ppt jet.ppt

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.