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

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

Historical Airfoils

Historical Airfoils

Typical Streamlines Angle of Attack

Pressure Distribution

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.

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

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

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

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

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

Resultant Aerodynamic Force

Lift & Drag Coefficients

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

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

Open-Circuit Wind Tunnel

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.

Closed-Circuit Wind Tunnel

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

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

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.

Stalled Airfoil

Reynolds Number Effect

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:

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

Typical Cambered Airfoil NACA 2412 Lift Curve & Drag Polar

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) 0.7/0.0076 = 92.1 1.0/0.0088 = 113

Computation Fluid Dynamics Simulation

CFD Simulation: Near stall

CFD Simulation: Fully Stalled

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

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