Aerodynamic noise from a high speed train pantograph and recess

Abstract

As high speeds bring higher levels of noise, noise reduction has become an important consideration for high-speed train design. In this study, the flow behaviour of a simplified geometry representing a high-speed train roof and cavity with pantographs at 1/10 scale is investigated. Computational Fluid Dynamics simulations are used based on the Improved Delayed Detached-Eddy simulation method to determine the near-field flow behaviours. The equivalent source terms are then used to predict the far-field acoustic pressure using the Ffowcs Williams-Hawkings acoustic analogy. The effect of the pantograph cavity is studied by comparing the flow behaviour and radiated noise from cases with two pantographs, one raised and one retracted, mounted either in a cavity or on a flat surface. In comparison with case with the flat surface, the flow around the pantographs with the cavity has slightly different characteristics. The cavity slightly reduces the flow velocity upstream of the raised pantograph, and changes the unsteady flow and its interactions with the pantographs, which leads to reduced surface pressure fluctuations and noise radiated from the raised pantograph. The trailing edge of the cavity also generates a highly unsteady flow. The highly unsteady flow over the cavity is significantly reduced by introducing modified leading and trailing cavity edges, which are rounded or angled. Consequently, noise radiated from the cavity is reduced compared to a rectangular cavity. Furthermore, the effect of rounded cavity edges on the flow over the pantographs is also investigated by comparing the flow features and noise contributions from the cases without rounded cavity edges. A slightly lower flow speed occurs around the upper parts of the raised pantograph, whereas the flow velocity in the cavity is slightly increased compared to the rectangular cavity. It is shown that, by rounding the cavity edges, a reduction in radiated noise can be obtained. The influence of three different roof configurations is also studied by comparing the flow behaviour, including flow separations, reattachment and vortex shedding, which are potential noise sources. A highly unsteady flow occurs downstream when the train roof has a cavity or ramped cavity due to flow separation at the cavity trailing edge, while vortical flow is generated by the side insulation plates. When the retracted pantograph is located inside the ramped cavity, its noise contribution is less important. Furthermore, the insulation plates also generate tonal components in the noise spectra. For the three configurations considered, the roof configuration with a conventional cavity radiates the least A-weighted noise at the side receiver.

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Identifiers

ORCID for Hogun Kim: orcid.org/0000-0001-6887-8483

ORCID for Zhiwei Hu: orcid.org/0000-0001-6737-4363

ORCID for David Thompson: orcid.org/0000-0002-7964-5906

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