A wind tunnel is a large tube in which an object, such as an airplane model, is placed. A large fan or turbine then pushes large quantities of air past the model. Colored smoke is often added so that the scientists can see the airflow. The scientists watch the way the air flows over the model and use the data to determine how to create a more efficient design. The information gathered is both visual and read from instruments that determine wind pressure over various surfaces.
In 1897, Osbourne Reynolds, a prominent British physicist, was the first to prove that small-scale models will have the same aerodynamic properties as the same shape on a larger scale. As a result, wind tunnels need not be so large as to accommodate full-size aircraft. Carl Nyberg is credited with inventing the wind tunnel during the construction of the Flugen, an early attempt at an airplane in Sweden in 1910. The Wright brothers used a primitive wind tunnel to determine the characteristics of their airplane in North Carolina in 1913.
There are several ways to conduct measurement in a wind tunnel. One is to install small manometers, devices that measure pressure, in the chamber and on the model. The differences in pressure can then be observed at different parts of the vehicle, indicating where the air is flowing well or poorly.
Measurement can also be done using pressure-sensitive paint, which will change color according to the air pressure on it. This enables the scientists to see exactly where on the model the airflow is affected.
Modern wind tunnels employ technological advances in precise measurement, eliminating outside pressure influences. They also have very powerful fans that can create winds up to 300 miles per hour. These advances allow scientists to design airplanes that operate at very high speeds and in variable pressure situations, such as the SR-71.
A wind tunnel is a useful tool in the design of modern vehicles. As they continue to increase in measurement precision and power, they will enable scientists to create vehicles that operate efficiently at higher speeds, without dangerous and expensive testing with human pilots and drivers.