The effects of windscreen flow on noise in motorcycle helmets

Vortex shedding from a motorcycle windscreen results in three flow regions in which the rider's helmet may be immersed. First, the helmet may be completely in the free stream. Second, it may be in the path of vortex shedding from the windscreen. Third it may be underneath the shed vortices and shielded from the free stream by the windscreen. On-track noise tests were conducted and showed a difference in sound pressure level of more than 10dB and a change in spectra content, due to changes in riding position and helmet angle. Similar tests carried out in a wind tunnel, using simultaneous microphone and flow visualization measurements, allowed the identification of the flow regions. The potential contribution of vortex shedding to the noise was assessed using wavelet analysis to identify intermittent flow structures.