Aerodynamic tunnel or Wind tunnel , are used to study the aerodynamic efficiency of a vehicle. Aerodynamic designs reduce roll resistance in cars or planes . In aeronautics , a research device that simulates the conditions experienced by an object moving through the air . In an aerodynamic or wind tunnel, the object remains stationary while the passage of air or gas is forced above it.
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- 1 History
- 2 Use
- 3 Definition
- 4 types
- 1 Open Tunnel
- 1.1 Parts of the open tunnel
- 2 Closed Tunnel
- 1 Open Tunnel
- 5 Other types
- 1 F / A-18 real in giant tunnel (NFAC)
- 6 Size and Capacity
- 7 Special Tunnels
- 8 How the wind tunnel works.
- 9 Measurements being made
- 10 Models that are tested
- 11 Sources
The English military engineer Benjamin Robins (1707-1751) invented a rotary arm apparatus to perform resistance experiments within aviation theory.
George Cayley (1773-1857), also used a rotary arm to measure the resistance and lift of various blades. Its swing arm was 5 feet long and achieved tip speeds of between 10 and 20 feet per second. Armed with data from arm tests, Cayley built a small glider believed to have been one of the first heavier-than- air vehicles that was successfully used to carry a man in history. However, the rotating arm does not produce an air flow that impacts the test forms at a normal incidence. Centrifugal forces and the fact that the object is moving through its own wake mean that a detailed examination of air flow is difficult.
Francis Herbert Wenham (1824-1908), a Member of the Council of the Aeronautical Society of Great Britain , fixed these problems, designing and operating the first aerodynamic tunnel in 1871 . A wind tunnel, known as an “aerodynamic tube” was designed and built by Ziolkovsky in 1897. Once this discovery came to light , detailed technical data was quickly extracted. Wenham and his colleague Browning are credited with many fundamental discoveries, including revealing the beneficial effects of a high aspect ratio.
Carl Rickard Nyberg used an aerodynamic tunnel when designing his Flugan in 1897. In experiments, the English Osborne Reynolds (1842-1912) from the University of Manchester showed that the pattern of air flow on a scale model would be the same for the real vehicle. if a certain flow parameter were the same in both cases. This factor, now known as the Reynolds Number, is a basic parameter in the description of all fluid-flow situations, including the shapes of flow patterns, the ease of heat transmission, and the presence of turbulence.
The Wright brothers in 1906 managed to fly their prototype “Flyer” on Kitty Hawk Beach. Before making these flights, they made several tests with gliders and models.
For the determination of the wing profiles (shape of the wing profile, the transverse direction) they studied the Otto Liliental models and carried out tests in a home-made wind tunnel. This tunnel was very simple and rustic, but useful enough to be able to determine that certain forms of wing profiles produced a stress perpendicular to the wind speed and upwards (lift force), which would help to lift the airplane.
Subsequently, aerodynamic tunnels were used as part of aerodynamic science and aeronautical engineering disciplines, and travel and air power were developed. Aerodynamic tunnels were often limited by the volume and speed of the air stream that could be delivered. The aerodynamic tunnel used by German scientists at Peenemünde during World War IIIt is an interesting example of the difficulties associated with extending the useful range of an aerodynamic tunnel, where natural caves were used is that they were increased in size by excavation and then sealed to save large volumes of air that could be redirected through the tunnels. This innovation enabled research into high speed regimes and accelerated the ratio and efforts of German aeronautical engineering , making it possible for Germany to be the first to commission jet fighters. The first supersonic wind tunnel was built in Germany, with a power of 100,000 horses steam . After World War II, it was dismantled and moved to America .
These tunnels are used to study the effects of the movement of the air on objects such as aircraft , spacecraft, missiles, cars , buildings or bridges.
A wind tunnel or aerodynamic tunnel is an experimental tool to study the effects of air flow on objects or solid bodies.
It is a tube-shaped installation through which a mass of air circulates around the solid or object of study.
There are 2 types of wind tunnels: open and closed.
The air enters from the outside into the tunnel, and once it has traveled it returns to the outside.
Parts of the open tunnel
- Establishment chamber: Its objective is to straighten and standardize the air flow.
Acceleration cone: Its function is to compress the air and accelerate the flow velocity to lead it to the test chamber.
- Test chamber: Place where the model we want to study is located and where the measurements are made.
Diffuser: Once the air has already left the test chamber, the diffuser reduces the flow velocity through its diverging profile. We are interested in the air leaving at the lowest possible speed since the exit speed will be related to the energy losses of the tunnel. The slower the speed, the lower the losses. Fan: It is the force that drives the air flow.
Unlike the previous one, the closed tunnel recycles the air in a cyclical way, thus allowing the thermodynamic variables of the air to be controlled: density, temperature and pressure. This type is more complex and expensive, since a series of baffles have to be installed along the tunnel to keep the flow controlled and avoid turbulence.
According to their size : There are small wind tunnels to test scale models and there are colossal tunnels that are capable of housing up to a real plane such as NASA’s National Full-Scale Aerodynamics Complex (NFAC).
Real F / A-18 in giant tunnel (NFAC)
According to the speed they reach:
- Subsónco tunnel (Mach <1)
- Transonic Tunnel (Mach = 1)
- Supersonic Tunnel (Mach> 1)
- Hypersonic Tunnel (Mach> 5)
Depending on how the air is blown:
- Blowing: The fan is in front of the model, it provides more speed but the flow becomes turbulent.
- Aspirated: The fan is behind the model, it provides less speed but the flow is laminar.
There are also a type of vertically arranged aerodynamic tunnels for parachute training.
Size and Capacity
The size of the aerodynamic tunnels range from a few centimeters to 12 m × 24 m in the tunnel of the Ames Research Center in Moffet Field ( California , USA ), belonging to NASA . This huge wind tunnel can accommodate a real plane with a wingspan of 22 meters.
The larger the tunnel cross section, the more difficult it is to create and maintain high- speed air flows . This problem is very large in supersonic and hypersonic tunnels, where the power needs are so great that the tunnel size has to be much smaller. Although motor driven fans may be used in a large, low-speed wind tunnel, higher speeds require the use of air compressors , the release of pressurized stored gas, or the explosive discharge of gases. Aerodynamic tunnels powered by a gas charge can only operate for a short period of time. In the hypervelocity tunnel of the Ames Research CenterVery high speeds are obtained by propelling small models of airplanes or spacecraft using an explosive charge, while simultaneously another explosive charge launches gas into the tunnel in the opposite direction. Under these conditions, relative speeds of almost 50,000 km / h can be achieved for one second.
During supersonic spacecraft flight, friction generates a significant amount of heat. To study these effects, special aerodynamic tunnels are used in which a jet of hot gases flows over the model of the vehicle while a series of instruments measures the movement of the gas and the generation of heat.
Smoke is sometimes injected into low- speed tunnels to make air movement visible on the wings of an airplane. Other tunnels allow you to simulate high altitudes and observe their influence on the performance of an airplane. Altitudes of up to 145 km have been simulated. These high-altitude tests are also very important in predicting the performance of a reactor in any flight condition. Tunnel the Flight Propulsion Laboratory of NASA in Cleveland ( Ohio), it can test real reactors with speeds of up to 3,900 km / h and altitudes of more than 30,000 meters. The European Transonic Aerodynamic Tunnel, to be used by European aerospace companies and research centers, will have a similar capacity.
How the wind tunnel works.
The airit is blown or sucked through a duct equipped with stabilizing grids at the beginning to ensure that the flow behaves in a laminar way or with obstacles or other objects if it is desired to behave in a turbulent way. The models are assembled for their study in a team called a scale to which are attached the sensors that provide the necessary information to calculate the coefficients of lift and resistance, necessary to know if it is feasible or not to use the model in real life. In addition, other devices are used to record the difference in pressure on the surface of the model in question. The practical results must be compared with the theoretical results,
The measurements that are made
During the aerodynamic test , various techniques are used to analyze the collected data, most of which are processed by computer using the technology known as Computational Fluid Dynamics.
There are also flow visualization techniques such as:
- Strands can be attached to the study surface to detect the direction of airflow and its relative velocity .
- Dyes or smoke can be injected into the air stream to observe the movement of the particles as they pass the surface.
- Probes can be inserted at specific points in the air flow to measure static or dynamic air pressure.
Models being tested
In wind tunnels, it is mostly experimented with cars and airplanes , especially in Formula 1 where aerodynamics is a crucial factor to configure the car in optimal conditions for the race. However in the wind tunnels cyclists, skiers, swimmers and even birds and insects are also tested to study their flight.