GAS TURBINE OPERATION Flashcards
What is the minimum on all Gas Turbine Engines?
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On all gas turbine engines it will minimally include the compressor. combustion chamber. and turbine (Figure 3.1-3). Additionally, on a turbofan, turboprop and turboshaft, it will include their respective fan, propeller or rotor blades. Each of these components plays a vital role in the production of thrust.
BRAYTON CYCLE consist of 4 events that occur simultaneously. 1 2 3 4
1 INTAKE 2. COMPRESSION 3. COMBUSTION 4. ESHAUST THE BRAYTON CYCLE A gas turbine engine follows a cycle of operation known as the Brayton Cycle (Figure 3.1-4). This operating cycle consists of four events which occur simultaneously: intake. compression. combustion and exhaust. It is important to note that this cycle of operation is different than the operating cycle of a reciprocating engine.
- Describe the relationship between pressure and velocity in a closed system.
- Together they make up total pressure.
- How does subsonic airflow react through a convergent opening? A divergent opening?
- Convergent: velocity increases and pressure decreases. Divergent: velocity decreases and pressure increases.
- How does supersonic airflow react through a convergent opening? A divergent opening?
- Divergent: velocity increases and pressure decreases. Convergent: velocity decreases and pressure increases
- What happens to the airflow as it passes through a nozzle? A diffuser?
- Nozzle: velocity increases and pressure decreases. Diffuser: velocity decreases and pressure increases.
- What are the three sections of a gas generator?
- Compressor, burner, turbine.
Q-9B-0020K Sheet 4 of 4
- How does a gas turbine engine produce thrust?
- By rapidly compressing, heating and accelerating a large quantity (mass) of air and fuel.
FOR TRAINING USE ONLY 503
TRAINEE GUIDE Q-9B-0020K Assignment Sheet 5-1-3 Sheet 2 of 4
7. What cycle explains the movement of air through a gas generator?
- Brayton Cycle.
- What happens to the velocity of the gases as they pass through the compressor section? The burner section? The turbines?
- Compressor: Remains fairly constant. Burner and turbine: Increases.
- What is gross thrust?
- Thrust measured at exhaust at standard day conditions 29.92 and 15 °C.
- What is net thrust?
- Thrust measured under normal flight conditions.
- When are gross thrust and net thrust equal?
- When aircraft is in a static position and standard day conditions.
- What affects the density of the air mass?
- Temperature, pressure, and altitude.
- What happens to thrust when air density decreases?
- Thrust decreases.
- What happens to thrust when air temperature increases?
- Thrust decreases.
- What happens to thrust when air pressure decreases?
- Thrust decreases.
- What is the relationship between pressure and temperature as altitude increases?
- Temperature and pressure both decrease with an overall decrease in thrust.
- What is the optimum cruise altitude and why?
- Approximately 36,000=, temperature remains isothermal (A line of equal or constant temperature on a graph or chart, such as a weather map) No more decrease in Temp.
- How does airspeed and the ram effect change the amount of thrust produced at subsonic and supersonic airspeedS?
- Airspeed increase without ram effect causes thrust to decrease.
Airspeed increase with ram effect causes thrust to remain relatively constant at subsonic speeds and increased greatly at supersonic speeds.
Recall that increasing the pressure of airflow will increase its potential energy, while
increasing the velocity of airflow will increase its kinetic energy.
In a gas turbine engine, the inlet, compressor, and diffuser sections build the potential energy of the airflow. In the burner, turbine and exhaust sections, this potential energy, along with the energy from fuel ignition, is converted into kinetic energy. The kinetic energy is then used for thrust production. Therefore, in the first half of a gas turbine engine, high pressures are desired, while high velocities are desired in the second half.
WHY IS THE HI PRESSURE COMPRESSOR AFT OF THE LOW PRESSURE COMPRESSOR?
A basic law of aerodynamics states that the speed of sound increases as the air temperature increases. Since the air temperature is increased through the compression phase, the high-pressure compressor can attain higher speeds without exceeding the speed of sound (Mach). Also, the blades of the high-pressure compressor are shorter than those of the low-pressure compressor, and can turn faster before exceeding their limiting Mach number.
