Basic Turbine Engine Theory

Question 1

Describe Newton’s third law of motion and its practical application as it relates to the operation of a turbine enginee

Answer 1

Every action, theres equal and opposite reaction.

Jet engine - action of discharging air out the rear of the engine causes a reaction (aircraft and engine moves forward)

Question 2

Describe how gas undergoes changes in pressure, volume and temperature in accordance with Boyle’s and Charles’ Laws

Answer 2

Boyles law - For a fixed amount of an ideal gas kept at a fixed temperature, P (pressure) and V (volume) are inversely proportional. And where temperature is constant

PV = k where k is a constant meaning as Pressure Increases, volume decreases.

(Breathing, breath air in, increase volume of chest cavity, reduce pressure in chest cavity).

Charles law - if a gas is heated, it expands at a rate thats predictable. Pressure is constant

V / T = k (k is constant) volume is directly proportional to Temperature.

example ( as fuel is ignited, it heats air inside balloon causing it to expand, therefore its density to decrease making it lighter then air around it.)

Question 3

Describe each of the following and their application to turbine engine operation—
(a) Bernoulli’s Theorem (what it is and how jet engines use it)

Answer 3

In the streamline flow of an ideal fluid. The sum of the variables is a constant. Variables static pressure and speed of air, as one increases other must decrease.

Inlet duct at front of engine is divergent (gets bigger) for more air suction, consequently its pressure, temperature and density all increase. At exhaust of the engine its convergent which forces air to flow faster meaning more thrust is developed.

Question 4

Describe each of the following and their application to turbine engine operation—
(b) Brayton constant pressure cycle

Answer 4

Notability

Question 5

Describe each of the following and their application to turbine engine operation—
(c) the pressure-temperature cycle

Answer 5

Notability

Question 6

Describe the changes to pressure, temperature and velocity of the gas flow as it passes through each section of a turbine engine.

Answer 6

Pressure - air enters intake it increases in speed, pressure drops. Causing a suction and high humidity days cause condensation.

The compressor stages compress air increasing pressure. (Velocity increases as pressure falls, and increased velocity spins turbine and is then directed out the exhaust.

Temperature - as it works through compressor, temp increases. As it flows over the turbine section it cools again, with further cooling during exhaust section.

Velocity - aim of turbine to have highest velocity of air at the engine exhaust. Velocity remains constant until exhaust.

Question 7

Describe the changes in the airflow characteristics of velocity, temperature and pressure through a divergent and convergent duct at subsonic and supersonic speeds.

Answer 7

at subsonic speeds, convergent ducts are use to convert kinetic energy into pressure energy. At supersonic speeds the opposite occurs, a divergent duct will experience an increase in velocity and a decrease in pressure, temperature and density.

6. SUBSONIC
   Divergent Duct-
   Velocity decreases, Temperature and Pressure increase.
   Convergent Duct-
   Velocity increases, Temperature and pressure decrease.

SUPERSONIC
Divergent Duct-
Velocity increases, Temperature and Pressure decrease.
Convergent duct-
Velocity decreases, Temperature and Pressure increase