Flow over an airfoil
AIM TO SIMULATE A NACA0017AIRFOIL OVER WHICH FLUID (AIR) WILL FLOW PROVIDING DIFFERENT ANGLE OF ATTACK .
INTRODUCTION
AIRFOIL An airfoil or aerofoil 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. 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.
Airfoils are also found in propellers, fans, compressors and turbines
Examples of aerofoils in nature and within various vehicles
TERMINOLOGY
- The suction surface(a.k.a. upper surface) is generally associated with higher velocity and lower static pressure.
- The pressure surface (a.k.a. lower surface) has a comparatively higher static pressure than the suction surface. The pressure gradient between these two surfaces contributes to the lift force generated for a given airfoil
ANGLE OF ATTACT
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
PROCEDURE
1.MODELING THE AIRFOIL BY EXTACTING THE AIRFOIL DATA FROM Naca_Sample.txt file.
Caution :-check the unit in MKS
Go to sketch in fornt plane and use convert entity tool. After that we join the end of the airfoil by a line command
Click to rotate command from the move entities tool bar and give the angle of attack to 10 degree
lick on extrude boss command and give the extrude to 0.25m
2.SAVE FILE AND MOVE ON FLOW SIMULATION
- wizard (project name)
ii. creating computational domain in 2D (XY PLANE)
iii. applying global mesh as well as local mesh (which helps to refine the mesh about the surface of the airfoil so we get more accuracy
iv. create global goal and surface goal for getting the idea about the value of force, friction force ,lift force and drag force
v.creating cut plot along XY plane for getting the variation of velocity and pressure plot simulation
RUN THE SIMULATION
VIDEO LINKS :- https://youtu.be/uHK3ibjgI-U
RESULT
CASE 01
FOR ANGLE OF ATTACK = 10 DEGREE
VELOCITY CONTOUR
PRESSURE CONTOUR
DRAG AND LIFT FORCES
SG Force(X) 1 denote the DRAG Force and the SG Force(Y) 2 denote the LIFT Force
DRAG FORCE PLOT
LIFT FORCE PLOT
EXPLANATION
When we run the simulation at the angle of attack 10 degree we observe that the lift force will be almost four times of the drag force.
We observe that both force will increase suddenly and after a interval of time it will get constant.
The effect of the reaction of the fluid in velocity and pressure contour seen in a large area.
CASE 02
FOR ANGLE OF ATTACK = 8 DEGREE
VELOCITY CONTOUR
PRESSURE CONTOUR
DRAG AND LIFT FORCES
SG Force(X) 1 denote the DRAG Force and the SG Force(Y) 2 denote the LIFT Force
DRAG FORCE PLOT
LIFT FORCE PLOT
EXPLANATION
When we run the simulation at the angle of attack 08 degree we observe that the lift force will be almost four times of the drag force.
We observe that both force will increase suddenly and after a interval of time it will get constant.
The effect of the reaction of the fluid in velocity and pressure contour seen in a large area but less than the CASE 01.
CASE 03
FOR ANGLE OF ATTACK = 06 DEGREE
VELOCITY CONTOUR
PRESSURE CONTOUR
DRAG AND LIFT FORCES
SG Force(X) 1 denote the DRAG Force and the SG Force(Y) 2 denote the LIFT Force
DRAG FORCE PLOT
LIFT FORCE PLOT
EXPLANATION
When we run the simulation at the angle of attack 06 degree we observe that the lift force will be almost four times of the drag force.
We observe that both force will increase suddenly and after a interval of time it will get constant.
The effect of the reaction of the fluid in velocity and pressure contour seen in a large area but less than the CASE 01 AND CASE 02.
CASE 04
FOR ANGLE OF ATTACK = 4 DEGREE
VELOCITY CONTOUR
PRESSURE CONTOUR
DRAG AND LIFT FORCES
SG Force(X) 1 denote the DRAG Force and the SG Force(Y) 2 denote the LIFT Force
DRAG FORCE PLOT
LIFT FORCE PLOT
EXPLANATION
When we run the simulation at the angle of attack 04 degree we observe that the lift force will be almost four times of the drag force.
We observe that both force will increase suddenly and after a interval of time it will get constant.
The effect of the reaction of the fluid in velocity and pressure contour seen in a large area but less than the PREVIOUS CASES.
CASE 05
FOR ANGLE OF ATTACK = 02 DEGREE
VELOCITY CONTOUR
PRESSURE CONTOUR
DRAG AND LIFT FORCES
SG Force(X) 1 denote the DRAG Force and the SG Force(Y) 2 denote the LIFT Force
DRAG FORCE PLOT
LIFT FORCE PLOT
EXPLANATION
When we run the simulation at the angle of attack 02 degree we observe that the lift force will be almost TWO times of the drag force.
We observe that both force will increase suddenly and after a interval of time it will get constant.
The effect of the reaction of the fluid in velocity and pressure contour seen in a large area but less than the PREVIOUS CASES.
CASE 06
FOR ANGLE OF ATTACK = 00 DEGREE
VELOCITY CONTOUR
PRESSURE CONTOUR
DRAG AND LIFT FORCES
SG Force(X) 1 denote the DRAG Force and the SG Force(Y) 2 denote the LIFT Force
DRAG FORCE PLOT
LIFT FORCE PLOT
EXPLANATION
In this case we see that the averaged lift force is very less or negligible because of the angle of attack is zero due to this airfoil and the air reaction force is almost negligiable as compare to the drag force
Lift force << drag force
We can see the lift force will oscillate about the zero force line in lift force plot on other hand drag force increase suddenly then it will nearly consant .
As decrease in attack anlge the effect of velocity as well as pressure on surrounding will also decrease. We can see in the contour plot of both.
And lastly if we see carefully the value of lift force it will show negative it means the direction of lift force is opposite so this force is no longer to lift the airfoil or the machine it oppose the the lifting.
COMPARISON OF LIFT AND DRAG FORCE FOR DIFFERENT ANGLE OF ATTACK
|
Angle of attack (degree) |
Drag force (N) |
Lift force (N) |
|
10 |
1250.914 |
5009.270 |
|
8 |
955.356 |
4065.361 |
|
6 |
699.558 |
3056.078 |
|
4 |
519.701 |
2055.608 |
|
2 |
420.489 |
1031.729 |
|
0 |
400.575 |
-2.006 |
With increasing in angle of attack the drag force and lift also increase
In this case lift force increase almost linearly with increasing the angle of attack
From this graph we can say that airfoil lift after the intersection point in between 0 and 2 where the lift force overcome the drag force.
CONCLUSIONS :-
WITH THE INCREASE IN THE ANGLE OF ATTACK THE DRAG FORCE AND THE LIFT FORCE ALSO INCREASE, AS THE THR FRONTAL AREA INCREASE WITH INCREASE IN ANGLE OF ATTACK IT LEAD TO INCREASE IN DRAG FORCE AND LIFT FORCE
THE RECTION ON THE SURROUNDING WILL ASLO INCREASE WITH INCREASE THE ANGLE OF ATTACK .WE SEE IN CONTOUR