Flow over an airfoil

AIM: Simulate the flow over NACA Airfoil.

OBJECTIVES:

• Flow simulate over airfoil or the angle of attacks 0,2,4,6,8,10.
• Compare the lift and drag forces.

AIR FOIL

Airfoil is the cross-sectional shape of a wing, blade (of a propeller, rotor, or turbine), or sail (as seen in cross-section). An airfoil-shaped body moving through a fluid 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.

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 resulting in a force on the airfoil in the direction opposite to the deflection. This force is known as aerodynamic force and can be resolved into two components: lift and drag. Most foil shapes require a positive angle of attack to generate lift.

NACA AIRFOIL

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

I choose NACA 0024 airfoil for simulation means the 00 indicating that it has no camber. So, airfoil is symmetrical. The 24 indicates that the airfoil has a 24% thickness to chord length ratio: it is 24% as thick as it is long.

Procedure

1. Copy the Airfoil Coordinates from Airfoil Database .txt file.
2. We have to add z co-ordinate to txt file. We need 2-D sketch so I give 0 as z co-ordinate.
3. Create new part in Solidworks with MKS system and insert the Curve with the above .txt file using curve through XYZ points option.
4. Generate 6 different Models with different Angle of Attack by varying the Angle with respect to origin with help of Rotate Entities option.
5. Extrude the sketch with suitable thickness and save the file.
6. I use Analysis type external with time dependent (Transient), Total analysis time being 5s and output step of 1s.
7. Add working fluid as Air and in Velocity Parameters set the Velocity in X-direction to 800m/s.
8. For better understanding we have to increase the size of computational domain for 2D simulation.
9. Insert Surface Goals, Select the Outer Surface of Airfoil
1. Force (X)
2. Force (Y)
10. Insert Local Mesh by selecting the outer surface and set the refining cells. I used refining cells to 5.
11. RUN the Simulation.
12. For stop the simulation automatically after the values of drag and lift force to converged. I used goal convergence option under calculation control option.
13. Create a Cut Plot along the Cross Section to Plot Velocity Cut-Plot.
14. Create Goal Plots
1. Integrated Force along X-direction is Drag Force
2. Integrated Force along Y-direction is Lift Force.
15. Repeat the Above Procedures for all Angle of Attacks.

OUTPUT PLOTS

Case 1: For Angle of Attack=0 degree

Velocity Cut-plot

Drag Force

Lift Force

Goal Summary

Case 2: For Angle of Attack=2 degree

Velocity Cut-plot

Drag Force

Lift Force

Goal Summary

Case 3: For Angle of Attack=4 degree

Velocity Cut-plot

Drag Force

Lift Force

Goal Summary

Case 4: For Angle of Attack=6 degree

Velocity Cut-plot

Drag Force

Lift Force

Goal Summary

Case 5: For Angle of Attack=8 degree

Velocity Cut-plot

Drag Force

Lift Force

Goal Summary

Case 6: For Angle of Attack=10 degree

Velocity Cut-plot

Drag Force

Lift Force

Goal Summary

COMPARSION OF DRAG AND LIFT FORCE

CONCLUSION

• As we increase Angle of attack lift force increases linearly.
• As we increase Angle of attack drag force increases quadratic manner.
• For zero angle of attack there is no lift force.