Evaluation of noise reduction strategy using porous rings by acoustic analysis and wind tunnel experiments

High-speed trains operating in Japan are equipped with pantographs, which are devices that collect the electricity necessary for running. Lately, as high-speed trains have become faster, the increase in aerodynamic noise caused by protruding objects such as pantographs has become a serious issue. It is known that aerodynamic noise increases in proportion to the sixth power of the flow velocity, and immediate measures are required not only to improve ride comfort and convenience, but also to reduce the environmental impact. However, there are many unknowns regarding the mechanism of aerodynamic noise generation, and effective reduction methods have not yet been established. In this study, as a basic experiment, the noise reduction effect of a cylindrical ring attached to an inclined cylinder simulating part of a pantograph was focused on, and changes in noise characteristics were evaluated based on ring shape parameters. Furthermore, it was shown that using porous materials for the ring material results in greater noise reduction effects. In addition, the flow around the cylinder and ring was visualized using numerical fluid analysis, and the sound pressure propagation characteristics were visualized using acoustic analysis. From the results obtained, the noise reduction mechanism achieved by using porous materials was clarified.