Flow over an airfoil using Solidworks
Aim- Flow over an airfoil for the angle of attacks 0,2,4,6,8,10 & compare the lift and drag forces.
Theory-
Introduction- An Airfoil is defined as the cross-section of a body that is placed in an airstream in order to generate useful aerodynamic force. An airfoil or aerofoil 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. Subsonic flight airfoils have a characteristic shape with a rounded leading edge, followed by a sharp trailing edge, often with a symmetric curvature of upper and lower surfaces. Foils of similar function designed with water as the working fluid are called hydrofoils.
Angle of attack- Angle of attack is the angle between the oncoming 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.
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 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, but cambered airfoils can generate lift at zero angle of attack. This "turning" of the air in the vicinity of the airfoil creates curved streamlines, resulting in lower pressure on one side and higher pressure on the other. This pressure difference is accompanied by a velocity difference, via Bernoulli's principle, so the resulting flowfield about the airfoil has a higher average velocity on the upper surface than on the lower surface. The lift force can be related directly to the average top/bottom velocity difference without computing the pressure by using the concept of circulation and the Kutta–Joukowski theorem.
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 varying angle 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.
Inputs and 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 1.
| Input | Value |
| Units | SI units |
| Time Dependent | Total analysis time: 5s |
| Output Time step: 1s | |
| Analysis Type | External Flow |
| Fluids | Air |
| Density | 1.225 kg/m³ |
| Inlet velocity | 600m/s |
Table 1. Inputs and boundary conditions
Procedure
1. Input the airfoil curve from the NACA0017.txt file. (Insert>Curves>Curves trough reference point) and convert entities in front plane & then using line command complete the sketch.
2. Rotate the airfoil as per the needed angle of attack (0/2/4/6/8/10).
3. Extrude the curve after converting the curve into a sketch to 0.2m.
4. The flow simulation is created using the wizard menu.
5. Select wizard and input respective details including medium as per parameters given above to set the project.
6. The analysis type is selected as external.
7. Time-dependent is selected. Total analysis time is selected as 5 sec and output time is 1sec.
8. The fluid is selected as air and velocity parameter over X-direction is selected as 600m/s and then click finish.
9. Now a computational domain is created by using the 2D option.
10. The computational domain is expanded along both y-directions and x-direction in such a way that the length after the wake region should be 5 times the length ahead of wake region.
11. The Global mesh is defined and the local mesh is defined by selecting the surface. It is refined up to a level of 3.
12. The goals option is selected then force x and force y selected after selecting the surface.
13. Run the simulation.
14. Now two cut plots are made along x-direction and pressure & velocity over the airfoil is selected.
15. Color refining is given 200.
16. A goal plot is plotted between drag force along the x-direction and lift along the y-axis.
17. The above procedure is followed for different attack angles and the following results are used to plot the necessary graphs.
Results- Results are computed and studied on different angle of attacks. Let's run one by one on the different angle of attacks.
Here,
SG Force (X)1 denotes Surface Goal force at X axis which is called as Drag Force.
SG Force (Y)1 denotes Surface Goal Force at Y axis which is called as Lift Force.
- Case 1: Angle of attack = 0 deg
A) Pressure contour
B) Velocity contour
C) Goal plot for Drag Force
D) Goal plot for Lift Force
E) Table for 0 degree Angle of Attack
| Goal Name | Unit | Value | Averaged Value | Minimum Value | Maximum Value | Progress [%] | Use In Convergence | Delta | Criteria |
| Drag Force | [N] | 302.0572355 | 302.0642017 | 302.0067197 | 302.1288315 | 100 | Yes | 0.122111819 | 5.738446647 |
| Lift Force | [N] | 1.432460771 | 1.291764283 | 0.891763903 | 1.547873723 | 100 | Yes | 0.199776935 | 0.262190195 |
- Case 2: Angle of attack = 2 deg
A) Pressure contour
B) Velocity contour
C) Goal plot for Drag Force
D) Goal plot for Lift Force
E) Table for 2 degree Angle of Attack
|
Goal Name |
Unit | Value | Averaged Value | Minimum Value | Maximum Value | Progress [%] | Use In Convergence | Delta | Criteria |
| SG Force (X) 1 | [N] | 332.896 | 332.954 | 332.752 | 333.115 | 100 | Yes | 0.363 | 6.267 |
| SG Force (Y) 1 | [N] | 833.795 | 833.278 | 832.234 | 834.166 | 100 | Yes | 1.931 | 6.646 |
- Case 3: Angle of attack = 4 deg
A) Pressure contour
B) Velocity contour
C) Goal plot for Drag Force
D) Goal plot for Lift Force
E) Table for 4 degree Angle of Attack
| Goal Name | Unit | Value | Averaged Value | Minimum Value | Maximum Value | Progress [%] | Use In Convergence | Delta | Criteria |
| SG Force (X) 1 | [N] | 413.441 | 413.531 | 413.381 | 413.691 | 100 | Yes | 0.31 | 7.634 |
| SG Force (Y) 1 | [N] | 1640.576 | 1635.409 | 1628.029 | 1640.576 | 100 | Yes | 12.546 | 16.4 |
- Case 4: Angle of attack = 6 deg
A) Pressure contour
B) Velocity contour
C) Goal plot for Drag Force
D) Goal plot for Lift Force
E) Table for 6 degree Angle of Attack
| Goal Name | Unit | Value | Averaged Value | Minimum Value | Maximum Value | Progress [%] | Use In Convergence | Delta | Criteria |
| SG Force (X) 1 | [N] | 552.675 | 552.887 | 552.623 | 553.316 | 100 | Yes | 0.693 | 10.112 |
| SG Force (Y) 1 | [N] | 2442.035 | 2440.176 | 2433.25 | 2443.902 | 100 | Yes | 10.652 | 28.724 |
- Case 5: Angle of attack = 8 deg
A) Pressure contour
B) Velocity contour
C) Goal plot for Drag Force
D) Goal plot for Lift Force
E) Table for 8 degree Angle of Attack
| Goal Name | Unit | Value | Averaged Value | Minimum Value | Maximum Value | Progress [%] | Use In Convergence | Delta | Criteria |
| SG Force (X) 1 | [N] | 756.362 | 756.334 | 755.575 | 757.383 | 100 | Yes | 0.331 | 13.882 |
| SG Force (Y) 1 | [N] | 3250.725 | 3249.883 | 3246.644 | 3252.17 | 100 | Yes | 0.81 | 43.879 |
- Case 6: Angle of attack = 10 deg
A) Pressure contour
B) Velocity contour
C) Goal plot for Drag Force
D) Goal plot for Lift Force
E) Table for 10 degree Angle of Attack
| Goal Name | Unit | Value | Averaged Value | Minimum Value | Maximum Value | Progress [%] | Use In Convergence | Delta | Criteria |
| SG Force (X) 1 | [N] | 996.038 | 995.723 | 994.203 | 996.709 | 100 | Yes | 0.148 | 18.327 |
| SG Force (Y) 1 | [N] | 4034.082 | 4033.199 | 4027.911 | 4037.246 | 100 | Yes | 0.746 | 60.955 |
Comparisons
- Averaged Drag Force vs Angle of Attack
-
Averaged Lift Force vs Angle of Attack
Conclusions
1. With the increase in angle of attack, Drag force increases slowly and lift force increases rapidly. With the increase in angle of attack, the velocity of air over the airfoil increased.
2. We can see that the pressure region below the airfoil turns to light blue as the angle of attack increases. This indicates increase in pressure below aerofoil as angle of attack increases.The pressure region above the airfoil turns to dark blue as the angle of attack increases. This indicates decrease in pressure above aerofoil as angle of attack increases. So ineffect the pressure difference between above and below airfoil is increasing as angle of attch increases.This is the reason for the increase in lift force.
3. The increase in lift force with increase in angle of attack is almost linear while that of drag is nonlinear. Similary same effect can also be seen in velocity contour. When more air flows through the upper region of airfoil compared to lower region, velocity will be more in this upper region and pressure will drop in this area. This will create a suction which causes the lift force.
4. We can see the increase in the size of the wake region as the angle of attack increases.
5. Symmetry in velocity and pressure profile is seen in the zero degree angle of attack.
6. Lift force is nearly equal to zero in case of zero degree angle of attack compared to other cases because of the symmetry of the Naca0017 airfoil.
Note- The name of the part signies the angle of attack in that part. For example- 0 AOA means Airfoil with 0 degree angle of attack.