An Experimental Study of the Vertical Directivity Pattern of Wheel/Rail Rolling Noise

An experimental approach for studying the vertical directivity pattern of noise radiated from a passing train is presented. Four sets of noise measurements are conducted at three different sites, including ballast tracks at grade and railway on a concrete viaduct. The time histories computed from a horizontal radiation model are compared with the measured noise profiles. The measured sound exposure levels are used to deduce the vertical directivity pattern for different railway systems of continuously welded rail systems. It is found that the vertical directivity of different railway systems shows a rather similar pattern. The vertical directivity of train noise is shown to increase up to about 30° before reducing to a minimum at 90°. A multipole expansion model is proposed to account for the vertical radiation directivity of the train noise. The empirical model is found to be applicable to different train/rail systems at train speeds ranging up to 120 km/h.