For increased range, safety, and comfort.

While the flow behaviour was optimised in early development phases using models in the old wind tunnel in Untertürkheim, this fundamental work is now carried out exclusively with simulation. Already at an early stage, the three-dimensional flow field that fundamentally surrounds vehicles is calculated on high-performance simulation clusters using CFD (Computational Fluid Dynamics).

Shortly after the start of the project, in the phase of the dimensional concept, several extensive DOE (Design of Experiments) studies with up to 250 calculations per study are usually carried out based on the predecessor. The aerodynamics engineers specify the parameter space of certain components, e.g. for the possible height of the trunk lid.

Such a DOE investigation takes several days and completely covers the specified parameter space. Based on these simulations, a global or local optimum can then be calculated, or, much more importantly in this phase, the influence of the individual parameters and their mutual dependencies on air resistance can be determined. With the help of the DOE method, concrete aerodynamic requirements can be reported back to and discussed with the employees in the area of dimensional concept as well as with the design department at this very early stage.

In recent years, the aerodynamics experts at Mercedes-Benz have intensively further developed the automated calculation processes including DOE. The path to the aerodynamics world record of the EQS required several 1,000 calculation runs in the virtual wind tunnel with approximately 700 CPU cores per calculation.

In aeroacoustic development, Mercedes Benz always works on two tracks: On the one hand, as little noise as possible should be generated at the source, i.e., when the air flows around the vehicle's outer skin with all attachments. As early as the early development phase of a new model, the engineering team therefore begins to design the geometry dimensions that are particularly relevant for this, for example on the A-pillars and the exterior mirrors.

The pre-design is carried out using a Computational Fluid Dynamics (CFD) simulation, with detailed simulations on the particularly critical vehicle areas and with the help of our own 1:1 hard models in the aero wind tunnel. In combination with an array consisting of 350 microphones, local sound sources on the vehicle's outer skin can be made visible in three dimensions. In this way, even the smallest details in important areas can be developed at an early stage.

On the other hand, the quality of the sealing and sound insulation makes a decisive contribution to ensuring that unavoidable wind noises are no longer perceived or are not perceived as disturbing in the interior. A basic prerequisite for a low wind noise level in the interior is wind-tight door and window seals. This applies in particular to vehicles with frameless side windows. With artificial heads, even the smallest weak points can be specifically located, which are then eliminated as best as possible by technical solutions.

Some car magazines use a sound pressure level meter for tests. However, such measurements only incompletely reflect reality, because the human ear is a master of localising disturbing noises. Mercedes Benz therefore also specifically investigates the psychoacoustically relevant effects and the localizability of disturbing noises. Based on tests with test subjects, the company's experts have even defined their own target index. Its weighted measured variables cover the entire frequency spectrum of human hearing. For example, the following variables and their effects are given consideration:

• Loudness [sone]: Representation of human loudness perception;
• Sharpness [acum]: Classification of noises from dull to sharp, higher-frequency components significantly influence the sharpness;
• Articulation index AI [%]: Speech intelligibility, focusing in particular on the area of best human hearing. The higher the value, the better conversations can be held and understood.

The measurements are usually carried out in the wind tunnel with so-called binaural artificial heads. There, the microphones sit in simulated ear canals, which allows for ear-accurate recordings. Depending on the phenomenon being investigated, the artificial heads sit in the driver's position or take a seat on the other seats in the vehicle. The measurement results then provide a realistic indication of how loud or quiet, disturbing or pleasant the passengers perceive the noise in the interior.

Having the cleanest possible windows and exterior mirror glass and thus optimal visibility under all conditions serves active safety. For this reason, the aerodynamic discipline of keeping the vehicle clean has always enjoyed special attention at Mercedes Benz. In order not to burden the highly sensitive measuring technology and the running belts of the aeroacoustic channel in Sindelfingen with contamination tests, these are still carried out in the “Large Wind Tunnel” in Untertürkheim.

Pollution can be caused by rain, vehicles in front or droplets whirled up by the vehicle's own wheels. In the wind tunnel, this contamination is made visible with the help of fluorescent liquid. The aim of the development work is to direct the water in such a way that the relevant fields of vision ideally remain clean. For this purpose, the aerodynamicists optimised, among other things, the contour of the A-pillars with integrated components as well as the shape of the exterior mirrors and window frames or the trim strips on frameless doors.

For example, minor geometric changes to the mirror housing and detailed optimisations with seals and a special water deflector strip can significantly reduce contamination on the side window. Mercedes Benz has the requirement that there must be no impairment of visibility due to spray, rivulets, or individual drops in the so-called core viewing area of the side window and on the exterior mirror glass.

In convertibles and roadsters, the aerodynamicists at Mercedes-Benz pay particular attention to what is known as draft-free comfort, i.e., an interior that is as wind-free and pleasantly tempered as possible. For example, the CLE Cabriolet comes standard with AIRSCARF® neck-level heating and the AIRCAP® electric wind deflector system. Both systems make open-top driving pleasant even in cool outside temperatures. The AIRSCARF® surrounds the neck and throat of the front occupants with pleasant warmth even in unfavourable wind conditions.

AIRCAP® can be extended at the touch of a button and then significantly reduces air turbulence in the interior of the four-seater. The system consists of two components: a wind deflector that can be extended by several centimetres with a net in the roof frame and a wind deflector that can also be extended behind the two rear seat headrests.

When extended, however, AIRCAP® is a potential source of noise. In the wind tunnel, the aerodynamicists therefore spent a long time fine-tuning the design of the system and its surroundings, thus reducing the noise to a minimum. The experts optimised, among other things, the choice of mesh fabric, the geometry of the fin, and other radii and shapes. The way the mesh fabric is flowed through and how both AIRCAP® components interact was also investigated and adapted to customer needs.