Flow over an airfoil

1. AIM

To model the flow over NACA0017 airfoil and compare the lift and drag force for the angle of attack 0,2,4,6,8,10.

2. OBJECTIVES

1. Import NACA0017 airfoil from coordinate data text file.
2. Model NACA0017
3. Analyse flow simulation of airfoil for different angle of attacks from 0 to 10 with an interval of 2.
4. Compare lifts and drag of different cases.

3. INTRODUCTION

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 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.

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 0017 airfoil is symmetrical, the 00 indicating that it has no camber. The 17 indicates that the airfoil has a 17% thickness to chord length ratio: it is 17% as thick as it is long.

Angle of attack is the angle between the line of chord of the airfoil and the relative airflow.

Image credits: http://www.aviationchief.com/angle-of-attack.html

4.CAD GEOMETRY

NACA0017 Coordinates Data text file : File

5. FLOW SIMULATION

SOLIDWORKS Flow Simulation is an intuitive Computational Fluid Dynamics (CFD) solution embedded within SOLIDWORKS 3D CAD that enables you to quickly and easily simulate liquid and gas flows through and around your designs to calculate product performance and capabilities.

The major tabs in Flow simulation

PARAMETERS

1. External flow simulation
2. Time dependent study
3. Pressure: 101325KPa
4. Temperature: 293.2K
5. Velocity along X axis: 600m/s
6. Medium : Air

STEPS

1. Input the airfoil curve from the NACA0017.txt file. (Insert>Curves>Curves trough reference point.)
2. Rotate the airfoil as per the needed angle of attack.
3. Extrude the curve after converting the curve into a sketch.
4. Activate the flow simulation plugin of solidwokrs in add-ins tab.
5. Select wizard and input respective details including medium as per parameters given above to set the project.
6. Set the computational domain to 2D and set the domain in such a way that the silumation result is not affected.
7. Edit the definition of GlobalMesh and define the mesh into more fine mesh
8. Insert a local mesh on the surface of airfoil for more accurate results.
9. Set surface goals (Forces on X and Y axis) to get drag and lift forces.
10. Run the simulation
11. Plot a cutpolt for pressure contour and velcity contour.
12. Insert goals from result to get the drag and lift force results.

Result of using local mesh = fine meshes near the surfaces

6. RESULTS, OBSERVATIONS AND CONCLUSIONS

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

Pressure and velocity contour

Drag and Lift results

Case 2: Angle of attack = 2 deg

Pressure and velocity contour

Drag and Lift results

Case 3: Angle of attack = 4 deg

Pressure and velocity contour

Drag and Lift results

Case 4: Angle of attack = 6 deg

Pressure and velocity contour

Drag and Lift results

Case 5: Angle of attack = 8 deg

Pressure and velocity contour

Drag and Lift results

Case 6: Angle of attack = 10 deg

Pressure and velocity contour

Drag and Lift results

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.

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. 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.

Conclusions

1. As the angle of attack increases the lift force on the surface also increases.
2. We can see the increase in the size of the wake region as the angle of attack increases.
3. Symmetry in velocity and pressure profile is seen in the zero degree angle of attack.
4. Lift force is nearly equal to zero in case of zero degree angle of attack compared to other cases beacuse of the symmetry of the naca0017 airfoil.
5. Providing local mesh for the airfoil surface is needed to get the optimum results.