Gas Turbine Engine Theory Flashcards

What happens to gas velocity and pressure as subsonic gas flows through a convergent exhaust nozzle?

Answer: Velocity increases, pressure decreases

Per Bernoulli's principle, subsonic flow in a convergent duct accelerates while static pressure drops.

A choked exhaust nozzle produces which type of additional thrust?

Answer: Pressure thrust

When the nozzle is choked, exit pressure exceeds ambient, and the pressure difference across the exit area adds pressure thrust.

Using F = M x (V2 - V1), what happens to net thrust as aircraft forward speed increases, assuming constant exhaust velocity and mass flow?

Answer: Net thrust decreases

Higher forward speed increases inlet velocity V1, reducing the velocity change and thus net thrust.

What is the purpose of a convergent-divergent exhaust nozzle on supersonic aircraft?

Answer: Allow exhaust gases to expand to supersonic velocity for added thrust

Flow reaches Mach 1 at the throat and accelerates supersonically in the divergent section.

Which engine parameter is generally used as the primary thrust-setting indication on many turbofan engines?

Answer: EPR or N1

EPR (exhaust pressure ratio) or fan speed N1 directly relates to thrust and is used for power setting.

Thrust specific fuel consumption (TSFC) is defined as which of the following?

Answer: Fuel flow per hour divided by thrust

TSFC is pounds of fuel burned per hour for each pound of thrust produced.

How does a cascade-type thrust reverser on a high-bypass turbofan produce reverse thrust?

Answer: By blocking the fan duct and directing bypass air forward through cascade vanes

Blocker doors obstruct the bypass duct and cascade vanes turn the air forward.