Transient flow over a GOE 481A AIRFOIL using Solidworks Flow Simulation

AIM: To determine the various values of drag forces on GOE 481A AIRFOIL and lift forces at different vales of angle of attack.

OBJECTIVE:

1. Model the flow over a NACA0017 airfoil

2. For the angle of attacks 0,2,4,6,8,10 compare the lift and drag forces

3. Export the global goals into excel and plot a graph of the lift forces and drag forces versus velocity.

THEORY:

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

Several terms are used to describe airfoils

• Leading Edge = Forward edge of the aerofoil
• Trailing Edge = Aft edge of the aerofoil
• Chord = Line connecting the leading and trailing edge. Denotes the length of the aerofoil
• Mean Camber Line = Line drawn half way between the upper and lower surface of the aerofoil. Denotes the amount of curvature of the wing
• Point of Maximum Thickness = Thickest part of the wing expressed as a percentage of the chord.

The basic principle behind an airfoil is described by Bernoulli's theorem. Basically this states that total pressure is equal to static pressure (due to the weight of air above) plus dynamic pressure (due to the motion of air).

Air that travels over the top surface of the airfoil has to travel faster and thus gains dynamic pressure. The subsequent loss of static pressure creates a pressure difference between the upper and lower surfaces that is called lift and opposes the weight of an aircraft (or thrust that opposes drag).

As the angle of attack (the angle between the chord line and relative air flow) is increased, more lift is created. Once the critical angle of attack is reached (generally around 14 degrees) the airfoil will stall.

The basic equation of the lift of the airfoil is given by:

FLOW SIMULATION SETUP:

1. A CAD model of an airfoil is created in Solidworks, by drawing a curve inserting the co-ordinates of the various points of the curve and joining those point together, and then extruding the airfoil.

2. Enable Flow Simulation from the add-ins menu.

3. After that, the flow simulation wizard is used to set up all the parameters of the mathematical model.

4. Steps for wizard: (Note that gravity is checked, i.e. there is gravity involved in this study)

1. Give a suitable project name.
2. Select a proper unit system, preferably SI system.
3. Select a flow type. In our case, the flow is over the cylinder. Hence, it is an external flow.
4. Select the proper fluid that is used in the simulation. In this case, the fluid is air. Also, select the proper flow type, depending on the nature of the flow i.e laminar, turbulent or mixed.
5. Set wall conditions as it is. Do not make any changes as far as the challenge is considered.
6. Now, set the velocity of the flow of the fluid along the proper direction, in X direction in our case.

5. Since this is an external flow, we will not be specifying any boundary conditions.

6. Here, since velocity is not given, we can assume it to be 650`m/s` in the X-direction, since an airfoil is always subjected to high velocity.

7. Now, the computational domain is needed to be set in 2D. Also, the size of the domain should be significantly higher, to prevent reflection of the contour.

8. Now, check the mesh size. If it is adequate, the leave the global mesh as it is. However, it is necessary to refine the mesh locally, near the surface of the airfoil. Hence, reduce the size of the mesh to improve the accuracy of the results.

9. Set the global goals, i.e the values that must be calculated after the simulation study. In our case, the main goal is to find out the lift forces and the drag forces. Same must be set for the surface goals.

10. The same procedure ust be repeated for various values of angle of attack.

OBSERVATION AND RESULTS:

For Angle of Attack = `0^0`

Lift force:

Drag force:

For Angle of Attack = `2^0`

Lift force:

Drag force:

For Angle of Attack = `4^0`

Lift force:

Drag force:

For Angle of Attack = `6^0`

Lift force:

Drag force:

For Angle of Attack = `8^0`

Lift force:

Drag force:

For Angle of Attack = `10^0`

Lift force:

Drag force:

CONCLUSION:

From the plots, we see that the value of lift force is a direct function of the angle of attack. As the angle of attack increases, the values of lift force also increases. Also, the magnitude of the lift force is dependent on the nature of the profile of the airfoil.

On the other hand, the value of drag force is higher at `0^0` , so it is not an optimal angle. This increase in drag force ends at a certain angle of attack, and the lift force also starts decreasing. This point is called the stalling point nd the corresponding angle is referred to as the critical angle of attack.