Aerodynamics and aeroacoustics: Not a lot of turbulence

Jun 24, 2019
Stuttgart/Salt Lake City

The currently lowest aerodynamic drag of any SUV in its segment, and even less wind noise than in the preceding model – that was the development goal for the new GLS. This was achieved with Cd figures from 0.32 – a significant improvement over the preceding model (Cd = 0.35) and a benchmark among comparable full-size SUVs. The good aerodynamic properties make a key contribution to low fuel consumption under everyday conditions. A host of details was optimised with numerous computation loops, CAE simulations (computer-aided engineering) and measurements in the wind tunnel in Sindelfingen.

Major measures include, depending on the market, an active cooling-air control system behind the radiator grille for needs-based metering of the airflow (AIRPANEL) so that only as much air as absolutely necessary flows through and as much as possible flows around the vehicle. To ensure that it meets little resistance, wheel spoilers with aerodynamically shaped deflectors ahead of the front wheels were developed, with additional wheel spoilers ahead of the rear wheels. The side mirrors were optimised, as the turbulence they create not only generates drag, but also noises that are very close to the driver's ear. Acting together with the airflow around the A-pillars, this airflow substantially ensures that the side windows remain clean even when driving in the rain. The roof spoiler and the side spoilers, which are sealed against the D-pillar on the tailgate, as well as rear lights with special spoiler lips, ensure reduced turbulence at the rear end.

The large ground clearance of SUVs makes detailed improvements to the underbody particularly beneficial to the aerodynamics. The new GLS uses extensive panelling on the underbody and prop shaft tunnel for this purpose. Flush fuel tank panelling, an aerodynamic fairing at the rear axle and an aerodynamically optimised diffuser shroud reduce drag and noisy turbulence at the underbody. This is where particularly low-frequency wind noise otherwise arise. The wheels, a constant thorn in the side of the aerodynamics engineers, have also been optimised.

With regard to the large panoramic sliding sunroof, the aerodynamics specialists succeeded in achieving a level of noise comfort corresponding to that of a much smaller sliding sunroof by using numerous air deflection measures, specially shaped seals and covers. Indeed, a special programme was developed for the panoramic sliding sunroof to adapt the tilted position of the roof to the vehicle speed. As a result, the wind noise always remains pleasant without becoming intrusive.

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