ME403 Chapter 2

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ME403 Chapter 2 2D Airfoil Aerodynamics
Lift is mainly provided by the wing with an
airfoil cross-section shape
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Airfoil Geometry
An airfoil is the 2D cross-section shape of the
wing, which creates significant lift but minimal
drag because of this aerodynamic shape
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Historical Airfoils
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Historical Airfoils
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Typical Streamlines
Angle of Attack
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Pressure Distribution
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Pressure Coefficient Distribution
In the uniform free-stream
At the stagnation point (at which velocity V0)
Positive Cp means the pressure is higher than the
free-stream (atmospheric) pressure, and negative
Cp means suction relative to free-stream
pressure. The maximum, which occurs at the
stagnation point, is always 1.
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Viscous Boundary Layer
Velocity profile creates skin friction (shear)
drag on surface
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Flat Plate Skin Friction Drag Coefficient
Curve fit formula for turbulent boundary layer
(Re gt 500,000)
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Evolution of Airfoil Design
Delaying transition point from Laminar to
Turbulent boundary layer reduces skin friction
drag
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Boundary Layer Flow Separation
When flow separation occurs, there is also
pressure drag.
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Pressure (Form) Drag due to Flow Separation
100 Pressure Drag
Total Profile Drag Skin Friction Drag Form
Drag
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Resultant Aerodynamic Force
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Lift Drag Coefficients

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Center of Pressure
The resultant aerodynamic force acts at the
Center of Pressure (c.p.), about which the moment
is zero.
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Open-Circuit Wind Tunnel
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Wind Tunnel Tests
Force transducer behind model senses lift, drag
and pitching moment directly. Motor-controlled
mechanism adjusts the models angle of attack.
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Closed-Circuit Wind Tunnel
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Wing Section Models
Model for measuring lift, drag and pitching moment
Model for measuring surface pressure distribution
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NACA 0006 Data at Re 3,180,000
There is a maximum Lift-to-Drag ratio
(L/D). Location of Center of Pressure (c.p.)
varies with a
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NACA 2312 Data at Re 3,120,000
Lift decreases and drag increases sharply beyond
the stall (max. Cl) point, due to boundary layer
separation.
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NACA Airfoils and Test Data
4-Digit Series 5-Digit Series 6
Series http//naca.larc.nasa.gov/reports/1945/nac
a-report-824/
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Stalled Airfoil
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Reynolds Number Effect
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Aerodynamic Center
Since the c.p. varies with a, it is more
desirable to use a fixed Aerodynamic Center
(a.c.) as the point of action of the lift and
drag. The pitching moment about this point can
be calculated, and is found insensitive to a.
For most airfoils, the a.c. locates at around
quarter chord (xc/4).
Pitching Moment Coefficient
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Typical Non-Cambered AirfoilLift Curve Drag
PolarNACA 0006
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Typical Cambered AirfoilNACA 2412 Lift Curve
Drag Polar
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Typical Airfoil Aerodynamic Characteristicsat Re
6 million
NACA 0006 NACA 2412
Zero-Lift Angle of Attack (deg.) 0 -2
Stall Angle of Attack (deg.) 9 16
Maximum Lift Coefficient 0.9 1.7
Lift Curve Slope (/deg.) 0.1 0.108
Moment Coefficient (before stall) 0 -0.05 to -0.02
Minimum Drag Coefficient 0.005 0.006
Max. Lift-to-Drag Ratio (L/D) 0.7/0.0076 92.1 1.0/0.0088 113
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Computation Fluid Dynamics Simulation
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CFD Simulation Near stall
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CFD Simulation Fully Stalled
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Airfoil Generator at http//www.ae.su.oz.au/aero/i
nfo/index.html
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Airfoil Analysis Code at http//www.ae.su.oz.au/ae
ro/info/index.html