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Introduction to AERODYNAMICS

Aerodynamics is an applied science to learn:

• External flow: the prediction of forces and moments on, and heat transfer to, bodies moving through a fluid.

- Aerodynamic forces (lift, drag), moments and center of pressure on flying objects (airfoil, airplanes, birds)

- Wind forces on wind turbine, building (bridge), sports (bicycle, baseball)

- Hydrodynamic forces on ships, submarines, torpedoes, swimmers.

- Aerodynamic heating of space vehicle, reentry of the space shuttle.

• Internal flow: determine flow moving internal through ducts.

- Jet engine inlets.

- Turbomachinery in air-breathing jet engines or turbine power generator.

- Exhaust nozzles and thrust of propulsion

AERODYNAMIC FORCES AND MOMENTS (I)

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AERODYNAMIC FORCES AND MOMENTS (II)

Forces:On upper surface

On lower surface

Moments about leading edge:

Aerodynamic Coefficients (CL, CD, CM/ Cl, Cd, Cm)For 3-D finite wing:

For 2-D airfoil:

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In Class Practice

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CENTER OF PRESSURE

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In Class HW#2

TYPES OF FLOW (II)

Kn << 1

Lh stic lengtCharacteri

pathfreemeanKn

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Viscosity of Fluid

dy

du

A

Fstressshear There is viscosity () of fluid

http://www.youtube.com/watch?v=cUTkqZeiMow

No-Slip Condition at the boundary: the fluid in direct contact with the solid boundary has the same velocity of the boundary.

TYPES OF FLOW (II)

Viscous v.s. Inviscid Flow:

Reynolds number:

UL

Re

• Re -> => inviscid flow

• GeometryFlow outside the boundary layer is inviscid.

Thin boundary layer of viscous flow adjacent to surface. Flow separation (viscous effect)

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Aerodynamic Forces of Incompressible and Viscous Flow over Thin Airfoil (θ<<1) with small Angle of Attack (α<<1)

cossincos NANL

coscossin AAND

Lift force can be estimated very good even assuming inviscid.

Drag force can not get good estimation by only assuming inviscid.

TYPES OF FLOW (III)

viscosity =0

Kn << 1

Lh stic lengtCharacteri

pathfreemeanKn

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Incompressible v.s. Compressible Flow:

speed) (

velocity)(

soundc

UM

Mach number:

M<0.3 Incompressible Flows

=> fluid is treated as incompressible

M>0.3 Compressible Flows

=> fluid is treated as compressible

Subsonic, Transonic and Supersonic Flows

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Supersonic Wind Tunnel

TYPES OF FLOW (III)

M<0.3

0.3<M<0.8 0.8<M<1.2 1.2<M<5 M>5

viscosity =0

Kn << 1

0

dy

du

stressshear

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AERODYNAMIC FORCES AND MOMENTS of Incompressible and Invicid Flow

Lift force can be estimated very good even assuming inviscid.

Drag force can not get good estimation by only assuming inviscid.

ROADMAP FOR AERODYNAMICS

SUBSONIC FLOW (incompressible , inviscid flow)

BASIC AERODYNAMICS TOOLS (Basic Governing Equations)

TRANSONIC/SUPERSONIC FLOW (compressible, inviscid flow)

Potential flow (irrotational flow)

2D airfoil (thin airfoil theory)

3D finite wing (lifting line theory)

Supersonic airfoil (shock expansion method)

Normal/oblique shock (Prandtl-Meyer function)

Method of characteristics