A wind tunnel is a research tool developed to assist with studying the effects of air moving over or around solid objects.
Air is blown or sucked through a duct equipped with a viewing port and instrumentation where models or geometrical shapes are mounted for study. Various techniques are then used to study the actual airflow around the geometry and compare it with theoretical results.
Threads can be attached to the surface of study objects to detect flow direction and relative speed of air flow.
Dye or smoke can be injected upstream into the airstream and the streamlines that dye particles follow photographed as the experiment proceeds.
NASA wind tunnel with the modell of a plane
A vertical wind tunnel is a recreational facility for indoor skydiving.
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2 Well known wind tunnels around the world
3 External references:
History of Wind Tunnels
Before the Wright brothers' innovation of the wind tunnel, scientific studies of aerodynamics had been carried out using a "whirling-arm apparatus" first developed by Sir George Cayley in the 1800s.
The Wright brothers, working with Octave Chanute invented and built a simple wind tunnel in 1901 to study the effects of airflow over various shapes while developing their revolutionary Wright Flyer. The Wright wind tunnel was used more recently to test modern low-speed fliers, such as the human-powered "Albatross".
Subsequent use of wind tunnels proliferated as the science of aerodynamics and discipline of aeronautical engineering were established as air travel and power were developed.
Early wind tunnels were often limited in the volume and speed of airflow which could be delivered.
The wind tunnel used by German scientists at Peenumunde prior and during WWII is an interesting example of the difficulties associated with extending the useful range of large wind tunnels. It used some large natural caves which were increased in size by excavation and then sealed to store large volumes of air which could then be routed through the wind tunnels. This innovative approach allowed lab research in high speed regimes and greatly accelerated the rate of advance of Germany's aeronautical engineering efforts.
Later research into airflows near or above the speed of sound used a related approach. Metal pressure chambers were used to store high pressure air which was then accelerated through a nozzle designed to provide supersonic flow. The observation or instrumentation chamber was then placed at the proper location in the throat or nozzle for the desired airspeed.