Aerodynamics: The lowest wind noise in the world

Jun 23, 2014
A low interior noise level was a declared objective when developing the new S-Class Coupé. The aeroacoustics experts optimised the exterior form in key areas as early as the design phase. The bodyshell and the door sealing concept, to name but two examples, were configured to further reduce wind noise. With success: the S-Class Coupé not only has a much quieter interior than its predecessor, it is also the quietest series-production car of all in terms of wind noise.
The low interior noise level was a declared development objective as it enhances both comfort on long journeys and driver-fitness safety. The S-Class Coupé not only has a much quieter interior than its predecessor in terms of wind noise, it is also the quietest series-production car of all, as proven by measurements taken in the wind tunnel using an artificial head to simulate the driver's ear and test drives with specially trained test people.
Even when travelling at high speed, it is just as easily possible to enjoy music and phone using the hands-free system as it is to talk to other passengers in the new S-Class Coupé. That's because articulation quality, i.e. speech intelligibility when there are various forms of background noise, is a central criterion in the Aeroacoustics Index. Mercedes-Benz uses this in-house index, developed over the course of long series of tests, to assess wind noise in the vehicle. As people are particularly disturbed by fluctuating auditory impressions, there were also measurements at an oblique inflow angle of up to 20° in the wind tunnel to simulate possible wind noise in the event of crosswinds.
The excellent aeroacoustic performance is not just down to the coupé form and the relatively small surface areas of the up to 6 mm thick windows. Optimisation measures on the bodyshell and the lightweight doors help to reduce low-frequency wind noise. In the easily audible medium-frequency range, the improved insulation enhances acoustic comfort. Optimisation measures have been implemented to reduce high-frequency wind noise, with the focus on the sealing concept for the windows and door handles. However, the exterior mirrors flowing into the doors, their new shape and the correspondingly designed A-pillars with minimised step height prevent an airflow breakaway at these points, and therefore noises that could enter the interior via the windscreen and side windows.
The cd value for the S 500 4MATIC Coupé with standard-fit 18-inch wheels is 0.27 – meaning that the new S-Class Coupé displays the same excellent flow characteristics as the predecessor model. Good flow characteristics play a decisive role in ensuring low fuel consumption under everyday conditions and enhance driving dynamics. The front and rear axle lift, and the balance between the two, have been configured by shaping the vehicle in a way that perfectly matches its sporty aspirations.
The aerodynamic development work was equally extensive and included the implementation of the following measures:
  • Sealing in the vicinity of the headlamps
  • Wheel spoilers with optimum flow ahead of the front wheels
  • Lowering of the vehicle by 10 mm compared to the basic level, as a function of the vehicle speed
  • Optimised underbody panelling concept with large engine compartment and main floor panels to also further minimise the penetration of carriageway noise
  • Large area of cladding on the rear axle.
Safety is enhanced if the windows and exterior mirrors remain free of dirt in the relevant areas in wet weather. Dirt deflection is achieved by suitable channelling of the dirt-laden water that impacts the windscreen, the side windows and the exterior mirrors. On the new S-Class Coupé, the water hitting the windscreen is channelled over the roof by a suitably designed water runnel with continuously decreasing step height and an optimised roof trim strip along the A-pillar.
The shape and water-channelling concept of the new exterior mirrors were likewise optimised with respect to dirt deflection. Thanks to optimisation in the area where the windscreen meets the roof, the areas of the side windows affording a view of the exterior mirrors are kept free of waterdrops. The rear window remains free of dirt up to a speed of approx. 160 km/h.