Flow over an airfoil

Aim: To simulate flow over Naca Airfoil

objective:

• To simulate flow over Naca airfoil
• To perform parametric study for different angle of attack
• Do the analysis of result

Therotical background:

An aerofoil is the term used to describe the cross-sectional shape of an object that, when moved through a fluid such as air, creates an aerodynamic force. Aerofoils are employed on aircraft as wings to produce lift or as propeller blades to produce thrust. Both these forces are produce perpendicular to the air flow. Drag is a consequence of the production of lift/thrust and acts parallel to the airflow.

Other aerofoil surfaces includes tailplanes, fins, winglets, and helicopter rotor blades. Control surfaces (e.g. ailerons, elevators and rudders) are shaped to contribute to the overall aerofoil section of the wing or empennage .

Airfoil terminology:

Several terms are used to describe aerofoils

• 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

By altering each of the above features of an aerofoil, the designer is able to adjust the performance of the wing so that it is suitable for it's particular task. For example, a crop duster may have a thick, high camber wing that produces a large amount of lift at low speed. Alternatively, a jet would have a thin wing with minimal camber to allow it to cruise at high speeds.

How it works:

The basic principle behind an aerofoil is described by bernoullis 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 aerofoil 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 aerofoil will stall.

Geometry:

Input data:

flow type:external

x-velocity : 600 m/s

fluid: Air

Procedure:

• Use Naca airfoil data point file to create curve .
• Provide input data to simulation and velocity as 600 m/s.
• Refine the mesh near the surface of airfoil.
• run the solution it will take time to converge the solution
• perform parametric study by changing angle of attack.

Error Encountered:

• Make the computational domain large enough so that there will not be any reflection in pressure and velocity variation.

plot:

• Angle of attack =10 degree

• Angle of attack = 8 degree

• Angle of attack = 6 degree

• angle of attack = 4 degree

• angle of attack = 2 degree

• Angle of attack = 0 degree

Surface goal :

• 10 degree angle of attack

• 8 degree angle of attack

• 6 degree angle of attack

• 4 degree angle of attack

• 2 degree angle of attack

• 0 degree angle of attack

Conclusion:

• as angle of attack increases lift and drag force also increases .
• variation of drag force is as follow
• Variation of lift force is as follows:

Result:

• CFD analysis of Naca airfoil has been done successfully