Numerical Analysis of Aerodynamic Noise from a Pantograph Based on Non-Compact Green's Function

Abstract

In this study, mathematical formulae for evaluating scattered components of non-compact sound are summarized, and aerodynamic noise from a pantograph is predicted numerically based on the theory of vortex sound. When influence of reflection at the ground is taken into consideration in Green's functions, interference of sound waves appears and amplitude of sound pressure at an observer locating in a far field strengthens and weakens 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 produced 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 produce sound of high frequency.