Development of sustainable vehicles would be not be realistic without the successes of wind tunnel research. With its ultramodern AVZ Wind Tunnel Centre in Munich, the BMW Group has paved the way for a further reduction of up to 30 percent in its vehicles’ aerodynamic drag.
The scene is almost surreal: Four men in helmets fight their way forwards, in as straight a line as possible, one behind the other, heads lowered slightly, muscles straining to the max. They hold this position for about ten minutes, while someone with a fog-spraying nozzle moves closer and closer and an eight-metre-wide turbine subjects them to higher and higher wind speeds of 60, 80, 100 and even 140 kilometres per hour. The team is trying to find the ideal body position that offers the gale-force winds as little drag area as possible. But their primary objective is to test the form and aerodynamics of their vehicle – a bobsleigh that competes in international sporting events like world cups or, most recently, the Olympic Winter Games in Pyeongchang, South Korea. For male and female bobsledders, every hundredth of a second counts. Each little detail can be the difference between gold and silver.
The competitive athletes are making use of the BMW Group’s AVZ Wind Tunnel Centre in Munich to optimise their “arrow”. The 25,000 square-metre AVZ, which cost 170 million euros to build, is one of the most advanced aerodynamic testing facilities in the world, capable of simulating speeds of up to 300 kilometres per hour, with extremely high measurement accuracy.
But, of course, the AVZ’s high tech is mainly used for its actual job of improving the aerodynamics of vehicles with combustion and electric engines – precisely because the adjustments have to be even finer here: Although a bob’s front surface is much smaller – and therefore more like a motorcycle than a car – the drag coefficient (Cd value) is actually slightly higher than the BMW Group’s current models. For example, the latest (seventh-generation) BMW 3 Series has a Cd of only 0.23, while an Olympic bob comes in at 0.3 and higher.
However, even though BMW Group vehicles are already among the best in class, there is still potential for further improvement in the field of aerodynamics: A car body’s aerodynamic drag has a huge impact on fuel economy and a vehicle’s sustainability. The less drag a vehicle creates – because airflow around the car is optimised – the less energy is needed to overcome it.
This is particularly important in further development of electric vehicles. The amount of energy an electric vehicle has at its disposal is much more limited than in a car with a combustion engine, because petrol or diesel have a considerably higher energy density than a high-voltage battery. In some cases, efficiency and the lowest-possible aerodynamic drag are more of a factor than weight – after all, in city driving, an electric vehicle can regenerate much of the starting energy it consumes due to weight the next time it brakes (for instance, at a junction). However, losses due to aerodynamic drag are irretrievably lost.
However, engineers are not just focused on improving aerodynamic drag. They are also working to ensure a precise influx of cooling air to the engine, gearbox and brake system to reduce wind noise and lift, in particular: Due to lift, vehicles driving 200 kilometres per hour may weigh around 120 kilos less at the rear axle alone. They therefore have to be designed in a way that also maintains driving stability at high speeds.
Building on their countless successes so far, such as further improvement of the “ram-air lip” for wheelhouses developed by BMW in the late 80s, engineers expect to further reduce the aerodynamic drag of BMW vehicles over the next few years – in some cases by up to as much as 30 percent – through their work at the AVZ and computer simulations. If successful, this could lower fuel consumption by up to eight percent and help significantly extend electric vehicles’ range. This would not only benefit vehicle sustainability – some of the research findings might also enable bobsledders to go even faster. After all, there’s only three more years until the nextOlympic Games in Beijing.