by Adrian-Liviu Dorofte

The new Mercedes-Benz A-Class: Aerodynamics - Saving fuel the aerodynamic way

With a drag coefficient (Cd) value of 0.27, the aerodynamic experts at Mercedes-Benz succeeded in creating another masterpiece with the A-Class. And the A 180 BlueEFFICIENCY Edition due to follow later is even able to exceed this record for hatchback vehicles: thanks to a number of aerodynamic enhancements, this beacon of efficiency achieves a Cd value of 0.26.

Countless flow simulation studies on the computer and a great deal of fine tuning in the wind tunnel resulted in a clear goal: to enhance the basic shape of the A-Class design further, with a view to achieving an exceptional drag coefficient. This is no easy task, particularly for a hatchback model with a short rear overhang. But an improvement in the Cd value of just one hundredth will reduce fuel consumption by one tenth of a litre per 100 km when driving on the motorway at approx. 120 km/h. Based on NEDC figures, this corresponds to a CO2 reduction of one gram per kilometre. With a Cd value of 0.27 and a frontal area of 2.20 m2, the drag area (CdA) is less than 0.6 m2 – a benchmark figure for hatchback vehicles in this segment.

The detailed work behind this development is highlighted by the following examples:

- The distinctive side spoilers next to the rear window ("finlets") help to create a run-on design which significantly reduces the disruptive longitudinal vortices generated at the D-pillars.

- Flow losses at the front wheel arches have been reduced substantially with the aid of patented serrated wheel spoilers at front and rear, slots in the wheel arches and optimised hub caps. These measures result in improved wind flow around the wheel arches.

- The A-Class has an adjustable radiator shutter, already familiar in larger model series. The louvres behind the radiator grille are for the most part closed when there is no specific need for cooling air.

- The underbody has also been aerodynamically enhanced: 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 new A-Class features exterior mirrors which have been optimised in terms of a number of details and already proven their excellent aerodynamic properties in large model series such as the S, E and C-Class, and also the B-Class. The position of the exterior mirror is adjusted in respect of the A-pillar in such a way that the airflow is directed along the side window without any significant interference or disruption.

The exterior mirrors and the low stepped height of the A-pillars reflect the fact that the work conducted in the wind tunnel was not just about optimising the flow conditions, but also about minimising wind noise. And in addition to aerodynamics and aeroacoustics, there is often another discipline to consider: in terms of water management too, the flow around the exterior mirrors and the A-pillars also has to be optimised in the wind tunnel in order to guarantee good visibility is maintained towards the rear and at the sides during wet weather.

More than with previous model series, in the case of the A-Class the aerodynamics experts at Mercedes-Benz made particular use of flow simulation (CFD, Computational Fluid Dynamics): each component was first improved over several cycles using flow simulation before having its aerodynamic properties put to the test in the wind tunnel.

Digital flow simulation is based on so-called finite volumes as a mathematical model. A volume net is formed from around 60 million hexahedrons, or cubes, and is based around the CAD data of the new A-Class. This enables the driving cycle to be simulated over a free area in a large virtual wind tunnel. The Mercedes engineers generate the airflow using a predetermined turbulence level.

Setting new standards in terms of Cd value and consumption: BlueEFFICIENCY Edition
Due to follow later is the A 180 CDI BlueEFFICIENCY Edition boasting even better consumption levels. It is among the most efficient vehicles of its class: thanks to a series of additional aerodynamic optimisation measures, it has been possible to reduce its Cd value from 0.27 (standard model) to 0.26.

These measures include:

- partially covering the upper part of the radiator grille

- aerodynamically shaped spring link coverings to improve the underbody airflow at the rear axle

- lowering of the suspension by 15 mm

Credits: Daimler AG

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