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Saturday, April 5, 2014

Airfoil Flow Visualization

I recently had to the opportunity to do something a little different from what you might be used to seeing around here. As an aeronautical engineer by education, it is finally time to share some of that and take a break from the more traditional side of craftsmanship (but not for long!)

Although the pictures had to be modified heavily to capture the contrast of the flow, here are a series of visualizations of a NACA 0012 airfoil cross section using helium bubbles in the airstream. A quick background on what this means and why it is important. This particular airfoil (read, wing) is symmetric, meaning if you were to draw a straight line from the leading edge to the trailing edge, the two halves would be the same.

As you vary the angle of attack, α, a number of things happen. Without going too deep into what is happening aerodynamically, generated lift changes and the amount of air that adheres to the surfaces of the wing changes. At lower angles of attack, more air will 'stick' to the wing. The higher it goes, a turbulent section begins to form until virtually the entire wing fails to keep the flow attached, and thus generate significantly less lift.

For the photos below, the airfoil varies from 0 to 24 degrees (max on the armature), and in the end of the video changes from 24 to -8 degrees where you can see what happens and when the flow reattaches.

Unfortunately, several of the images needed to be taken at a slight angle to eliminate the glare from the wind tunnel window. In the video, the same angles of attack are used as in the photos.

α = 0 degrees

α = 4 degrees

α = 12 degrees

α = 20 degrees

α = 24 degrees

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