Aeroacoustic tests were performed on three motorcycle helmets to determine how the gaps, seals, and edges of a helmet affected the wind noise generated by the helmet. To simulate the conditions a helmet would encounter when worn by a motorcyclist, the helmets were placed on the head of a mannequin, which was then placed in the uniform flow of a wind tunnel. A microphone, located inside the right ear of the mannequin, picked up the wind noise transmitted into the helmet. A sound level meter, attached to the microphone, measured the overall and octave band decibel levels of the noise reaching the microphone. These sound levels represented the noise levels that would be heard by a motorcyclist travelling at cruising speeds of about 100 km/h (60 MPH). The gaps, edges, and general shapes of the three helmets were modified and each helmet modification was tested to determine how it had changed the air flow around the helmet and the amount of wind noise at the ear. At typical cruising speeds, around 100 km/h, a standard, unmodified, helmet generated noise levels that would be a long term hazard to the motorcycle rider's hearing, and would mask warning signals from other road traffic. It was found that these excessive wind noise levels could be significantly reduced by making relatively simple changes to the design of the helmet. In other tests the effect of a turbulent shear layer impinging on the helmet, as from a fairing, was found to increase the sound level further above that with a uniform flow.
Samenvatting