Slippery shapes

When it comes to optimising aerodynamics, it’s the little things that make the biggest difference.

Cd figure 0.24 – when it comes to aerodynamics, the new Audi A6 is at the very forefront of the business class.

Johannes Kobler

Bernhard Huber

5 September, 2018


Lower fuel consumption and higher speed – finely tuned aerodynamics deliver major benefits in everyday driving and the new Audi A6 which is due in Australia in the new year is right at the forefront with a drag coefficient of just 0.24. 

Audi aerodynamicist, Andreas Lauterbach, explains why his field of work is so important. 

“Drag increases proportionately with speed squared. When a car is driving at 130km/h on the autobahn for example, it already needs more than 50 percent of its drive energy to overcome drag. And that figure rises substantially as speed increases. That’s why even the tiniest detail matters in aerodynamics. A reduction of one hundredth in the cd figure lowers CO2 emissions on the autobahn by around four grams per kilometre.” 

So, what are those details? A crucial field in aerodynamics is the car’s underbody and airflow around the wheels. Added together, this makes up for around 40 percent of overall drag, which is why it’s particularly important to incorporate aerodynamics into the development process from the very start. The wheels have a major influence, as Lauterbach explains: 

“On some European markets for example, we are offering 17 and 18-inch wheels with aerodynamically optimised designs for the new A6. Here, too, tiny details have a considerable impact on the wheel’s aerodynamic characteristics.” 

When a car is driving at 130km/h on the autobahn for example, it already needs more than 50 percent of its drive energy to overcome drag

Even the dynamic deformation of the tyre while driving and the impressions on its flanks play a measurable role

 

Even the dynamic deformation of the tyre while driving and the impressions on its flanks play a measurable role according to the expert. 

“A further significant area is the underbody cladding,” says Lauterbach. “We’ve closed in the engine compartment, the centre of the underbody on either side, the fuel tank and the SCR tank.” The rear suspension control arms are also clad, while the airflow is directed by small inflow bodies and spoilers in front of the front wheels. 

Extensive fine tuning was also carried out on the bodyshell. “One major factor is the exterior mirrors. We put a lot of hard work into their aerodynamic optimisation,” says Lauterbach. “At the rear end, we worked with our colleagues from Design to find good solutions for the spoiler edge and the contours around the lights, which play a role in defining the separation of the airflow.” 

The front end is likewise incredibly important to the way the air flows – the mesh in the Singleframe grille closed off as far as possible from a thermal standpoint, while the outer sections of the air intakes have separate openings. 

“They divert part of the air inflow through channels into the wheel arches so that it flows smoothly around the wheels,” says Lauterbach.

The new Audi A6 also scores highly in aero-acoustics, too – justifying its best-in-class positioning. The highly sophisticated concept for the sealing around the doors is the result of close collaboration with development engineers, with Audi delivering optional acoustic glazing for all windows except the rear window. 

The exterior mirrors are also an aero-acoustic highlight, according to Lauterbach: 

“By carefully shaping them, we were able to reduce the noise level considerably compared with the previous model.” 

The overall noise level on board is extremely low – with high-speed performance proving a particular differentiator. “In the new A6, the driver and passenger can easily hold a relaxed conversation even at 180km/h,” says Lauterbach. And while those speeds may not be an issue on Australian roads, the benefit to cabin insulation at local cruising speeds will be obvious when the car arrives next year.

“In the new A6, the driver and passenger can easily hold a relaxed conversation even at 180km/h,” says Lauterbach