aerodynamics seminar

7/21/2019 Aerodynamics Seminar

1/58

Aerodynamics 101

How do those things really fly?

Dr. Paul Kutler

Saturday, March 31, 2007

Monterey Airport


2/58

Airbus 380

An aerodynamics challenge


3/58

FA-18 Condensation Pattern

Aerodynamics involves multiple flow regimes


4/58

Legacy Aircraft

Aerodynamics is a maturing science


5/58

Outline

Terms and Definitions

Forces Acting on Airplane

Lift

DragConcluding remarks


6/58

Terms and Nomenclature

Airfoil Angle of attack

Angle of incidence

Aspect Ratio

Boundary Layer

Camber

Chord

Mean camber line

Pressure coefficient

Leading edge

Relative wind Reynolds Number

Thickness

Trailing edge

Wing planform

Wingspan


7/58

Force Diagram


8/58

Airfoil Definitions


9/58

Definition of Lift, Drag & Moment

L = 1/2 V2CLSD = 1/2 V2CDS

M = 1/2 V2CMS c


10/58

A Misconception

A fluid element that splits at the leading edge andtravels over and under the airfoil will meet at the

trailing edge.The distance traveled over the top is greater than over thebottom.

It must therefore travel faster over the top to meet at thetrailing edge.

According to Bernoullis equation, the pressure is lower onthe top than on the bottom.

Hence, lift is produced.


11/58

How Lift is Produced

Continuity equation

Bernoullis equation

Pressure differential

Lift is produced


12/58

The Truth

A fluid element moving over the top surface leavesthe trailing edge long before the fluid elementmoving over the bottom surface reaches the

trailing edge.

The two elements do not meet at the trailing edge.

This result has been validated both experimentallyand computationally.


13/58

Airfoil Lift Curve (clvs. )


14/58

Lift Curve - Cambered &Symmetric Airfoils


15/58

Slow Flight and Steep TurnsL = 1/2 V2CLS

Outcome versus Action

Slow Flight

Lift equals weightVelocity is decreased

CLmust increase

must be increased on the lift curve

Velocity can be reduced until CLmaxisreached

Beyond that, a stall results


16/58

Slow Flight and Steep TurnsL = 1/2 V2CLS

Outcome versus Action(Concluded)

Steep Turns (Bank, yank and crank)

Lift vector is rotated inward (bank) by the bankangle reducing the vertical component of lift

Lift equals weight divided by cosine

Either V (crank), CLor both must be increased to

replenish liftTo increase CL, increase (yank)on the lift curve

To increase V, give it some gas

More effective since lift is proportional to the velocity

squared


17/58

Stalling Airfoil


18/58

Effect of Bank Angle on StallSpeed

L = 1/2 V2CLS

equals the bank angle

At stall CLequals CLmaxL = W / cos ThusV

stall= [2 W / (C

L maxS cos )] 1/2

Airplane thus stalls at a higher speed

Load factor increases in a bankThus as load factor increases, Vstallincreases

This is whats taught in the Pilots Handbook


19/58

Effect of CG Location on StallSpeed


20/58

Surface Oil Flow - Grumman Yankee= 40,110 , &240


21/58

Airfoil Pressure Distribution

NACA 0012, M = 0.345, = 3.930


22/58

Supercritical Airfoil &Pressure Distribution


23/58

Drag of an Airfoil

D = Df+ Dp+ Dw

D = total drag on airfoilDf= skin friction drag

Dp= pressure drag due to

flow separationDw = wave drag (for transonic

and supersonic flows)


24/58

Skin Friction Drag

The flow at the surface of the airfoil adheres tothe surface (no-slip condition)

A boundary layer is created-a thin viscousregion near the airfoil surface

Friction of the air at the surface creates ashear stress

The velocity profile in the boundary layer goes

from zero at the wall to 99% of the free-stream value

= (dV/dy)wall

is the dynamic viscosity of air [3.73 (10) -7

sl/f/s]


25/58

The Boundary LayerTwo types of viscous flows

Laminar

Streamlines are smooth and regular

Fluid element moves smoothly along streamline

Produces less drag

TurbulentStreamlines break up

Fluid element moves in a random, irregular andtortuous fashion

Produces more dragw laminar< w turbulent

Reynolds Number

Rex= Vx /

Ratio of inertia to viscous forces

B d L Thi k


26/58

Boundary Layer Thickness(Flat Plate)

Laminar Flow= 5 x / Rex

1/2

Turbulent Flow= 0.16 x / Rex

1/7

Turbulent Flow-Tripped B.L.= 0.37 x / Rex

1/5

Example: Chord = 5 f, V= 150 MPH, Sea

LevelRex= 6,962,025

= 0.114 inches Laminar B.L.

= 1.011 inches Turbulent B.L.

= 7.049 inches Tripped Turbulent B.L.


27/58

Infinite vs. Finite Wings

AR = b2/ S


28/58

Finite Wings


29/58

The Origin of Downwash


30/58

The Origin of Induced Drag

Di= L sin i


31/58

Elliptical Lift Distribution

CD,I= CL2/ (e AR)


32/58

Change in Lift Curve Slope

for Finite Wings


33/58

Ground Effect

Occurs during landing and takeoff

Gives a feeling of floating or riding on acushion of air between wing and ground

In fact, there is no cushion of air

Its effect is to increase the lift of the wing andreduce the induced drag

The ground diminishes the strength of the wing

tip vortices and reduces the amount ofdownwash

The effective angle of attack is increased andlift increases

G o nd Effect


34/58

Ground Effect(Concluded)

Mathematically SpeakingL= 1/2

V

2S CL

An increased angle of attack, increases CL

Hence L is increased

D= 1/2 V

2S [CD,0+ CL2/(e AR)]

CD,0is the zero lift drag (parasite)

CL2/(e AR)is the induced drag

e is the span efficiency factor = (16 h / b)2/ [1 + (16 h / b)2]

b is the wingspan

h is the height of the wing above the ground


35/58

Wing Dihedral ()

Wings are bent upwardthrough an angle , calledthe dihedral angle

Dihedral provides lateralstability, i.e., an airplane ina bank will return to itsequilibrium position

This is a result of the lift onthe higher wing being lessthan the lift on the lowerwing providing a restoringrolling moment


36/58

Drag of a Finite Wing

D = Df+ Dp+ Dw + Di

D = total drag on wing

Df= skin friction dragDp= pressure drag due to

flow separation

Dw = wave drag (for transonicand supersonic flows)

Di= Induced drag (drag due to

lift)


37/58

Drag of a Wing

(Continued)

Induced drag - drag due tolift

Parasite drag - drag due tonon-lifting surfacesProfile drag

Skin frictionPressure drag (Form drag)

Interference drag (e.g., wing-fuselage, wing-pylon)

Flaps


38/58

FlapsA Mechanism for High Lift


39/58

Effect of Flaps on Lift Curve

High Lift Devices


40/58

High Lift Devices

1. No flap2. Plain flap3. Split flap4. L. E. slat5. Single slotted flap

6. Double-slotted flap7. Double-slotted flap

with slat8. Double-slotted flap

with slat andboundary layersuction

9. Not shown - Fowlerflap


41/58

Shape Comparison

Modern vs. Conventional Airfoils


42/58

Maximum Lift Coefficient ComparisonModern vs. Conventional Airfoils


43/58

Whats Next on the AgendaBoeing 787 Dreamliner

Boeing 787


44/58

Whats Next on the Agenda

Boeing Blended Wing-Body Configuration

Boeing 797


45/58

Concluding Remarks

What was not discussedTransonic flow

Drag-divergence Mach numberSupersonic flow

Wave drag

Swept wings

Compressibility effectsBoundary layer theory

The history of aerodynamics

b


46/58

Airbus 380 Interior

Good aerodynamics results in improved creature comforts

Q i d


47/58

Questions and Answers


48/58

Backup Slides

Wi l t


49/58

WingletsReduced induced drag

Equivalent to extendingwingspan 1/2 of wingletheight

Less wing bending momentand less wing weight thanextending wing

Hinders spanwise flow and

pressure drop at the wingtip

Looks modern/esthetically

pleasing

Boeing 737 Winglet

V t G t


50/58

Vortex Generators


51/58

Swept-Wing Principle


52/58

Wave Drag

H d J t


53/58

HondaJet


54/58

HondaJet

Engine Position

The Sweet SpotLocation where the engine coexists with the wing

and enjoys favorable interference effects

The reason -Transonic Area RuleRichard Whitcomb - NASA Scientist

The total cross-sectional area must vary smoothlyfrom the nose to tail to minimize the wave drag

Wave drag is created by shock waves that appearover the aircraft as a result of local regions of

embedded supersonic flow

HondaJet


55/58

HondaJetAerodynamics

Engine inlet is positioned at 75% chordAs the cross-sectional area decreases at the trailing

edge of the wing, the engine adds area thusyielding a smooth area variation

This engine position also slows the flow anddecreases the wing-shock strength

The critical Mach number is thus increased from.70 to .73

The pylon is positioned near the outer portion ofthe nacelle and cambered inward to follow the flowdirection

During stall, separation starts outboard of thepylon; separation does not occur between the

lon and fusela e


56/58

HondaJet

Aerodynamics(Continued)

Natural laminar flow fuselage nose

Following the area rule, the nose expandsfrom its tip and then contracts as the

windshield emerges.As the wing is approached, the fuselage

cross-sectional area increases smoothly;

this helps maintain the laminar flow


57/58

HondaJet

Aerodynamics(Concluded)

Natural laminar flow wing

Utilizes integral, machined panels that

minimizes the number of parts for smootherflow when mated together

Employs winglets to reduce induced drag

30% more efficient than other business jets

E l i Fli ht


58/58

Eagle in Flight

Winglets

Elastic Flaps

Minimized Noise& Detectability

Variable

Camber

Retractable Landing Gear

STOL/VTOLCapabilities

Smart Structures

Tilting

Control

CenterSmooth

Fairings

Variable

Twist

Adaptive

Dihedral

Turbulator

Tail ?

b/2

c

cd,i= cl2/

AR

cl= 2 L/V2S

aerodynamics seminar

Documents