Flow over an airfoil

OBJECTIVE:

To model flow over a NACA0017 airfoil for angle of attacks of 0, 2, 4, 6, 8 and 10 degrees and compare the lift and drag forces in each case.

SOLUTION:

Airfoil or Aerofoil is a cross sectional geometry used in aeroplane wings and turbine blades. It usually has a characteristic shape with a rounded leading edge, a sharp trailing edge and curved upper and lower surfaces. When such a shape moves through a fluid, aerodynamic force is generated on the body. This force can be resolved into two components, namely drag force (x component) and lift force (y component). This force varies with the orientation of the airfoil and the orientation can be defined using the angle of attack of the geometry. Angle of attack is the angle formed between the chord line of the airfoil and the reference line. When kept at a suitable orientation, the body deflects the incoming fluid and an aerodynamic force is generated. Generally, a positive angle of attack generates a lift force on the body.

Figure - reference [3]

The lift force and the drag force can be calculated using the following relations.

F_D = 0.5 x ρAV² x C_D

F_L = 0.5 x ρAV² x C_L

Where, C_D and C_L are the coefficient of drag and lift respectively.

The forces generated are directly proportional to C_D and C_L

The coefficient of lift increases with increase in angle of attack to a specific angle, beyond which it decreases and the drag force increases with the angle of attack. C_D and C_L are directly proportional to the forces. This relation is shown in the below figure.

figure - reference [2]

NACA airfoils are airfoil shapes developed by the National Advisory Committee for Aeronautics for aircraft wings. In this project a NACA0017 airfoil body is modelled and the lift force and drag force is analysed for a series of angle of attack (0, 2,4,6,8 and10).

Step 1:

The airfoil geometry (AG04) is generated using data from reference 1. The data can be used to create a curve in Solidworks using the curve option and the tail end points are joined using a line to create a closed profile. The profile is then extruded to a thickness of 0.25mm.

The angle of attack can be increased using the rotate entity option, and selecting the profile and point about which the rotation is to be made. One such sketch is shown in the below figure.

Step 2:

The fluid conditions are defined using the flow wizard. Air is selected as the fluid and the flow is defined as transient and external. The analysis was carried out for a time of 10 seconds with a time step of 1 second and the velocity of flow was set as 500 m/s. The analysis to be carried out was defined as 2D simulation and the computational domain was set to an appropriate size. A default global mesh was generated and a local mesh along the surface of the body was created to analyse the behaviour better.

Step 3:

The aim of the analysis is to study the lift and drag forces developed along the surface of the body, hence the goals were defined by selecting F_x and F_y along the appropriate surface. The x component gives the drag force and the y component gives the lift force.

Finally, the model is run to get the solution.

RESULTS:

Angle of Attack (deg)	Average Drag Force (N)
0	413.308
2	429.118
4	510.679
6	654.636
8	855.353
10	1165.864

Angle of Attack (deg)	Average Lift Force (N)
0	100.890
2	840.640
4	1682.182
6	2728.353
8	3646.771
10	4707.343

From the graphs, it can be inferred that both the drag force and lift force increase with an increase in angle of attack. Since C_D and C_L are directly proportional to the forces, the relation seen in the graphs is applicable for the coefficients also. This behaviour matches with that found in the literature.

References:

1. Aerofoiltools.com
2. Koay, K.K. and Tan, W.C., 2010. Computational Fluid Dynamics Study For Aerofoil. Isbn: 978–967-0120-04-1; Universiti Malaysia Pahang, pp.739-746.
3. IVAO - International Virtual Aviation Organization. https://mediawiki.ivao.aero/index.php?title=File:Airfoil.jpg