Flow over an airfoil

Flow over a NACA0017 airfoil using SolidWorks

1. AIM : To model the flow over a NACA0017 airfoil in SolidWorks.

2. OBJECTIVE :

• To perform an external flow simulation on NACA0017 airfoil.
• To do flow simulation for the angle of attacks 0, 2, 4, 6, 8, and 10 degrees.
• To compare the lift and drag forces for all the above angle of attacks separately.

3. INTRODUCTION :

3.1 NACA airfoil : - The NACA airfoils are airfoil shapes for aircraft wings developed by the National Advisory Committee for Aeronautics (NACA). The shape of the NACA airfoils is described using a series of digits following the word “NACA”. The parameters in the numerical code can be entered into equations to precisely generate the cross-section of the airfoil and calculate its properties.

Fig.1: Airplane Sketch-scaled

Four-digit series :

The NACA four-digit wing sections define the profile by -

1. First digit describing maximum camber as percentage of the chord.
2. Second digit describing the distance of maximum camber from the airfoil leading edge in tenths of the chord.
3. Last two digits describing maximum thickness of the airfoil as percent of the chord.

Fig.2: Wing profile nomenclature

3.2 Angle of Attack : - The Angle of Attack is the angle at which relative wind meets an Airfoil. It is the angle formed by the Chord of the airfoil and the direction of the relative wind or the vector representing the relative motion between the aircraft and the atmosphere.

A symmetrical airfoil will generate zero lift at zero angle of attack. But as the angle of attack increases, the air is deflected through a larger angle and the vertical component of the air stream velocity increases, resulting in more lift. For small angles, a symmetrical airfoil will generate a lift force roughly proportional to the angle of attack.

Fig.3: Forces on an aircraft wing

3.3 Lift force : - The lift force, lifting force or simply lift is the sum of all the forces on a body that force it to move perpendicular to the direction of flow.

The most common type of lift is that of a wing of an aircraft. But there are many other common uses such as propellers on both aircraft and boats, rotors on helicopters, fan blades, sails on sailboats, and wind turbines.

While the common meaning of the term "lift" suggests an "upwards" action, lift can be in any direction. For instance, for a sail the lift is horizontal, and for the wing on a race car the lift is down.

There are a number of ways of explaining the production of lift; some are more complicated than others, some have been shown to be false. The simplest explanation is that the wing deflects air downward, and the reaction pushes the wing up.

3.4 Drag force : - A drag force is the resistance force caused by the motion of a body through a fluid, such as water or air. A drag force acts opposite to the direction of the oncoming flow velocity. This is the relative velocity between the body and the fluid.

4. BODY OF CONTENT :

For performing external flow simulation for NACA017 airfoil, we will need the 3D model of airfoil.

So, first we need to design 3D model of airfoil. And for designing any 3D model, we have to design 2D sketch of the model first, after that we can proceed for designing 3D model.

For designing we need to insert the x, y and z co-ordinates for various points of airfoil under the curve section in SolidWorks. After doing so, we will get shape for our airfoil and we will make it as a closed sketch by adding a line at the opening side of airfoil. And after all these, we will get sketch of airfoil as,

fig. 2D sketch of NACA0017 airfoil

• All dimensions are in the unit system of MKS (i.e. meter, kilogram, seconds).
• Front plane is used here for 2D sketch of airfoil.

Lin for the text file –

https://drive.google.com/file/d/12ZIqEQ5SuVYwODgf_EIo3Q8A_N1a8mcP/view?usp=sharing

Now, going to extrude the airfoil sketch to form a solid airfoil in 3-Dimensional structure.

Dimensions taken for the Airfoil –

1. Extruded by = 0.2 m

3D Model –

Fig. 3D model of NACA0017 airfoil

Now, we will go to the flow simulation in SolidWorks.

Parameters taken: -

• Tyoe of Flow Simulation = External flow
• Medium = Air
• Pressure = 101325 Pa
• Temperature = 293.2 K
• Velocity along x-axis = 600 m/s
• Study type = Time-dependent study

As we have to perform an external flow simulation so, we need to consider a gas/fluid which will flow over the airfoil for our flow simulation study.

Here, we are going to consider air as a gas for our external flow simulation study.

We are also going to do Time-dependent simulation here. And assigning time-dependent as follows –

• Total analysis time = 5 sec
• Output time step = 1 sec

After that, for a flow simulation there must be some velocity for the fluid or, gas. So, here going to assign the inlet velocity of air = 600 m/s along X-axis.

Further steps for Flow Simulation: –

Activate the flow simulation and add the parameters in the wizard command.

Sketch 2D computational domain and assign a domain size,

Fig. Setting up 2D computational domain

Now, edit the global mesh into fine mesh and local mesh at the face of the curve for refinement.

Set surface goals to get the drag and lift force.

Run the simulation.

Insert plots of velocity and pressure.

Insert goals from results to get drag and lift force as results.

5. RESULTS :

Here,

Integrated force along the x-axis is Drag force

Integrated force along the y-axis is Lift force.

Also,

SG(X) represents the surface goal at x-axis i.e. Drag force

SG(Y) represents the surface goal at y-axis i.e. Lift force.

5.1Study-1: Angle of attack = 0°

a. Velocity distribution –

b. Pressure distribution –

• Drag force and Lift force at 0° angle of attack –

5.2 Study-2: Angle of attack = 2°

a. Velocity distribution –

b. Pressure distribution –

• Drag force and Lift force at 2° angle of attack –

5.3 Study-3: Angle of attack = 4°

a. Velocity distribution –

b. Pressure distribution –

• Drag force and Lift force at 4° angle of attack –

5.4 Study-4: Angle of attack = 6°

a. Velocity distribution –

b. Pressure distribution –

• Drag force and Lift force at 6° angle of attack –

5.5 Study-5: Angle of attack = 8°

a. Velocity distribution –

b. Pressure distribution –

5.6 Study-6: Angle of attack = 10°

a. Velocity distribution –

b. Pressure distribution –

6. OBSERVATIONS & CONCLUSIONS :

1. Lift at 0° angle of attack is approximately zero for symmetrical airfoils.
2. Also there is symmetry found in velocity and pressure plot at 0° angle of attack.
3. Lift force increases with increase in angle of attack upto critical angle of attack after which it tends to decrease.
4. Increasing the angle of attack results in increase in drag force and coefficient of drag due to increase in frontal area.
5. At critical angle of attack, flow separation occurs and it will lead to stalling.