Aerodynamics: Taking the drag out of aerodynamics

Oct 3, 2011
  • New benchmark for cars with station wagon rear end: cd = 0.26
An outstanding drag coefficient of cd = 0.26 places the new B-Class at the
forefront of its market segment. In practical driving, aerodynamics have a crucial influence on fuel consumption: an improvement in the cw value of just 0.01 results in fuel savings of up to 0.4 litres per 100 kilometres at a speed of 130 km/h.
"A whole range of measures were necessary in order to attain the excellent drag coefficient of cw = 0.26," explains Dr. Teddy Woll, Head of Aerodynamics at Daimler AG. "Apart from an aerodynamically efficient basic design, these include numerous optimisation measures on points of detail, such as the air flow around the front wheels, the underbody design and the flow of cooling air."
Designers and aerodynamicists worked closely together. Aerodynamically
efficient lines are demonstrated by the exterior mirrors with braces, for example. The low height of the shoulder on the A-pillar with optimised geometry also contributes to the good aerodynamics. The entire front apron is sealed, including special seals fitted on the headlamps, for example. The large roof spoiler at the rear provides for defined flow separation.
Flow losses at the front wheel arches have been reduced substantially with the aid of innovative serrated wheel spoilers at front and rear - patent pending -, slots in the wheel arches and optimised hub caps. These measures result in improved wind flow around the wheel arches.
Equally comprehensive measures have been undertaken to design the underbody along aerodynamic lines. The main floor panel features extensive cladding up to the rear wheel arch, followed by additional cladding of the rear axle. The rear silencer has also undergone aerodynamic optimisation.
The improved cooling air flow by means of an adjustable radiator shutter is familiar from other Mercedes models. This feature enables infinite adjustment of the air flow through the engine's cooling module and the engine compartment by means of a circular louvred shutter installed in parallel with the fan. When there is no special need for cooling air, the shutter is closed. This improves the aerodynamics and reduces fuel consumption.
The aerodynamics of the new B-Class were optimised at an early stage in the development process by means of complex computer calculations and flow simulations. Over 275,000 CPU hours were required for the purposes of digital flow simulation. Models and prototypes spent around 1100 hours in the wind tunnel for measurement purposes.