Early aerodynamic testing
Before the advent of the wind tunnel, experimenters would use a whirling arm to measure drag and lift on models. The weakness of this approach was that the model would be travelling in its own wake.
In 1901, the Wright brothers tested their aircraft design in a rudimentary wooden tunnel with a fan at one end and a test chamber at the other. This allowed them to measure lift and drag on their model aircraft.
A wind tunnel permits the study of the effect of air moving over an object. Rather than moving the object through the air, the wind tunnel moves the air over the object, making this a great example of the Principle 13 – The Other Way Round.
Modern wind tunnels
The Wright brothers placed their fan at the entrance of the tunnel, which meant that the test models were in swirling air from the fan blades. Current wind tunnel design places the fan after the test chamber to prevent this – more Principle 13 thinking.
Modern wind tunnels can be much larger and more powerful and designed to produce smooth, laminar flow. To permit greater efficiency, today’s wind tunnel are closed-circuit facilities. This means they run the air in a continuous loop, preserving some of the kinetic energy of the air as it travels around. This also makes it easier to maintain consistent testing conditions (temperature, humidity).
Tunnels employ vanes to direct the air into predictable bands, creating smooth, laminar flow. To avoid skewing results due to asymmetric flow, double-return wind tunnels route into two return tunnels, splitting the flow from the test chamber into tunnels to the left and the right and then merging it in front of the test chamber. Principle 1 – Segmentation
