5-1 Principles of Gas Turbine Operation

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  1. 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.
  2. 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
  3. DESCRIBE the behavior of airflow in a diffuser
    • An opening that causes pressure to increase and velocity to decrease.
    • Subsonic-Divergent passage
    • Supersonic-Convergent
  4. DESCRIBE the Brayton Cycle
    • Consist of 4 cycles that simultaneously occur.
    • Intake
    • Compression
    • Combustion
    • Exhaust

    • 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
  5. DESCRIBE a gas generator
    • Image Upload
    • 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.
  6. DESCRIBE how airflow properties change through each section of a gas turbine engine
    Image Upload
  7. 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.
    • chart?chf=bg,s,00000000&cht=tx&chl=Net%20Thrust%3Dm%5Ccdot%5Cfrac%7BV_%7BFinal%7D-V_%7BInitial%7D%7D%7Bt%7D&chs=480x70
    • Net thrust and gross thrust will be equal when inlet airflow velocity is zero and the atmospheric conditions are standard.
  8. DESCRIBE the effects of airflow properties on thrust in a gas turbine engine
    • Air Density
    • Increase in Density =increase Mass = Increase thrust

    • Temperature
    • Increase in Temperature
  9. 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.
  10. 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).

    • Torquemeter
    • Used by a turboprop or turborotor to indicate power available.
    • Indicates shaft horsepower available to drive a propeller or rotor.

    • Tachometer
    • 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).
Card Set:
5-1 Principles of Gas Turbine Operation
2016-06-05 00:37:19
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