5-1 Principles of Gas Turbine Operation

• 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.

• An opening that increases the airflow's velocity and decreases the airflow's pressure.
• Subsonic air - Convergent passage
• Supersonic air - divergent passage

• An opening that causes pressure to increase and velocity to decrease.
• Subsonic-Divergent passage
• Supersonic-Convergent

• 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

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• 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.

• 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.
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• Net thrust and gross thrust will be equal when inlet airflow velocity is zero and the atmospheric conditions are standard.

• Air Density
• Increase in Density =increase Mass = Increase thrust

• Temperature
• Increase in Temperature

• The compressibility of airflow as velocity increases toward supersonic.
• Typically, as airspeed increases, thrust decreases.
• Net thrust = mass * (V_final-V_initial)/t 
• Sincer higher airspeed increases V_initial 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.

• 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).