Numerical Simulation of Leakage Effects on Sunroof Buffeting of an Idealized Generic Vehicle

Sunroof buffeting is a flow-acoustic resonance phenomenon that causes high interior noise leading to discomfort for the passengers. In order to make a priori predictions about the tendency of a given vehicle to experience buffeting with a high degree of reliability, it is important to understand the sensitivity of this phenomenon to various noise parameters. The current investigation studies the mechanism and the effect of leakage on an SAE Type 4 body. For this, the CAA tool PowerFLOW was used and good agreement of the peak SPL over a wide range of velocities between experiment and simulation was observed for the baseline configurations and the leakage configurations. This allows the analysis and identification of the mechanism for how the artificial leakage affects the buffeting behavior. I. Introduction UNROOF and side-window buffeting in passenger vehicles results in high sound-pressure levels in the interior and can cause considerable discomfort for the passengers. It is well understood that this phenomenon is a result of an unsteady shear layer in the sunroof or window opening which induces an acoustic resonance in the passenger compartment. Pragmatic design solutions for suppressing sunroof buffeting at various wind speeds and geometric configurations are well-known. However, a complete solution to this problem without resorting to expensive design measures has not been achieved in the industry. Recent numerical investigations 9,10 on real cars exhibiting real world effects have successfully predicted the effect of a deflector on buffeting suppression in an SUV. In a validation study 9 , the efficiency of a deflector system was studied on a sedan and an SUV. It was shown conclusively that a sunroof system which works well to mitigate buffeting on one vehicle cannot be assumed to be universally effective. Ref. 16 provided a detailed review of previous experimental and numerical investigations of this problem and concluded that many open questions remained in previous experimental and numerical studies and attempted a systematic investigation of the phenomenon of buffeting in automotive applications. Experiments were carried out on an SAE Type 4 body, a geometrically simple and structurally rigid vehicle model. This removed experimental uncertainties associated with geometric details and structural and acoustic properties of real vehicles. Two different wind tunnels were used to measure the acoustic response of the body at various wind speeds, in order to address wind tunnel affects. Ref. 15 which covered only the experimental portion of the study also investigated the effect of leakage on the overall buffeting behavior at various wind speeds. The leakage was represented by a round hole of 200 mm in diameter in the rear wall of the SAE Body. This study validates the buffeting behavior of the leakage configuration using numerical predictions over the relevant range of velocities.