Gas turbine engines Flashcards
gas turbine components
compressor, combustion chamber, turbine. components
compressor
draws in air and compresses it
combustion chamber
fuel pumped in and ignited burning compressed air
turbine
hot gasses converted to work. drives compressor and external load
radial flow compressors
Pros: simple design, not as expensive, good for low compression ratios.
Cons: difficult to stage, less efficient
axial flow compressors
Pros: most common, more compact, has multi-stage high compression ratios, more efficient
cons: expensive, vulnerable to foreign object debris/damage (FOD) via intakes
compressed air usage
primary (30%) secondary air (65%) film cooling air (5%)
primary air
passes directly to combustor for combustion process. 30%
secondary air
passes through perforated holes of inner shell & mixes with combustion gasses. cools gassesfrom the combustor to the turbine. prevents heating damage to the turbine. 60%
film cooling air
insulates /cool turbine blades. 5%
CAN combustion chamber type
centrifugal compressor
ANNULAR combustion chamber type
larger, axial compressors (LM2500)
CAN-ANNULAR combustion chamber type
smaller gas turbine engines
gas turbines
converts kinetic energy of hot combustion gas to rotational energy. Uses vanes (nozzles) and blades similar to the turbine. drives the compressor and an external load. self-sustaining after start-up
starter
on accessory gear box. process sequence: rotate compressor shaft using compressed air, fuel injected into combustor, electric spark provides initial ignition, combustion self sustaining after start
auxiliaries
on accessory gear box. essential systems for operation: lube oil, fuel pump, generator (some platforms)
Brayton cycle
intake, compression, combustion, expansion, exhaust. cycle
GTE advantages
can burn two types of fuel, greater fuel efficiency (compared to diesels), high reliability (GTE on ships are from planes), less vibration, little or no cooling water required, power-to-weight ratio, quicker response time (faster acceleration/deceleration), rapid start time, reduced manning requirements
GTE disadvantages
many components cannot be repaired in place (diesel repaired on deployment), do not do well in sandy/high salt areas, high pitched noise, inefficient at low or partial loads, large quantities of hot exhaust (huge IR target) new stacks cool exhaust, many parts under high stress, need large quantities of air
single shaft design
power coupling on same shaft as turbine, same shaft drives compressor rotor and engine power components.
Efficiently operates at constant speeds, maintains fairly constant load , no rpm changes needed
split shaft design
gas generator turbine drives compressor. a separate power turbine, driven by exhaust from gas generator turbine, drives the power coupling
used in propulsion, GTE is AERODYNAMICALLY coupled to power turbine NOT mechanically both turbines operate AT INDEPENDENTLY efficient speeds
changing speed controllable pitch GTE
prop blade pitch, lower speed changes 0-13(5) knots (at the pier), shaft RPM higher speed changes typically 13-30+
turboshaft
rotors driven entirely by power turbine, no thrust from engine exhaust. MH-60 seahawk and MH-53 sea stallion
turboprop
single shaft, turbine drives propeller thru gearbox. some additional thrust from engine exhaust. P-3 ORION, C-2 GREYHOUND, E-2 HAWKEYE
turbojet
thrust achieved solely through exhaust. ex: mid range missiles, variations of Tomahawk cruise missiles
turbofan
thrust from engine exhaust, additional thrust from fan. More efficient than turbojet in most application. F/A -18 HORNET, EA-18 GROWLER, joint strike (JSF) & poseidon
