Numerical Analysis of Aerodynamic Noise Emitted from a Pantograph Based on Non-compact Greens Function

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In this study, mathematical formulae for evaluating scattered components of non-compact sound are summarized, and aerodynamic noise emitted from a pantograph is predicted numerically based on the theory of vortex sound. When influence of reflection at the plane (train roof) is taken into consideration in Greens functions, interference of sound waves appears and amplitude of sound pressure at an observer located in a far field is strengthened and weakened periodically depending upon its frequency, which phenomenon is similar to the experimental results. In the low frequency range, large separations occurring at the upper and lower sides of a pantograph head, lower sides of the pantograph head support, and an upper frame are main sources of scattered sound propagating upward. In the high frequency range, sound seems to be generated by unsteady motion of small vortices shed from the pantograph head and the support. As for sound propagating sideward, release of large-scale vortices from the support and the upper frame in horizontal planes is responsible for low frequency noise, and longitudinal vortices rolling up along sides of the support seem to generate sound of high frequency.