Flow over an airfoil

Aim: To study the Flow simulation over a NACA airfoil at different angles of attack.

Objective:

• Calculate the drag force and lift force
• Compare the drag force with varying angles of attack.
• Compare the lift force with the angle of attack.

Theory:

An aerofoil is the cross-sectional shape of a wing, blade (of a propeller, rotor, or turbine), or sail (as seen in cross-section).

An aerofoil-shaped body moving through a Liquid produces an aerodynamic force. The component of this force perpendicular to the direction of motion is called lift. The component parallel to the direction of motion is called drag. subsonic Fight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with asymmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the working fluid are called hydrofoils.

The lift on an airfoil is primarily the result of its angle of attack. When oriented at a suitable angle, the airfoil deflects the oncoming air (for Fixed-wing aircraft, a downward force), resulting in a force on the airfoil in the direction opposite to the de direction.

The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics(NACA). The shape of the NACA airfoils is described using a series of digits following the word "NACA". The parameters in the numerical code can be entered into equations to precisely generate the cross-section of the airfoil and calculate its properties.

The NACA four-digit wing sections define the profile by:

1. First digit describing maximum camber as a percentage of the chord.
2. The second digit describing the distance of maximum camber from the airfoil leading edge in tenths of the chord.
3. Last two digits describing the maximum thickness of the airfoil as a percent of the chord.

For example, the NACA 2412 airfoil has a maximum camber of 2% located 40% (0.4 chords) from the leading edge with a maximum thickness of 12% of the chord. The NACA 0015 airfoil is symmetrical, the 00 indicating that it has no camber. The 15 indicates that the airfoil has a 15% thickness to chord length ratio: it is 15% as thick as it is long.

Parameters:

• Flow Simulation = External
• Pressure = 101325 Pa
• Temperature = 293.2 K
• Velocity along x-axis = 600 m/s
• Medium = Air
• Time-dependent study

Problem statement:

1. Model the flow over a NACA0017 airfoil
2. For the angle of attacks 0,2,4,6,8,10 compare the lift and drag forces

Steps:

1. Insert the NACA airfoil .txt file from the airfoil database provided.
2. Sketch the airfoil by connecting the ends
3. Extrude the airfoil and save it.
4. Activate the flow simulation and add the parameters in the wizard command.
5. Select the 2D computational domain and increase the domain size
6. Edit the global mesh and local mesh at the face of the curve for refinement.
7. Set surface goals to get the drag and lift force.
8. Run the simulation
9. Insert plots of pressure and velocity
10. Insert goals from results to get drag and lift force results.

Result:

At zero angle of attack

NACA airfoil 3d Model:

Velocity distribution

Pressure distribution

At 2 degree angle of attack

NACA airfoil 3d Model at a 2-degree angle of attack:

Velocity distribution

Pressure distribution

At 4 degree angle of attack

NACA airfoil 3d Model at a 4-degree angle of attack:

Velocity distribution

Pressure distribution

At 6 degree angle of attack

NACA airfoil 3d Model at a 6-degree angle of attack:

Velocity distribution

Pressure distribution

At 8 degree angle of attack

NACA airfoil 3d Model at an 8-degree angle of attack:

Velocity distribution

Pressure distribution

At 10 degree angle of attack

NACA airfoil 3d Model at a 10-degree angle of attack:

Velocity distribution

Pressure distribution

Drag force and lift force for the various angle of attack is given in below table,

Observations:
		Drag force in Newton
Angle of attack			Lift force in Newton (average)
		(average)
0		316.1	0.66
2		323.8	830.45
4		434.21	1672.36
6		554.79	2501.25
8		752.033	3245.12
10		998.53	4014.98

Plots obtained:

The plot of Angle of attack vs drag force

The plot of the angle of attack vs lift force

The plot of Drag force vs lift force

Conclusion

1. Drag force increases slowly with an increase in the angle of attack and lifts force increases rapidly with an increase in the angle of attack.
2. At zero degree angle of attack, the lift is found to be zero due to the symmetry of airfoil.
3. As the angle of attack increases the lift force also increases and the size of the wake region also increases.
4. The blue light increases below the airfoil in the pressure plot as the angle of attack is increased as pressure increases in that region.
5. With an increase in the angle of attack, the velocity of air over airfoil increases.
6. Similarly, as the velocity flows over the airfoil more than the lower region the pressure under it decreases this creates suction and causes lift.