Noise source identification of flow-induced inside-noise of motorcycle helmets

Abstract

Interior noise reduction is an important issue for motorcycle helmet quality. In this study, the relationship between the flow field outside the helmet and the internal noise was investigated for wind noise, and the aerodynamic sources that causes the internal noise were explored. Numerical simulation confirmed that the formation of vortices around the helmet. The acoustic field was generated at the point where the vortex convection caused by the detachment and reattachment of the flow, suggesting that the pressure fluctuation caused by the vortex formation contributed to the sound generation. Based on these numerical results, was experimentally measured using the coherent output power. As a result, strong correlations were confirmed among the shield, neck, and forehead/occipital projection areas. In particular, the shield and neck areas significantly contributed to the internal sound. The shield part is a stagnation point and the pressure fluctuation was small, suggesting the possibility of self-excited vibration with the hinge of the shield, while the neck part is thought to transmit internal sound due to pressure fluctuation caused by detachment and reattachment of the flow.