Experimental and Numerical Investigation of Automotive Wind Throb Phenomenon

Sunroof wind throb can generate annoyingly high sound-pressure levels (SPL) inside the vehicle cabin. In this study, several deflector configurations were installed to investigate this flow-acoustic coupled resonance phenomenon in passenger cars. In each condition, comparisons between the experimental results and numerical simulations were performed over a range of wind speeds to validate the capability of the PowerFLOW numerical simulation for wind throb prediction. Experiments were performed at the Suzuki full scale wind tunnel. One microphone in the cabin was set to record the pressure history and SPL. Flow around the sunroof was also measured by PIV. In both experiments and simulations, the following phenomena were observed. In case of strong wind throb, flow separates from the deflector and strong periodic vortices in the shear layer were observed. These vortices break down due to the impingement at the back-end of the sunroof and generate a strong peak noise in the cabin. In case of no wind throb, the periodic vortices were not observed resulting in a very weak peak with low SPL in the cabin. The deflector study shows that wind throb is a highly sensitive phenomenon where even a small geometry variation at the critical region can affect the phenomenon significantly. In this study, the same trend was obtained in the experimental results and simulations. It shows that the numerical simulation can be used for a priori predictions in the early stages of the vehicle design process.