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In tunnels, in snow and rain or at freezing temperatures many miles above sea level: Automobiles and airplanes have to deliver safe and trouble-free performance in all weather conditions and climatic wind tunnels are the key to success in this case. They help engineers to clearly accelerate their development work.

by Alexander von Wegner  December 2018

As diverse as our means of transportation may be, the expectations of travelers are always the same: getting from A to B as safely and comfortably as possible – be it at –30 °C (–22 °F) and glacial wind at the North Cape or at 40 °C (104 °F) and 95 % relative humidity in the tropical heat of Singapore, be it in passenger cars or trucks, or on buses or airplanes.

 

But how can engineers prepare themselves for such scenarios other than by following the textbook in designing their vehicles and subsequently testing them locally? Climatic wind tunnels are the answer. Modern facilities can be set to temperatures ranging from –40 °C (–40 °F) to 60 °C (140 °F) in some cases. Water sprinkler systems combined with wind speeds of 200 km/h (124 mph) and more simulate hurricanes and even snow can easily be produced in a climatic wind tunnel, as well as 1,200-watt heat per square meter (11 square feet) which equates to solar radiation of about 50 °C (122 °F) similar to the intensity of the Sun in desert regions. The engineers can even vary humidity – tropical conditions are reached at 95 percent.

 

Ford’s wind tunnel test center that was opened in 2018 can even “climb mountains.” As the first of its kind to do so, the facility simulates elevations of up to 5,200 meters (17,060 feet). For Ford, this is a huge advantage: The automaker, according to its own account, sells more than half of its vehicles to regions located more than 1,000 meters (3,281 feet) above sea level.

 

80 % less road testing

 

The pictures delivered by the tests, both on the road and in the wind tunnel, are impressive. In cold testing, massive sheets of snow and ice form on the vehicle bodies and in front of the grilles and air scoops. Is the cooling system still functioning? Will the engine start? How long will it take the heater to warm up the cabin and to defrost the windows? How long will it take the air conditioning system to cool down a hot interior? How will the windshield wipers perform? Will plug connections and electronic equipment function flawlessly even in conditions of arctic cold and extreme heat?

 

In their pursuit of answers, the developers could test on roads around the globe for months on end: a major logistical feat. An additional difficulty lies in the fact that natural weather phenomena are hardly controllable and repeatable. This is precisely why the climatic wind tunnels are so valuable for manufacturers: They make it possible to clearly accelerate development cycles. General Motors, for instance, says a climatic wind tunnel is able to reduce road testing by 80 percent. Volkswagen emphasizes that the communication channels between development teams such as vehicle safety, design, acoustics and comfort are significantly shortened. Aircraft manufacturer Boeing has been operating an icing wind tunnel since 1991. Previously, aircraft in their certification process had to prove the absence of icing in 60 to 70 flight hours whereas only eight hours are required in the Boeing Research Aerodynamic Icing Tunnel (BRAIT) where wind speeds of 463 km/h (288 mph) and temperatures of 0 °C (32 °F) to –30 °C (–22 °F) are possible.

 

Climatic wind tunnels, however, are not only important in automotive engineering and aviation. The larger of the two wind tunnels of the Rail Tec Arsenal (RTA) in Vienna, Austria, is so voluminous on a 100-meter (328-foot) test section that it can accommodate a train unit with several cars. The aircraft industry uses the massive facility as well. Helicopters and small aircraft as well as 3.5 meter (11.5 feet) wing segments fit into the huge tunnel in Vienna’s Floridsdorf district. The facility is even able to generate cumulus and stratus clouds.

 

The consumer benefits as well

 

Be it acceptance or approval tests in aviation, sophisticated large-scale air conditioning systems like those of trains or the perfect climatic suitability of an automobile: When all the components have also been put through their climatic paces, people will travel in safer, more consistent and more reliable conditions. Interiors featuring enhanced comfort please their passengers with optimized heating, air conditioning and ventilation. When companies test their products in climatic wind tunnels and optimize the fuel economy of individual assemblies and thus entire vehicles this results in higher energy efficiency as well. Consequently, the thermal tunnels make an important contribution to safety, comfort and environmental protection in many industrial sectors.

Audi

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    Audi makes its wind tunnel available to partners from the sports arena as well. Among other athletes, skiers and sailors optimize their game with the wind there

    At Audi, a climatic wind tunnel was added in early 2008 to complement the Wind Tunnel Center in Ingolstadt. Its thermal range extends from –25 °C (–13 °F) to 55 °C (131 °F). A 2.4-megawatt fan generates wind speeds of 300 km/h (186 mph) across the ten-meter (33-foot) test section. Sunlight of up to 1,200 watts per square meter (11 square feet) and rain simulations of 2,500 liters (660 gallons) per hour simulate extreme weather situations under laboratory conditions. For cars with all-wheel drive, a dynamometer is available for each axle with respective output of 250 kW (340 hp). Even the Audi R18 TDI race car was tested in this wind tunnel in 2011. For the 24 Hours of Le Mans and other races, the engineers wanted to know how effectively the cockpit was ventilated, how the windshield worked and where dirt settled on the windshield.

Ford

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    Ford’s Environmental Test Center is a state-of-the-art facility combining all weather conditions under one roof.

    In May 2018, Ford opened a new Climatic Wind Tunnel Test Center in Cologne-Merkenich with a temperature range from –40 °C (–40 °F) to 55 °C (131 °F). Wind speed of 250 km/h (155 mph) represents a category 5 hurricane. The facility is able to generate up to 95 percent humidity, the solarium operates with up to 1,200 watts per square meter (11 square feet). It’s the first automotive climatic wind tunnel that’s capable of simulating elevations of up to 5,200 meters (17,060 feet). In addition to engine cooling, Ford uses this capability to test cold starting performance and the functionality of automotive fluids in extreme air pressure conditions. The engineers are able to simultaneously test up to ten vehicles. The facility has a capacity of 11 megawatts – enough to supply a town with a population of 2,400 with energy. Ford relies on renewable, certified energy sources from Scandinavia at the wind tunnel test center.

RTA

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    100 meters (328 feet) long and temperatures down to –45 °C (–49 °F) – RTA in Vienna is one of the world’s largest climatic chambers

    Rail Tec Arsenal (RTA) is specifically designed for climatic tests of rail vehicles. However, passenger cars, buses or trucks can also be tested in the climatic wind tunnel facility that was built from scratch in 2003 and is equally suitable for aircraft. Manufacturers of other products test their technical systems there as well. For instance, weather conditions and wind loads can be simulated for façade segments, for traffic engineering such as signal and transmission systems, railroad switch systems, wind protection walls or for wind turbines or transformers in energy engineering, etc. As an accredited test institute RTA is also able to conduct climate-specific compliance investigations according to international standards. The temperature range extends from –45 °C (49 °F) to 60 °C (140 °F) and humidity can be varied between 10 and 98 percent. An overhead rain rig and an icing rig, a spray rig and mobile snow nozzles simulate wetness and ice. Since 2013, the facility has been able to even generate cumulus and stratus clouds: 260 nozzles vaporize water with compressed air into icy droplets. The small wind tunnel enables 120 km/h (75 mph) of wind speed and has a 33.8 meter (110 foot) long test section with a frontal area of up to 28.7 square meters (301 square feet). The large wind tunnel is designed for 300 km/h (186 mph), its 100 meter (328 foot) long test section can even accommodate a train set and the frontal area has a size of up to 32.2 square meters (347 square feet).

Volkswagen

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    In Wolfsburg, a new Wind Tunnel Efficiency Center in an area of 8,800 square meters (95,000 square feet) was opened in 2017. The research center has a new thermo-functional tunnel and a combined aerodynamics and aero acoustics tunnel. The temperature range extends from –30 °C (–22 °F) to 60 °C (140 °F). Wind speed reaches 250 km/h (155 mph) and humidity can amount to as much as 95 percent. The roller dynamometer enables tests of vehicles with output of up to 1,000 kW (1,360 hp). The fan in the thermo-functional tunnel has a diameter of 4.5 meters (14.8 feet) and consumes 2.1 megawatts. When Volkswagen made history with a first thermal wind tunnel in 1965, performance ratings were clearly different: It took 2.6 megawatts to achieve the maximum speed of 150 km/h (93 mph) (and even that was 30 km/h (19 mph) faster than a hurricane) and the thermometer reading did not rise above 45 °C (113 °F). Therefore, a second generation of the facility, the thermo-functional tunnel 2, was built in Wolfsburg. However, it no longer met the constantly growing demands anymore either – so now there’s a third generation.

In the eye of the storm

Cross section of the Mercedes-Benz climatic wind tunnel in Sindelfingen, Germany.

Mercedes-Benz

The Stuttgart-based automaker has a cold tunnel for the temperature range between –40 °C (–40 °F) to 40 °C (104 °F) and a warm tunnel for the range between –10 °C (14 °F) and 60 °C (140 °F). Thanks to two-axle roller dynamometers and speeds of up to 265 km/h (165 mph) even sports cars can be tested. Mercedes-Benz does not view the facilities as a substitute for road testing but as offering the major benefit of clearly reducing the number of road tests and being able to approach them with far better preparation. Variants of individual components can already be rejected under laboratory conditions. The acceleration is tangible because the engineers no longer have to conduct lengthy preliminary road tests. Even so, the resulting technical maturity of the prototypes is higher. In addition to vehicles with IC engines, the company can test models with fuel cells in its climatic wind tunnels. Air conditioning, ventilation or component tests are equally in focus as the simulation of long downhill driving in high summer temperatures in order to test the loads acting on the braking system. Even road surface heat can be set to temperatures between 50 and 70 °C (122 °F and 158 °F) in order to take this real-world factor into account as well.

The front view in the cross section reveals the two side-by-side climatic tunnels “warm” (–10 to 60 °C / 14 to 140 °F) and “cold” (–40 to 40 °C / –40 to 104 °F)

From the Eiffel Tower to the climatic chamber

A free fall precedes the first wind tunnel: Gustave Eiffel is one of the first engineers to get to the bottom of aerodynamics. In 1905, he has various metal plates dropped from the second platform of the tower that’s named after him (pictured). Although the tests deliver convincing results, the method heavily depends on the prevailing weather conditions. That’s why, in 1909, Eiffel moves to the Laboratoire Aerodynamique Eiffel that he designed himself – a type of open wind tunnel that aspirates outside air via a turbine – including ambient temperature and pressure fluctuations. Consequently, precision soon reaches its limits.

The situation with the test method developed by the German engineer Ludwig Prandtl (pictured) at roughly the same time is different. In his investigation of fluid dynamics, Prandtl uses a closed circuit in which air is accelerated. His results are not only more precise but the tests are repeatable as well. This design soon evolves into an international standard. Even today, Ludwig Prandtl is still regarded around the world as the “father of aerodynamics.”

At the beginning of the 20th century, research is focused on the fledgling field of aviation. However, after the First World War, more and more automobiles feature streamlined designs too (pictured: Edmund Rumpler’s “Tropfenwagen” (“Drop Car”) from 1921 with a drag coefficient of 0.28 that’s still exemplary today). In 1965, VW in Wolfsburg combines a climatic chamber and a wind tunnel for the first time. The wind and weather simulator would remain a technological trailblazer for many years.

How Schaeffler tests

Schaeffler uses various simulation technologies to test products and accelerate developments as well. In Germany and China, Schaeffler operates special test rigs for wheelset bearings of rail vehicles that simulate speeds of 600 km/h (373 mph) and axle loads of up to 40 metric tons (44 short tons). If necessary, a turbine is able to simulate airflow of up to 35 m/s (115 ft/s). Together with Friedrich-Alexander University Erlangen-Nuremberg (FAU) Schaeffler developed a rolling bearing spin test rig that was taken into operation in 2016. On it, bearings are exposed to 3,000-fold gravitational acceleration and tested under the resulting high loads. The results of this research project are intended to optimize current rolling bearing technology with the objective of reducing the energy consumption of vehicles and machines.

 

The large-size bearing test rig ASTRAIOS (r.) in Schweinfurt, Germany, is a veritable giant. It enables testing of large-size bearings of up to 15 metric tons (16.5 short tons) and an outer diameter of 3.5 meters (11.5 feet) by means of an extensive simulation program under field-like conditions.

 

For the development of the electromechanical roll stabilizer, Schaeffler already used the “test rig of the future,” a joint project with Fraunhofer Institute LBF. In this case, the test environment as well as the product itself is shifted into the computer as a digital twin. This yields a significant reduction of cost-intensive rig testing times and accelerates processes in general because obstacles can be detected and their causes identified early.

Video Credits: Ford; Photo Credits: Audi, RTA, Volkswagen (5), Daimler AG (2), Schaeffler

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    Storage facility for pre-conditioned fuels

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    6 conditioning compartments and an adjacent workshop. This is where the vehicles are prepared and heated or cooled to the desired temperature. Subsequently, the vehicles are taken directly and without external contact to the climatic wind chamber, so the tests can immediately begin there

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    The turbine generates any desired wind up to hurricane intensity (200 km/h) (124 mph). Even at wind speeds of 100 km/h (62 mph) a human being can no longer stand safely

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    In an area of 8 x 2.5 meters (26 x 8 feet) the radiation intensity of 200–1,200 watts/m2 (11 sq ft) can be controlled. A comparable peak value outdoors can only be found at extremely hot locations such as in Death Valley (USA)

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    Test facility accommodating passenger cars/commercial vehicles from the Smart to the Sprinter

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    The so-called “hot road” is continually variable from 50 to 70 °C (122 to 158 °F). It serves to simulate the heat on a road in summer

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    4-wheel roller dynamometer. The total capacity (max. 780 kW) is sufficient for simulated speeds of up to 265 km/h (165 mph)

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    Humidifier (55–95 % humidity)

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    Heating/cooling element with a temperature range from –40 to +60 °C (–40 to 140 °F)

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    Snow/rain simulation. Hourly precipitation of up to 80 l/m2 (21 gal/11 sq ft) can be equally simulated as the worst blizzards in which snowflakes hit the test vehicles at a speed of 200 km/h (124 mph)

Mercedes-Benz

The front view in the cross section reveals the two side-by-side climatic tunnels “warm” (–10 to 60 °C / 14 to 140 °F) and “cold” (–40 to 40 °C / –40 to 104 °F)

  •  

    The Stuttgart-based automaker has a cold tunnel for the temperature range between –40 °C (–40 °F) to 40 °C (104 °F) and a warm tunnel for the range between –10 °C (14 °F) and 60 °C (140 °F). Thanks to two-axle roller dynamometers and speeds of up to 265 km/h (165 mph) even sports cars can be tested. Mercedes-Benz does not view the facilities as a substitute for road testing but as offering the major benefit of clearly reducing the number of road tests and being able to approach them with far better preparation. Variants of individual components can already be rejected under laboratory conditions. The acceleration is tangible because the engineers no longer have to conduct lengthy preliminary road tests. Even so, the resulting technical maturity of the prototypes is higher. In addition to vehicles with IC engines, the company can test models with fuel cells in its climatic wind tunnels. Air conditioning, ventilation or component tests are equally in focus as the simulation of long downhill driving in high summer temperatures in order to test the loads acting on the braking system. Even road surface heat can be set to temperatures between 50 and 70 °C (122 °F and 158 °F) in order to take this real-world factor into account as well.

From the Eiffel Tower to the climatic chamber

  •  

    A free fall precedes the first wind tunnel: Gustave Eiffel is one of the first engineers to get to the bottom of aerodynamics. In 1905, he has various metal plates dropped from the second platform of the tower that’s named after him (pictured). Although the tests deliver convincing results, the method heavily depends on the prevailing weather conditions. That’s why, in 1909, Eiffel moves to the Laboratoire Aerodynamique Eiffel that he designed himself – a type of open wind tunnel that aspirates outside air via a turbine – including ambient temperature and pressure fluctuations. Consequently, precision soon reaches its limits.

    The situation with the test method developed by the German engineer Ludwig Prandtl (pictured) at roughly the same time is different. In his investigation of fluid dynamics, Prandtl uses a closed circuit in which air is accelerated. His results are not only more precise but the tests are repeatable as well. This design soon evolves into an international standard. Even today, Ludwig Prandtl is still regarded around the world as the “father of aerodynamics.”

    At the beginning of the 20th century, research is focused on the fledgling field of aviation. However, after the First World War, more and more automobiles feature streamlined designs too (pictured: Edmund Rumpler’s “Tropfenwagen” (“Drop Car”) from 1921 with a drag coefficient of 0.28 that’s still exemplary today). In 1965, VW in Wolfsburg combines a climatic chamber and a wind tunnel for the first time. The wind and weather simulator would remain a technological trailblazer for many years.

How Schaeffler tests

  •  

    Schaeffler uses various simulation technologies to test products and accelerate developments as well. In Germany and China, Schaeffler operates special test rigs for wheelset bearings of rail vehicles that simulate speeds of 600 km/h (373 mph) and axle loads of up to 40 metric tons (44 short tons). If necessary, a turbine is able to simulate airflow of up to 35 m/s (115 ft/s). Together with Friedrich-Alexander University Erlangen-Nuremberg (FAU) Schaeffler developed a rolling bearing spin test rig that was taken into operation in 2016. On it, bearings are exposed to 3,000-fold gravitational acceleration and tested under the resulting high loads. The results of this research project are intended to optimize current rolling bearing technology with the objective of reducing the energy consumption of vehicles and machines.

     

    The large-size bearing test rig ASTRAIOS (r.) in Schweinfurt, Germany, is a veritable giant. It enables testing of large-size bearings of up to 15 metric tons (16.5 short tons) and an outer diameter of 3.5 meters (11.5 feet) by means of an extensive simulation program under field-like conditions.

     

    For the development of the electromechanical roll stabilizer, Schaeffler already used the “test rig of the future,” a joint project with Fraunhofer Institute LBF. In this case, the test environment as well as the product itself is shifted into the computer as a digital twin. This yields a significant reduction of cost-intensive rig testing times and accelerates processes in general because obstacles can be detected and their causes identified early.