1. 2D Airfoil Aerodynamics
ME403 Chapter 2
2D Airfoil Aerodynamics
Lift is mainly provided by the wing with an airfoil cross-section shape

2. Airfoil Geometry
An airfoil is the 2D cross-section shape of the wing, which creates sufficient lift with minimal drag

3. Historical Airfoils

4. Historical Airfoils

5. Typical Streamlines
Angle of Attack

6. Pressure Distribution

7. Pressure Coefficient Distribution At stagnation point (V=0):
In free-stream:
At stagnation point (V=0):
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.

8. Viscous Boundary Layer
Velocity profile creates skin friction (shear) drag on surface

9. Flat Plate Skin Friction Drag Coefficient
Curve fit formula for turbulent boundary layer (Re > 500,000):

10. Evolution of Airfoil Design
Laminar boundary layer creates less skin friction drag

11. Boundary Layer Flow Separation
When flow separation occurs,
there is also pressure drag.

12. Pressure (Form) Drag due to Flow Separation
100% Pressure Drag
Total Profile Drag
= Skin Friction Drag
+ Form Drag

13. Resultant Aerodynamic Force

14. Lift & Drag Coefficients

15. Center of Pressure
The resultant aerodynamic force acts at the Center of Pressure (c.p.), about which the moment is zero.

16. NACA Airfoils and Test Data
4-Digit Series
5-Digit Series
6 Series

17. Open-Circuit Wind Tunnel

18. Motor-controlled mechanism adjusts the model’s angle of attack.
Wind Tunnel Tests
Force transducer behind model senses lift, drag and pitching moment directly.
Motor-controlled mechanism adjusts the model’s angle of attack.

19. Closed-Circuit Wind Tunnel

20. Wing Section Models Model for measuring lift, drag and pitching moment
Model for measuring surface pressure distribution

21. 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

22. 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.

23. Stalled Airfoil

24. Reynolds Number Effect

25. Pitching Moment Coefficient:
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 (x=c/4).
Pitching Moment Coefficient:

26. Typical Non-Cambered Airfoil Lift Curve & Drag Polar NACA 0006

27. Typical Cambered Airfoil NACA 2412 Lift Curve & Drag Polar

28. Airfoil Aerodynamic Characteristics at Re = 6 million
NACA 0006
NACA 2412
Zero-Lift Angle of Attack (deg.) -2
Stall Angle of Attack (deg.) 9 16
Maximum Lift Coefficient
0.9
1.7
Lift Curve Slope (1/deg.)
0.1
0.108
Moment Coefficient (before stall)
0.05
Minimum Drag Coefficient
0.005
0.006
Max. Lift-to-Drag Ratio (L/D)
0.7/ = 92.1
1.0/ = 113

29. Computation Fluid Dynamics Simulation

30. CFD Simulation: Near stall

31. CFD Simulation: Fully Stalled

32. Airfoil Generator at http://www.ae.su.oz.au/aero/info/index.html

33. Airfoil Analysis Code at http://www.ae.su.oz.au/aero/info/index.html