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EXPLAIN Bernoulli's Equation, given dynamic pressure, static pressure, and total pressure
- Bernoulli's Equation
- Total Pressure =Static Pressure+Dynamic
- TP = Pressure + Velocity
Bernoulli's theorem states that an any incompressible fluid passes through a convergent opening, its velocity increases and pressure decreases.
For total pressure, if pressure (static pressure) increases, velocity (dynamic pressure) must decrease.
DESCRIBE the behavior of airflow in a nozzle
- An opening that increases the airflow's velocity and decreases the airflow's pressure.
- Subsonic air - Convergent passage
- Supersonic air - divergent passage
DESCRIBE the behavior of airflow in a diffuser
- An opening that causes pressure to increase and velocity to decrease.
- Subsonic-Divergent passage
DESCRIBE the Brayton Cycle
- Consist of 4 cycles that simultaneously occur.
- Very different than the operating cycle of a reciprocating engine (Otto cycle).
- -Brayton cycle occurs simultaneously, Otto cycle occurs sequentially
- -Brayton cycle takes place throughout the gas turbine engine, Otto cycle generally takes place within a single piston
DESCRIBE a gas generator
- Produces the high-energy airflow necessary for creating thrust.
- It will minimally include the compressor, combustion chamber, and turbine.
- Turbofan, turboprop, and turboshaft will include their respective fan, propeller or rotor blades.
DESCRIBE how airflow properties change through each section of a gas turbine engine
DESCRIBE engine thrust
- The result of many pressure, temperature, and velocity changes as airflow passes through an engine
- Gross thrust is the measurement of thrust due solely from the velocity of the exhaust gas (such as the engine being mounted and tested)
- Net Thrust is Gross thrust corrected for the effect of inlet airflow velocity.
- Net thrust and gross thrust will be equal when inlet airflow velocity is zero and the atmospheric conditions are standard.
DESCRIBE the effects of airflow properties on thrust in a gas turbine engine
- Air Density
- Increase in Density =increase Mass = Increase thrust
- Increase in Temperature
EXPLAIN ram effect in a gas turbine engine
- The compressibility of airflow as velocity increases toward supersonic.
- Typically, as airspeed increases, thrust decreases.
- Net thrust = mass * (Vfinal-Vinitial)/t
- Sincer higher airspeed increases Vinitial thrust decreases.
- However, the higher airspeed causes air to be "rammed" into the inlet, increasing the mass and pressure.
- This offsets the decrease in acceleration and results in a neutral effect or slight increase in thrust at subsonic airspeeds.
DESCRIBE the cockpit thrust measuring devices
- Pressure Indication Gauges
- For aircraft that rely on the propulsive power of the exhaust gas turbine engine, such as turbojets and turbofans, use a Engine Pressure Ratio (EPR) gauge.
- The EPR indicates the pressure ratio between the inlet and exhaust airflow.
- It is more widely used because it automatically accounts for some of the airflow variations at the inlet (thrust available).
- Used by a turboprop or turborotor to indicate power available.
- Indicates shaft horsepower available to drive a propeller or rotor.
- Gauge most commonly used to determine engine performance.
- Provides crew with an indication of engine speed.
- Does not actually measure thrust, but gives a quick assessment of energy produce by the engine
- Uses percent rpm (most engines 100% represents full power).