Experimental and Numerical Analysis of Sunroof Buffeting of a Simplified Mercedes-Benz S-Class 2021-01-1051

Sunroof buffeting is examined experimentally and numerically in this paper. Despite the fact that some consider the simulation process for sunroof buffeting to be mature, there remain substantial uncertainties even in recently published methodologies. Capturing the frequencies and especially the sound pressure levels correctly is essential if CFD simulations are intended to be used during early stages of a car development process. Numerous experimental results of sunroof buffeting and the interior low-frequency characteristics of a 2013 Mercedes-Benz S-Class have been used to develop a simplified car model: a full-size S-Class model with slightly simplified geometries in the interior as well as at the exterior. To avoid the effects of numerous different materials in the interior, it is solely made from polyurethane and aluminum and built to maximize its structural rigidity and air-tightness. The air-tightness of the cabin and structural modes of body parts have the greatest impact on the Helmholtz frequencies, which are excited by the vortex shedding in the sunroof opening.

With this simplified car model various measurements are carried out to validate the numerical simulation method. The measurement data consists of acoustic data as well as flow quantities. In this paper, Star-CCM+ is used to conduct improved delayed detached eddy simulations with direct noise calculation in order to predict the buffeting frequencies that occur at different wind speeds correctly. Due to the rigid and acoustically hard walls of the simplified car model, which fairly match the numerical boundary conditions, it is possible to predict the interior sound pressure levels correctly as well.

The presented results demonstrate that state-of-the-art CFD codes are capable of predicting sunroof buffeting frequencies and noise levels correctly if the experimental and numerical boundary conditions match.