Transcript
Introduction to Jet Propulsion
P M V SubbaraoProfessor
Mechanical Engineering Department
Strong and Reliable Muscles for the Aircraft……
Global Momentum Analysis
Momentum Equation
pinlet
pexit
Vac Vjet
dt
dMF cm
surface
Reynolds Transport Theorem:
inletexitcvcm MM
dt
dM
dt
dM
Newton’s Second Law of Motion
inletexitcv
surface MMdt
dMF
For a frictionless flight, pressure forces are only the surface forces…
inletexitcv
ductwallexitexitinletinlet MMdt
dMFApAp
Steady state steady flow
inletexitductwallexitexitinletinlet MMFApAp
airairjetjetductwallexitexitinletinlet VmVmFApAp
airairjetjetexitexitinletinletductwall VmVmApApF
airairjetjetexitexitinletinletductwall VmVmApApF
Pressure Thrust Momentum Thrust
At design cruising conditions : Pressure thrust is zero.
airairjetjetthrust VmVmF
atmexitinlet ppp
Generation of Thrust : The Capacity
acairjetjetT VmVmF Thrust
acairjetfuelairT VmVmmF
acjetairT VVfmF 1
f : Fuel-air ratio
Dynamic Equilibrium : Cruising Vehicle
For a cruising vehicle:
Vehicleon 1 dragVVfmF acjetairT
2
12
airac
acdragacjetair
VACVVfm
Drag on Aircraft
Generation of Lift
Drag Coefficient of an Air Craft
Generation of Lift
Drag Coefficient of an Air Craft
Lift - to - Drag Ratio
Flight article Scenario L/D ratio
Virgin Atlantic GlobalFlyer
Cruise 37[
Lockheed U-2 Cruise ~28
Rutan Voyager Cruise[4] 27
Albatross 20
Boeing 747 Cruise 17
Common tern 12
Herring gull 10
Concorde M2 Cruise 7.14
Cessna 150 Cruise 7
Concorde Approach 4.35
House sparrow 4
Minimum Drag Coefficients Aircraft Type Aspect Ratio CDmin
RQ-2 Pioneer Single piston-engine UAV 9.39 0.0600 North American Navion Single piston-engine general aviation 6.20 0.0510
Cessna 172/182 Single piston-engine general aviation 7.40 0.0270
Cessna 310 Twin piston-engine general aviation 7.78 0.0270
Marchetti S-211 Single jet-engine military trainer 5.09 0.0205
Cessna T-37 Twin jet-engine military trainer 6.28 0.0200
Beech 99 Twin turboprop commuter 7.56 0.0270
Cessna 620 Four piston-engine transport 8.93 0.0322
Learjet 24 Twin jet-engine business jet 5.03 0.0216
Lockheed Jetstar Four jet-engine business jet 5.33 0.0126
F-104 Starfighter Single jet-engine fighter 2.45 0.0480 F-4 Phantom II Twin jet-engine fighter 2.83 0.0205 (subsonic)
0.0439 (supersonic)
Lightning Twin jet-engine fighter 2.52 0.0200 Convair 880 Four jet-engine airliner 7.20 0.0240
Douglas DC-8 Four jet-engine airliner 7.79 0.0188
Boeing 747 Four jet-engine airliner 6.98 0.0305
X-15 Hypersonic research plane 2.50 0.0950
Propulsive Power or Thrust Power:
acjetairacacTp VVfmVVFP 1
Specific Thrust S
acjetair
T VVfm
FS 1
Measure of compactness of a jet engine:
Thrust Specific Fuel Consumption TSFC
acjetacjetair
fuel
T
fuel
VVf
f
VVfm
m
F
mTSFC
11
Measure of fuel economy:
Aviation Appreciation
Propulsion Efficiency
Jet theofPower Kinetic Available
PowerThrustpropulsion
2212 acjetair
acTpropulsion
VVfm
VF
22)1(
2
1
acjetair
acacjetairpropulsion
VVfm
VVVfm
Jet Characteristics
• Quantities defining a jet are:
– cross-sectional area;
– composition;
– velocity.
jetjetjetjet VAm
acairjetjetjetT VmVAF 2
acairjetjetT VmVmF
Of these, only the velocity is a truly characteristic feature and is of considerable quantitative significance.
Jet Characteristics of Practical Propulsion Systems
System Jet Velocity (m/s)
Turbofan 200 - 600
Turbojet (sea-level, static) 350 - 600
Turbojet (Mach 2 at 36000 ft) 900 - 1200
Ramjet (Mach 2 at 36000 ft) 900 - 1200
Ramjet (Mach 4 at 36000 ft) 1800 - 2400
Solid Rocket 1500 – 2600
Liquid Rocket 2000 – 3500
Nozzle : Steady State Steady Flow
First Law :
No heat transfer and no work transfer & No Change in potential energy.
in jet
cv
jetin
cv WgzV
hmgzV
hmQ
22
22
jetin
Vh
Vh
22
22
Combined analysis of conservation of mass and first law
22
jetjet
jetinin
in A
mh
A
mh
A SSSF of gas through variable area duct can interchange the enthalpy and kinetic energy as per above equation.
Consider gas as an ideal and calorically perfect.
0
22
22Tc
c
VTc
c
VTc p
p
jetjetp
p
ininp
1
jet
in
jet
in
p
p
T
T
Isentropic expansion of an ideal and calorically perfect gas.
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