Flow over an airfoil
1. INTRODUCTION
Airfoil is defined as the cross-section of a body that is placed in an airstream in order to generate useful aerodynamic force.
Computational Fluid Dynamics (CFD) (CFD) is a branch of fluid mechanics that uses numerical methods and algorithms to solve complex problems involving fluid flow.
The angle of attack is the angle between the incoming air or relative wind and a reference line on the airplane or wing. Sometimes, the reference line is a line connecting the leading edge and trailing edge at some average point on the wing.
Effect of angle of attack:
Increases as the angle of attack increase the lift force increase proportionately. And a certain point, called critical angle of attack, upper surface flow is more separated and the airfoil or wing is producing its maximum coefficient of lift. The study of airfoil behavior to the varying angles of attacks is made in order to determine the best possible dimensions for practical conditions. In most airplanes, this is about 16 to 18 degrees. During a cruise, the requirement is to maintain the angle of attack where the total drag on the airplane is minimum so as to use the minimum thrust and therefore, minimum fuel consumption. This could occur at an angle of about 3 to 5 degrees.
NACA-0017 data taken from below link
https://drive.google.com/open?id=12ZIqEQ5SuVYwODgf_EIo3Q8A_N1a8mcP
The present study aims to analyze the flow field for NACA-0017 airfoil at various angles of attack and also to compare the lift and drag force.
2. 2D GEOMETRY AND 3D MODEL
The curve point is inserted in the Solidworks sketch through the XYZ data points curve option. Then the sketch is formed. Initially, it is kept in the same orientation and it is rotated to various angles using rotate entities option.
After inserting the sketch it is extruded to a distance of 0.4m.
3. BOUNDARY CONDITIONS
The problem consists of flow around an airfoil at various angles of attack (0, 2, 4, 6, 8, 10 degrees). The inputs and boundary conditions are presented in Table
|
INPUTS |
VALUE |
|
Unit |
SI Unit |
|
Analysis type |
External flow |
|
Fluid |
Air |
|
Time-dependent |
Total Analysis Time: 5s |
|
Output Step Time: 1s |
|
|
Density |
1.225 kg/m3 |
|
Inlet velocity |
600 m/s |
|
Chord length |
1 m |
4. PROCEDURE
Once the part file is saved flow simulation is activated and the above boundary conditions are given as output. The computational domain is increased 15 times that of the geometry and the simulation is run.
5. RESULT
Results are computed and studied on a different angle of attacks.
Here,
The integrated force along the x-axis is Drag force.
Integrated force along the y-axis is Lift force.
CASE 1: 0 DEG ANGLE OF ATTACK
CASE 2: 2 DEG ANGLE OF ATTACK
CASE 3: 4 DEG ANGLE OF ATTACK
CASE 4: 6 DEG ANGLE OF ATTACK
CASE 5: 8 DEG ANGLE OF ATTACK
CASE 6: 10 DEG ANGLE OF ATTACK
COMPARISON
| Degree | Average Drag force (N) | Average Lift force (N) |
| 0 | 602.271 | 0.458 |
| 2 | 664.932 | 1670.548 |
| 4 | 824.364 | 3287.902 |
| 6 | 1103.723 | 4887.495 |
| 8 | 1511.176 | 6498.131 |
| 10 | 1992.278 | 8075.362 |
6. CONCLUSION
From the above graphs, the average drag force and lift force is studied at the various angle of attack. It is also found that the average drag force varies in a quadratic manner and the average lift force varies in a linear manner. It is also observed that the constant value drag or lift force is achieved in the earlier iterations as the angle of attack increases. The drag force is nearly constant at a small angle of ± 5 deg, but as the angle of attack increases the drag force drastically changes due to the increase in the frontal area and boundary layer thickness.