Flow over an airfoil
NACA Airfoil test at different Angle of Attacks.
Aim: To analyze the drag and lift force of airfoil at different angle of attack.
Objective:
- Create an airfoil using NACA airfoil data and perform flow simulation on it.
- Calculate the drag at and lift forces at different angle of attacks.
- Examine the difference between the respective forces of different angle of attack.
- Compare the forces.
Theory
Airfoil:
An airfoil is the cross-sectional shape of a wing, blade (of a propeller, rotor, or turbine).
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 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.
Flow of steps followed while making the project:
The airfoil used in the project is NACA0017 airfoil. The curve data of the airfoil is taken from the link. After taking the data, it is formatted in such a way that Solidworks can read it. In order to do it, coordinates along Z axis are specified as zero. Solidworks needs coefficients of all three axis to extract the data in the form of curve.
After formatting, a curve is made using this data. To extrude it, first the curve entity is converted into sketch and then extruded by 0.1 m.
Next step is to create a flow simulation
The flow simulation is created by setting up the ‘Wizard’. After opening the wizard, first thing to do is specifying the name of the project i.e. Airfoil at AOA 0 and click next.
The values present in the next window should be kept constant and click next. In the next window, flow should be determined as external or internal. Here, external flow type is selected and time-dependent option is selected in which total analysis time is kept as 5 sec and output time stamp is kept at 1 sec. By doing this the fluid will take 5 sec to travel from inlet to outlet and in that time period, the output is taken at the interval of 1 sec.
In next window, flowing fluid is selected as air and click next. Next window is kept at default and after clicking next, velocity is specified as 600 m/s along X direction and clicked finished.
After setting up the flow simulation, the properties of computational domain is changed by selecting the type of simulation as 2D simulation along XY plane and dragging the domain length. The dimensions of the domain can be specified by entering the distance along the axes or by dragging the arrows of domain to enlarge it.
Now, goals are provided by firstly selecting the global goals as force along X axis and Y axis, and friction force along X axis and Y axis. Secondly, surface goals are added by selecting the force along X axis and Y axis. To select surface goals, face of airfoil is selected. The surface goal along X axis is drag force and along Y axis is lift force.
To refine the calculation near the face of the airfoil, local mesh is added along the surface of airfoil.
After that ‘Run’ button is clicked to perform the calculations.
A new solver window will popup which solves the iterations for the flow simulations. Due to the velocity provided, the flow becomes supersonic and thus the solver needs to be stopped manually. In this window, the graph for drag and lift forces are tracked and when the graph becomes a straight line i.e. there is no variations in the values of graph, the solver is stopped and closed.
Then the results are examined by observing the cut plots for velocity and pressure and also by studying the goal plots of lift and drag forces.
The drag and lift forces are calculated by setting the AOA as 0°,2°,4°,6°,8° and 10° respectively.
Results obtained are shown below
Airfoil at Angle of Attack of 0°:
Velocity cut plot
Pressure cut plot
Lift force
Drag force
Airfoil at Angle of Attack of 2°:
Velocity cut plot
Pressure cut plot
Lift force
Drag force
Airfoil at Angle of Attack of 4°:
Velocity cut plot
Pressure cut plot
Lift force
Drag force
Airfoil at Angle of Attack of 6°:
Velocity cut plot
Pressure cut plot
Lift force
Drag force
Airfoil at Angle of Attack of 8°:
Velocity cut plot
Pressure cut plot
Lift force
Drag force
Airfoil at Angle of Attack of 10°:
Velocity cut plot
Pressure cut plot
Lift force
Drag force
RESULT
In an airfoil, an increase in angle of attack leads to an increase in the coefficient of lift up until the point it doesn't. The airfoil is symmetrical, due to which it produces less total lift but when it drops off, it drops off slowly. An increase in angle of attack results in an increase in both lift and induced drag, up to a certain point. After that point the lift and drag becomes constant further.
In the pressure cut plot, it is observed that the pressure in the space behind the airfoil while AOA is more than 0° is least.
Reference: