third Law of Motion

Newton's Third Law states that for every action, there is an equal and opposite reaction. A turbine engine produces thrust by taking in a mass of air and accelerating it out the back at a high velocity (the action). The engine and the aircraft are then pushed forward by an equal and opposite force (the reaction).