Flow over an airfoil

Aim: 

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

Introduction:

Computational fluid dynamics (CFD) is a branch of fluid mechanics that uses numerical analysis and data structures to analyze and solve problems that involve fluid flows. Computers are used to perform the calculations required to simulate the free-stream flow of the fluid, and the interaction of the fluid (liquids and gases) with surfaces defined by boundary conditions.

Here Solidworks flow simulation is used for simulation.

Theory:

The lift force of the airfoil depends on the angle of attack (AOA). Generally, Airfoil requires a positive angle of attack for lift (But a cambered airfoil can generate lift at zero angles of attack as well). Particularly subsonic airfoils are more round leading edge making the airfoil very insensitive to the angle of attack. Supersonic airfoils on the other hand have a sharper leading edge which is very sensitive to the angle of attack. So, in modern-day aviation, airfoils are selected on various parameters each of them optimized for their area of application. 

Drag is the force experienced by an object representing the resistance to its movement through a fluid. Sometimes called wind resistance or fluid resistance, it acts in the opposite direction to the relative motion between the object and the fluid.

Drag coefficient: Resistive force against the body caused by the body moving through the fluid. It is in the opposite direction to the velocity of the flow. The relative velocity between body and flow is called the drag coefficient. 

`Cd=(2Fd)/(ρ*A*v^2)` , where Fd = Drag force

ρ = mass density of fluid,

v = flow speed of the object relative to the fluid.

A = Reference Area

Lift is the component of this force that is perpendicular to the oncoming flow direction.[1] It contrasts with the drag force, which is the component of the force parallel to the flow direction.

Lift Coefficient: Lift Coefficient is a dimensionless coefficient that relates the lift generated by a lifting body to the fluid density around the body, the fluid velocity, and an associated reference area A lifting body is a foil.

`Cl=(2Fl)/(ρ*A*v^2)` , where FL = Lifting force

ρ = mass density of fluid,

v = flow speed of the object relative to the fluid.

A = Reference Area

Simulation Setup:

• Air foil design is of Naca0017.
• Attack angles be 0, 2, 4, 6, 8, 10.
• Type of flow is external.
• Simulation is time dependent having flow time 5sec and the output will be obtained for every 1sec.
• Fluid is air.
• Flow velocity is in positive x axis at 600 m/s.
• length of the chord is 1m
• Surface force along x direction is drag force.
• Surface force along y direction is lift force.

Note: I joined the curve with 2 tangent lines to get an appropriate shape.

Results:

Case 1: Angle of attack is 0 deg

Case 2: Angle of attack is 2 deg

Case 3: Angle of attack is 4 deg

Case 4: Angle of attack is 6 deg

Case 5: Angle of attack is 8 deg

Case 6: Angle of attack is 10 deg

Comparison:

From comparing the lift and drag forces from each case. We can conclude that these values increase as the angle of attack increases (From 0deg to 10deg)

Conclusion:

• From the plots it is clear that Lift force increases with angle of attack.
• From the plots it is clear that drag force increases with angle of attack.
• At 0 degree the lift force is not seems to significant to consider.