Wind+Tunnels

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Wind tunnels are tube-shaped facilities that allow engineers to move air over a vehicle as if it were flying. They help researchers to learn more about how an aircraft will fly. Some wind tunnels are big enough to hold full-size versions of vehicles. By moving air around an object, the wind tunnel simulates the conditions of the object in flight. Wind tunnels usually have powerful fans to move the air through the tube. The object being tested is placed in the tunnel so that it will not move. The air moving around the still object shows what would happen if the object were moving through the air. The object can be a smaller-scale model of a vehicle, one piece of a vehicle, a full-size aircraft or spacecraft, or even a common object like a tennis ball. Usually, the object carries special instruments to measure the forces produced by the air on the object. Engineers also study how the air moves around the object by injecting smoke into the tunnel and photographing its motion around the object. Improving the flow of air around an object can increase its lift and decrease its drag.
 * What are Wind Tunnels ?**
 * How Do Wind Tunnels Work?**

The first plane and glider designs had a lot of bird-like characteristics. Wind tunnels proved that many of those ideas were rather bird-brained. Stringer/Hulton Archive/[|Getty Images]

The first wind tunnels were just ducts with fans at one end. These tunnels made choppy, uneven air, so engineers steadily worked to improve airflow by tweaking tunnel layouts. Modern tunnels provide much smoother airflow thanks to a fundamental design that incorporates five basic sections: the settling chamber, contraction cone, test section, diffuser and drive section. Air is a swirling, chaotic mess as it enters the tunnel. The **settling chamber** does exactly what its name implies: It helps to settle and straighten the air, often through the use of panels with honeycomb-shaped holes or even a mesh screen. The air is then immediately forced through the **contraction cone**, a constricted space that greatly increases airflow velocity. Engineers place their scaled models in the **test section**, which is where sensors record data and scientists make visual observations. The air subsequently flows into the **diffuser**, which has a conical shape that widens, and thus, smoothly slows the air's velocity without causing turbulence in the test section. The **drive section** houses the axial fan that creates high-speed airflow. This fan is always placed downstream of the test section, at the end of the tunnel, rather than at the entrance. This setup allows the fan to pull air into a smooth stream instead of pushing it, which would result in much choppier airflow. Most wind tunnels are just long, straight boxes, or **open-circuit** (open-return) tunnels. However, some are built in **closed** **circuits** (or closed return), which are basically ovals that send the air around and around the same path, like a racetrack, using vanes and honeycomb panels to precisely guide and direct the flow. The walls of the tunnel are exceedingly smooth because any imperfections could act as speed bumps and cause turbulence. Most wind tunnels are also moderately sized and small enough to fit into a university science lab, which means that test objects must be scaled down to fit into the tunnel. These scale models might be entire [|airplanes] in miniature, built (at great expense) with exacting precision. Or they might just be a single part of an airplane wing or other product. Engineers mount models into the test section using different methods, but usually, the models are kept stationary using wires or metal poles, which are placed behind the model to avoid causing disruptions in the airflow They may attach sensors to the model that record wind velocity, temperature, [|air pressure] and other variables. Keep reading to learn more about how wind tunnels help scientists piece together more complicated aerodynamics puzzles and how their findings spur technological advances.

http://science.howstuffworks.com/wind-tunnel3.htm to make airflow visible, scientists rely on various **flow visualization** techniques. They may fill the test section with colored smoke or a fine mist of liquid, such as [|water], to see how air moves over the model. They may apply thick, colored oils to the model to see how the wind pushes the oil along the model's surface.

Winds tunnels are used to study the flow of air around an object. An object is placed in a tunnel and subjected to varying wind speeds to determine how it is affected by wind current. Airplanes and rockets are tested in large wind tunnels. Building your own wind tunnel can illustrate how wind speed affects an object and provide a better understanding of flight and aerodynamics.