Flow over an airfoil

Aim:

CFD analysis of subsonic flow over an NACA0017 airfoil over various angle of attacks and compare the lift and drag force.

Theory:

Airfoil:

An airfoil (American English) or aerofoil (British English) is the cross-sectional shape of a wing, blade (of a propeller, rotor, or turbine), or sail (as seen in cross-section).

Angle of attack:

Angle of attack is the angle between a reference line on a body (often the chord line of an airfoil) and the vector representing the relative motion between the body and the fluid through which it is moving.

Effects of angle of attack:

With the increase in angle of attack, lift force also increases proportionately up to a critical point called as critical angle of attack. At the critical angle of attack upper flow is more separated and the airfoil produces maximum coefficient of lift.

The study of airfoil behaviour to varying angle of attacks is made in order to determine the best possible dimension for practical condition. In most aeroplanes this is about 16 to 18 degrees. During a cruise, the requirement is to maintain the angle of attack such that drag experienced is minimum so as to use minimum thrust and to improve fuel consumption, this could occur at an angle of 3 to 5 degrees.

Procedure:

• The coordinates file was downloaded for NACA0017 airfoil.
• Then the curve was obtained using curve through xyz geometry.
• Then, convert entities option was used to get the sketch in front plane.
• Close the sketch at the end by joining a line.
• Then the sketch was extruded up to 0.20m.
• Then wizard option was set up in flow simulation option of SOLIDWORKS to set up the necessary condition.
• The necessary conditions were setting the flow simulation to external, taking the time for analysis as 5 sec with a step count of 1 sec, taking the fluid as air for simulation against airfoil,, taking the velocity in x direction to be 600m/s.
• The computational domain length was changed according to the chord length of the airfoil.
• The inflow area was taken as 5m and the outflow area was taken as 15m and the total height of computational domain was taken as 10m.
• The appropriate goals were defined such as global goals: Force (x direction), Force (y direction), frictional force in x and y direction. Surface goals: lift force and drag force.
• Local mesh was inserted at the top of airfoil for better results.
• This process was repeated for different angle of attacks and the simulation was run.

Outputs:

Angle of attack at 0 degree:

Velocity cut plot:

Lift and drag force:

Angle of attack at 2 degrees:

Velocity cut plot:

Lift and drag force:

Angle of attack at 4 degrees:

Velocity cut plot:

Lift and drag force:

Angle of attack at 6 degrees:

Velocity cut plot:

Lift and drag force:

Angle of attack at 8 degrees:

Velocity cut plot:

Lift and drag force:

Angle of attack at 10 degrees:

Velocity cut plot:

Lift and drag force:

Comparison study:

Lift and drag force for different angle of attack:

Angle of attack	Drag force	Lift force
0 degree	300.741 N	0.121 N
2 degrees	305.620 N	836.217 N
4 degrees	414.105 N	1646.681 N
6 degrees	554.254 N	2445.207 N
8 degrees	755.506 N	3243.596 N
10 degrees	997.677 N	4048.836 N

Comparing drag force against angle of attack:

Comparing lift force against angle of attack:

Comparing drag force against lift force:

Conclusion:

Sucessful analysis of NACA0017 airfoil has been made at various angle of attacks has been made and the following observations have been made:

• With increase in angle of attack drag force increases slowly and lift force increases rapidly.
• With increase in angle of attack, the velocity of air over airfoil increased.