Glass Transmission Mechanism of Flow-Induced Noise from the Forward Facing Step

Abstract

In recent years, the engine noise level has been reduced due to powerplant electrification seen in EVs and HEVs for improving fuel economy. At the same time, the wind noise has become more noticeable to the degree that may take away driver comfort. At Honda, we have verified that the contribution of wind noise increases as the speed of EV increases. Among different wind noise types, the high frequency aeroacoustic noise (1k-5kHz) is generated by the flow around the side mirrors and front pillars, and it is transmitted into the cabin through the side window glasses. However, the mechanism of noise generation and transmission has not been fully understood. In this research, our focus is to clarify control object for the reduction of the high frequency aeroacoustic noise into the cabin. We use a simplified noise transmission model in which the noise from a forward facing step mocking car pillar being transmitted into a box set as car cabin. By applying CFD and CAA analysis validated by wind tunnel experiments, we identify the contribution of convectional pressure fluctuations and/or acoustic sounds. Our analysis results show that the prediction values of the box sound pressure which takes account of convectional pressure fluctuations and acoustic sounds have a good agreement with the experiments, and the contribution of acoustic sounds is about 93% of the sound pressure in the box. Finally, we clarify that in case of high frequency aeroacoustic noise, the acoustic sounds induced by the flow around the forward facing step are directly transmitted into the box.