EXTRA TURBINE NOTES Flashcards
(44 cards)
Recall that increasing the pressure of airflow will increase its_________, while increasing the velocity of airflow will increase its ____________. 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.
potential energy
kinetic energy
KINETIC ENERGY
kinetic energy (KE) of an object is the energy that it possesses due to its motion.[1] It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes.
PURPOSE OF TURBINE SECTION
Purpose of the turbine section?
Convert the accelerated hot gas from the combustion chamber into energy to turn the compressor section.
This is done by attaching the fan directly to the compressor. In either instance, the gas generator turbine section will extract ___ percent of the total energy that leaves the burner section just to turn the compressor and accessories. The remaining____ percent will be used for thrust. Part of the 25 percent will be converted to mechanical energy through the turbines to drive the fans. The other part will exit the exhaust section as kinetic energy.
75
25
BYPASS RATIO
The amount of air that bypasses the gas generator in comparison with the amount of air that passes through the gas generator is called the bypass ratio. This ratio ranges from about 1 to 5 or more
BRAYTON CYCLEA gas turbine engine follows a cycle of operation known as the Brayton Cycle. This operating cycle consists of four events which occur simultaneously:
INTAKE
COMPRESSION
COMBUSTION
EXHAUST
Highest pressure is after the________ before the burner
diffuser
Highest temperature is after the__________, before the turbine
burner
Highest velocity is after the ___________.
exhaust nozzle
The factors that affect the thrust of a gas turbine engine include
AIR DENSITY
AIRSPEED/RAM EFFECT
ENGINE RPM
If the density of air increases, mass will increase, and therefore thrust will _____________
INCREASE
As air temperature increases, air molecules tend to move apart. This results in a density decrease, and a resultant ___________ in thrust
DECREASE
As air pressure increases, air molecules tend to move closer together. This results in an increase in density, and therefore, thrust__________.
INCREASE
With an increase in altitude, however, the rate of thrust decreases because a pressure drop is greater than the thrust increase resulting from a temperature drop. This means an engine will produce _________ as it increases in altitude
less thrust
At approximately 36,000 feet (beginning of the isothermal layer), temperature stabilizes. As a result, temperature will no longer offset the density decrease due to pressure. Therefore, thrust decreases more rapidly. This altitude is also known as the _______________ At this altitude, thrust available plus low fuel flow and diminished drag combine to provide optimum performance for many engines
optimum cruise level.
One of the most obvious factors that affects the thrust output is the rotational speed of the engine. With an increase in RPM, there is an increase in thrust. However, at low RPM there is very little increase in thrust with an increase in throttle. At higher rates of revolution, a small increase in throttle setting will produce a_______ increase in thrust
large
At lower settings, fuel consumption is high for the amount of thrust produced. For this reason, gas turbine engines are normally operated at or near their __________ RPM
maximum
Engine Pressure Ratio (EPR): The EPR gauge indicates the pressure ratio between the ______________. The EPR gauge is more widely used because it automatically accounts for some of the airflow variations at the inlet
inlet and exhaust airflow
EGT (Exhaust Gas Temperature): Measured aft of the ________ section
turbine
TIT (Turbine Inlet Temperature): Temperature of the gases from the ________________ of the engine as they enter the first stage of the turbine
TIT is the highest temperature inside a turbine engine and is difficult to measure which is why EGT is often measured instead
combustion section
The primary function of the compressor:
- is to supply enough air to satisfy the requirements of the combustion section. Specifically, the compressor increases the pressure of the airflow from the air inlet duct and directs it to the burners in the quantity and at the pressures required.
- A secondary function is to supply compressor bleed air to operate various components throughout the engine and aircraft
Because the compressor section receives energy from the turbine via the drive shaft, it is not a closed system. Therefore, the increase in velocity will not result in a decrease in pressure. In fact, both velocity and pressure will increase in the compressor section and therefore, total ______________.
pressure increases
Axial flow compressor The term axial-flow applies to the axial (straight line) flow of air through the compressor section of the engine. An axial-flow compressor has two main elements: Rotor blades and stator vanes. Rotor blades are \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Stator vanes are \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_ Each rotor and stator pair forms a stage
rotating, airfoil shaped blades
stationary airfoil-shaped blades
Efficient use of multiple stages can produce very high overall ___________ ratios
compression
