Introduction to Gas Turbines Flashcards
Thrust = Mass Formula
Thurst = Mass x (Vjet - Vair)
How is thrust produced in a basic turbine engine?
Thrust is produced by accelerating a mass of air backwards.
There will be an opposite and equal reaction to this.
Relationship between thrust and power with increasing forward speed?
Thrust is constant within subsonic range.
Power will decay after reaching a maximum forward speed.
Thermal Efficiency
Fuel is converted to kinetic energy. Around 30%.
Propulsive Efficiency
Converting kinetic energy to propulsive energy. ~80-90%
Up to what speed may turboprops be more efficient than jet engines?
300kts.
How are today’s jet engines 10x more capable of thrust
Higher bypass ratios - mass of air flows at a greater speed with higher turbine temperatures.
Repercussions of exceeding engine limitations
Shockwaves of air get spilled out, compromising engine life and reliability.
Brayton Cycle
Compression
Combustion
Expansion
Exhaust
Where are the highest gas temperatures found?
Combustion
Flat Rating
Power limited to a set level by RPM up to a certain temperature.
Over ISA +15C, becomes temperature limited
Twin Spool Bypass
0.8:1 compression ratio.
Some air bypassed around hot core (centre), rest flows through HP compressor. Spins faster with greater compression.
Where do the LP compressor and HP compressors work most efficiently?
LP Compressor - low speeds
HP Compressor - high speeds
Separately.
Twin Spool High Bypass
70% of Air comes from bypass air. 5:1 Bypass Ratio, 5 parts of air bypassed, 1 through the centre.
How do turboprops drive a propeller?
Via a reduction gearbox.`
