Let it snow: Scania's tunnel can recreate even the most extreme conditions
If the measure of an engineer is the size of their tools, then an on-site climatic wind tunnel gives you something to be proud of. Christer Ramdén, head of vehicle performance testing at Scania, clearly likes his wind tunnel. It’s new, it’s bigger than most other people’s, and it makes snow, rain and sunlight. But best of all, it saves him, and his Swedish truck-maker employer, time and money. “Doing field tests can take a long time,” he says. “You have to wait for the right conditions. Here, we can push a button to get the weather we need.”
Climatic wind tunnels can simulate the various environmental conditions found around the world: snow, rain, wind and heat. They’ve been used by automotive engineers for decades to test that their vehicles can operate in extreme conditions. The tunnels have become increasingly advanced, to the point where they can now recreate weather from a snowstorm at the top of a mountain to a tropical downpour at the push of a button.
The tunnels have a large fan to create wind, positioned behind a nozzle that can usually be adjusted or changed according to the size of the vehicle and wind speeds required. To simulate weather conditions, they can be equipped with a dyno under the vehicle and with plant and equipment such as light arrays, lamps, snow machines, refrigeration units and sprinklers.
Traditionally, a climatic wind tunnel’s main use is to assess passenger comfort under hot and cold conditions, and to test the performance of vital components, such as the powertrain or braking systems, under extreme conditions. Aspects such as the flow of rain across a windscreen onto side windows and mirrors are also checked and optimised.
Scania’s tunnel at its Sondberg site was opened in July last year, and is the newest in Europe. As Ramdén ushers us through the 20m long test chamber, the heat and humidity from the latest test hits, at odds with the Nordic cold outside. The plant can vary the temperature in the test chamber between -35 and +50°C and the humidity between 10 and 95%. The tunnel has a ‘sun array’, which allows the temperature to be changed by 20°C either way within an hour.
We then move ‘backstage’ into the innards of the machine, which are no less impressive. The tunnel is housed in a multi-storey building the size of a town centre car park. Behind the test chamber and above it are rooms filled with insulated steel pipework, refrigeration units and a massive insulated duct that feeds down into the 4m wide fan, which has 18 carbon fibre blades.
The amount of plant required to recreate weather conditions at a touch of a button is large and expensive. Scania’s new tunnel cost £38 million. The standout feature is its large nozzle which, with a surface area of 13m2, is bigger than the trucks themselves. The dyno, at 800 kW, is also more powerful than those in other wind tunnels. The facility is staffed by a dedicated team of five people, who test up to three trucks a week. Most recently, engineers have been working on a project to adapt Scania trucks to withstand the harsh environments found in mines, as part of a contract with off-highway vehicle supplier Terex.
However, no matter how advanced the technology to recreate environmental conditions gets, there are still limits. “You are doing a simulation of the real thing, but it is still a compromise. The airflow deteriorates as it progresses along the vehicle, so we redirect it so the pressure distribution is consistent,” says Ramdén.
The Scania tunnel joins several that have been opened in the past 10 years, as vehicle manufacturers realise that these engineering assets, despite being expensive, can provide value across multiple products over a long period.
The operators of these climatic wind tunnels get the opportunity to exchange ideas in a group that was set up in 1990. The Climatic Automotive Windtunnel Association (CAWA), which covers just the automotive sector in Europe and has 31 members, meets regularly – but to discuss only the facilities, never the vehicles being tested.
Not only is the capital investment for a climatic wind tunnel large, but the operating costs can also be substantial. Michael Steup, chairman of CAWA, works on wind tunnels for Ford in Germany. “A fan drive itself normally requires up to 2MW, and then there is the plant to make the weather and cool or heat the air,” he says.
But the benefit remains the tunnel’s capability to recreate weather conditions “at the push of a button”, he says. Visiting northern Europe, for example, to test for winter conditions is expensive, and the weather may be not quite right or you may run out of time. But a climatic wind tunnel gets round these problems, says Steup. One automotive company has stated that it has been able to replace a 14-day trip to the north to simulate winter conditions with just 14 hours in a climatic wind tunnel.
A ‘regular’ wind tunnel tests for aspects such as the drag coefficients of the entire vehicle and the aerodynamics of the outside appearance, and hence fuel consumption. By contrast, a climatic wind tunnel strives to simulate environmental conditions. Recent innovations in climatic wind tunnels include an improved aerodynamic simulation: increased nozzle size and implementation of boundary layer reduction systems. In addition, some facilities have upgraded the speeds of their drive systems as the speed of vehicles have increased.
“All wind tunnels want to reach higher speeds, and some have installed sensors and systems to measure fuel consumption,” says Steup. “Some facilities are simulating altitude conditions to consider the lower air pressure at more than 3,000m above sea level.”
The facilities have to match the pace of vehicle change, he says. “A facility has to be kept up to date. Fifteen years ago, the dream for engineers was electric and hydrogen vehicles. Now they are on the streets. Facilities weren’t engineered for vehicles with wheel hub motors – they’ve had to be changed.”
There are two groups of wind tunnels, those that belong to and are used exclusively by vehicle OEMs, and those that are provided by engineering test service companies. Car manufacturers’ tunnels are usually not open to the market.
Automotive engineering and test company Mira, based in Nuneaton, Warwickshire, has one of just two climatic wind tunnels in the UK. Mira hires out use of its wind tunnel facilities, alongside advice and consultancy from its engineers, to vehicle manufacturers .
Jeff Stevens is principal engineer of environmental and aerodynamics test at Mira, managing several test facilities. The site has two climatic wind tunnels. The larger and more advanced opened in 2006. It is 19.5m long, 8m wide and 6m high and has a floor loading of 62 tonnes, making it big enough to hold a double-decker bus. It features a dyno, refrigeration plant and equipment to make rain and snow. It can simulate speeds up to 180km/h when the smallest nozzle is used.
The facility is used by all types of vehicles, says Stevens. “We are independent, so we have to accommodate a wide variety of vehicles – and sometimes not even vehicles. We’ve had Prince Harry in here overnight, and Bear Grylls when he did his Everest Challenge. But the variety also means that the environment in the test chambers is constantly changing.”
One of the main challenges is the constant upgrading of the facilities required because Mira’s wind tunnels are in use seven days a week, says Stevens. This upgrading can also be driven by regulation. The tunnels use a two-stage system, with R22 as its refrigerant. But this substance has recently been banned by the EU, and Mira will have to both buy the new working fluid and overhaul the plant to handle it.
Climatic wind tunnels normally have a lifespan of up to 30 years. With computer simulation technology constantly advancing, it’s tempting to see these facilities as being of their time – filling a gap between computers and physical testing. However, Stevens sees climatic wind tunnels and simulation software, such as Computational Fluid Dynamics (CFD), as complementary. “You won’t get rid of climatic wind tunnels,” he says. “We’ve got the hardware and software at Mira, and we work hard to correlate the two. Nowadays, it’s closer than ever, and CFD is a good tool. But it can’t completely substitute for a wind tunnel.”
Steup from CAWA agrees, and does not envisage the need for climatic wind tunnels in the automotive sector diminishing. The past few years have seen huge investments from European OEMs, and further investments are planned or in progress, he says.
“Companies will continue to need a combination of computer simulation and physical testing. Programming and running a simulation can take weeks. Often the cheapest and fastest option, especially with rain, snow and altitude, is to put a vehicle in the wind tunnel. You can set the vehicle and tunnel up, and have results the same day. Wind tunnels can be used to refine computer models.”
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