The effects of windscreen flow on noise in motorcycle helmets.

Abstract

Vortex shedding from a motorcycle windscreen results in three flow regions into which the helmet of the rider may be immersed. First, the helmet may be fully in the free stream. Second, the helmet may be directly in the path of vortex shedding from the windscreen. Third, the helmet may be beneath the vortex shedding and shielded from the free stream by the windscreen. On-track tests were conducted and show a difference in sound pressure level of over 10 dB and a change in spectral content for different riding positions and helmet angle. Similar tests were then conducted in a wind tunnel, where simultaneous microphone and flow visualisation measurements allowed the identification and investigation of each flow region under controlled conditions. The contribution of vortex shedding to the noise was assessed using a combination of wavelet analysis and conditional averaging to identify intermittent structures.