Flow simulation of NACA airfoil at different angle of attacks

AIM: Determine the drag force and lift force for NACA0017 airfoil at different angle of attack.

OBJECTIVES:

• Model the flow over a NACA0017 airfoil.
• For the angle of attacks 0,2,4,6,8,10 compare the lift and drag forces.

THOERY:

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).

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.

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.

In fluid dynamics, angle of attack (AOA or α{\displaystyle \alpha }) 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. Angle of attack is the angle between the body's reference line and the oncoming flow. This article focuses on the most common application, the angle of attack of a wing or airfoil moving through air.

Lift is the force that directly opposes the weight of an airplane and holds the airplane in the air. Lift is generated by every part of the airplane, but most of the lift on a normal airliner is generated by the wings. Lift is a mechanical aerodynamic force produced by the motion of the airplane through the air. Because lift is a force, it is a vector quantity, having both a magnitude and a direction associated with it. Lift acts through the center of pressure of the object and is directed perpendicular to the flow direction. There are several factors which affect the magnitude of lift.

Drag is the aerodynamic force that opposes an aircraft's motion through the air. Drag is generated by every part of the airplane (even the engines!). Drag is a mechanical force. It is generated by the interaction and contact of a solid body with a fluid (liquid or gas). It is not generated by a force field, in the sense of a gravitational field or an electromagnetic field, where one object can affect another object without being in physical contact.

PROCEDURE:

Modelling –

Click on new part->insert->curve->browse->file->OK. [Note: Select MKS before inserting curve]

Select front plane->curve->convert entity->line, join the opening ends of the curve->OK.

To give angle of attack, in sketcher select rotate enitity->spline and line->origin point->give angle value->OK.

Select the curve sketch->boss->midplane->1m.

Flow simulation –

Select SOLIDWORKS Flow Simulation->New Wizard and select following option

Analysis type = external

Total Analysis time = 5sec

Output time step = 1sec

Fluid = Air

Flow type = Laminar and turbulent

Wall condition = Adiabatic wall

Pressure = 101325 P

Temperature = 293.2 K

Velocity in X direction = 600m/s

Now, Right-click on Computational Domain->2D Simulation->XY Plane and select domain such that the length & height of the domain at inflow should be 5 times the chord length and distance at outflow should be 10-15 times the chord length.

Right-click on goals and provide following goals

Global goal = Force(x), Force(y), Friction Force(x), Friction Force(y)

Surface goal = Force(x) referred as drag force & Force(y) referred as lift force

RESULTS:

For angel of attack 0 degree

Velocity Contour

Velocity Contour closeup

Pressure Contour

Pressure Contour closeup

Drag force and Lift Force

For angel of attack 2 degree

Velocity Contour

Velocity Contour closeup

Pressure Contour

Pressure Contour closeup

Drag Force and Lift Force

For angel of attack 4 degree

Velocity Contour

Velocity Contour closeup

Pressure Contour

Pressure Contour closeup

Drag Force and Lift Force

For angel of attack 6 degree

Velocity Contour

Velocity Contour closeup

Pressure Contour

Pressure Contour closeup

Drag Force and Lift Force

For angel of attack 8 degree

Velocity Contour

Velocity Contour closeup

Pressure Contour

Pressure Contour closeup

Drag Force and Lift Force

For angel of attack 10 degree

Velocity Contour

Velocity Contour closeup

Pressure Contour

Pressure Contour closeup

Drag Force and Lift Force

Pressure Contour for angel of attack 0,2,4,6,8 and 10 respectively compared side by side

CONCLUSION:

1. On increasing the angle of attack (AOA) from 0⁰ to 10⁰, the drag & lift force increases.
2. Since, up to 10⁰ of AOA, the lift force is increasing. Therefore, the stall angle has not achieved yet.
3. In first case, the lift forces are negative as the camber profile is curved above the horizontal axis of the airfoil.
4. As the AOA increases up to 8⁰, the maximum velocity of air over the airfoil increases with increase in AOA but at 10⁰ AOA, it reduces due to sudden high increase in the drag force.
5. The maximum pressure experienced by the airfoil is at 0⁰ AOA and the pressure exerted over the airfoil reduces as the AOA increases.
6. Comparing all the velocity contour we can observe that at 0⁰ AOA, the velocity distribution of air over the upper & lower surface of the airfoil is almost symmetrical but as the AOA increases, the velocity of the air over the upper surface increases and the velocity of air decreases over the lower surface of the airfoil.
7. Comparing all pressure contour, we can observe that at 0⁰ AOA, the pressure distribution over the upper & lower surface of the airfoil is almost symmetrical but as the AOA increases, a lower pressure region is formed on the upper surface while a higher-pressure region is formed on the lower surface. This pressure difference created on the upper & lower surface of the airfoil causes the airfoil to generate lift.

REFERENCES:

http://airfoiltools.com/search/airfoils

LINKS: GDive