Wind Tunnels

What is a Wind Tunnel?

English military engineer and mathematician Benjamin Robins (1707-1751) invented a whirling arm apparatus to determine drag, and with it performed some of the first experiments in aviation theory. Later on, Sir George Cayley (1773-1857) also used a whirling arm to measure drag and lift of various airfoils. However, the whirling arm did not produce reliable flow of air impacting the testing object.

Francis Herbert Wenham (1824-1904) invented the first enclosed wind tunnel in 1871. After that detailed technical data was rapidly extracted by this tool. In 1901, the Wright brothers used a simple wind tunnel to study the effects of airflow over various shapes while developing their Wright Flyer.

A wind tunnel is a research tool made to study the effects of air moving over and around objects. That means that with wind tunnels, it is possible to make a simulation of how air would react when it moves around a solid object. Wind tunnels can be used for a variety of things. They can be used to test airplane wings, cars, trains, spacecraft, and even road signs.

There are also different types of wind tunnels. A subsonic tunnel is a low speed wind tunnel with air speeds up to 400km per hour. A transonic tunnel has the same design as a subsonic tunnel, but can achieve speeds close to the speed of sound. Wind tunnels can also be categorized as open and closed tunnels.

How do Wind Tunnels Work?

Air is blown, sometimes even sucked through a tunnel containing any object that one wants to test. Typically, the air is moved through the tunnel using fans. For large wind tunnels, a single fan is not sufficient, so instead a series of multiple fans are used to provide sufficient airflow. Because of the sheer volume and air speed required, turbofans, and not electrical motors may power the fans.

The airflow created by the fans is highly turbulent because of the fan blade motion, and so is not useful for accurate measurements. For accurate measurements, the airflow has to be turbulence-free and laminar, which means that the airflow has to flow in parallel layers, with no disruption between the layers. To correct that problem, a row of closely placed vertical and horizontal air vanes are used to smooth out the turbulent airflow. That way, the air would be laminar by the time it reaches the testing object.

The inside walls of a wind tunnel are typically very smooth, since ragged edges could create turbulence. Otherwise, the accuracy of the testing would be disturbed. Even smooth walls create some drag in the airflow, so the object being tested is usually placed near the center of the tunnel.

Lighting is normally recessed into the circular walls of the tunnel and shines through windows. If the light were to be mounted on the inside surface of the tunnel, the light bulb would generate turbulence when the air blows around it. Similarly, observation is usually done through transparent portholes in the walls of the tunnel. Rather than flat windows, the observation windows may be curved to match the overall shape of the inner surface of the tunnel. That is to reduce turbulence created by the window.

Because air is transparent, it is difficult to observe the airflow itself. Instead, smoke or mist is sprayed into the tunnel ahead of the testing object. That way it is possible to see the airflow with the bare eye. Another simple way to test the airflow is to put thin strips on the testing object's surface and see how much they move.

What is the Best Airplane Wing Shape

Many different scientists around the world try to find the perfect shape of an airplane wing. The reason why airplanes are able to fly is because of their special wing shape. Wings are forced upwards because they are tilted and deflect air. A wing's trailing edge has to be sharp, and it has to be aimed diagonally downward if it is to create lift. Both the lower and upper surfaces of the wing act to deflect air. The upper surface deflects air downwards because the airflow “sticks” to the wing surface and follows the tilted wing. After the wing passes by the air remains flowing downwards. This is also known as Isaac Newton's 3rd law.

The curvature of an airplane wing determines how fast and how manoeuvrable an airplane is. In our project, we will be testing three different airplane wings. The different types of wings we will be testing are a straight, curved, and triangular wing. Instead of using smoke or mist, we will use thin strips attached to the wings' surface.