Fundamentals of Gas Turbine Engines

Fundamentals

Energy is the ability to do work.
The SI unit is Joules.
Different forms of energy: Electrical, chemical, heat, nuclear, and mechanical energies.
Energy cannot be destroyed; it can only be converted from one form to another.
Energy will not convert completely into 100% work.

Kinetic Energy
Potential energies due to gravity and the state of a body.
Example: How do you stop an aircraft traveling along a runway with 4MJ of kinetic energy?

A body will remain in its state of rest or, if in motion, will continue to move at a constant velocity unless acted upon by some external force.

The acceleration of an object is directly proportional to the force acting on it and is inversely proportional to its mass, taking place in the direction of the force.
Formula: F = ma
- Where:
  - F = Force
  - m = mass
  - a = acceleration

When stem is closed: Balanced force.
When stem is open: Unbalanced force.
Relates to Newton’s 3rd law of motion
Diagram of a balloon in flight, showing v_0 (initial velocity) and pressure P.
Burners is added -> air temperature is raised -> air velocity increases
Compressor is added -> pressure and airflow are maintained
Relates to Newton’s 2nd law of motion: Thrust = F = m \frac{vj - v0}{t}
- Where:
  - m_f = mass flow
  - v_j = velocity jet
  - v_0 = initial velocity
Diagrams illustrating the flight of a balloon with burners and compressor.
Turbine is placed in the path of the heated air.
Some of the energy drives the turbine, which in turn drives the compressor.
The remaining energy propels hot gases through the stem.
Diagrams include labels for compressor (C), turbine (T), va (air velocity) and vj (jet velocity).

To create the forward reaction, there must be an acting force, known as Thrust.
The gas turbine engine accelerates a stream of air to an exceptionally high velocity to obtain useful thrust from the reaction.
The thrust obtained is proportional to the mass and the acceleration. Force = mass * acceleration.

The same amount of propulsive thrust can be obtained by either:
- Accelerating a LARGE mass through a SMALL increase in velocity (turboprop).
- Accelerating a SMALL mass through a LARGE increase in velocity (turbojet).

Metal tube filled with gunpowder or rapid-burning mixture of chemicals.
Fuel burns and is expelled out from the back of the tube, pushing the rocket forward.
Liquid oxygen in one tank and liquid fuel in the other tank.
Gas rushes out from the nozzle at the back, and thrust is produced.
High velocity exhaust gases.

At high supersonic speeds (M ≥ 2.5), sufficient compression of incoming air can be attained through shock formation at the inlet ram followed by the inlet diffuser.
Commonly used in military UAVs.
Contains no moving parts.
Must be assisted to attain a speed of more than 400km/h before it can be started.
Air is compressed by means of shock formation at high aircraft speed.
Fuel is injected, mixed with air, and burned.
Heated gases are accelerated through the nozzle.

Shutters open to allow air to enter.
Fuel is then mixed with the air and ignited.
As the heated gas expands and leaves the exhaust, pressure decreases, causing the shutter to open again.

Small frontal area.
Ability to take advantage of high ram-pressure ratios.
Derives its thrust by highly accelerating a small mass of air, all of which goes through the engine.
Highest thrust-to-weight ratio.
Low thrust specific fuel consumption (TSFC) at high airspeeds.

Two gas streams: cold bypass air and hot turbine discharged air.
Fan air accounts for 80% of the thrust.
Two types of turbofan:
- low bypass (Bypass ratio < 2:1)
- high bypass (Bypass ratio > 4:1)

Fitted with reduction gearbox to reduce the speed of the propeller to about 1000-2000 rpm.