Study on the influence of the nose slenderness ratio of high-speed train on the aerodynamic noise

In the high-speed train design, the nose shape is a crucial control factor influencing not only aerodynamic performance but also the aerodynamic noise. In the engineering practice, the nose shape becomes more and more slender along with the increasing of the design speed, e.g. the Japanese high-speed maglev train L0 series even has a 15m long slender nose (the slenderness ratio reach to 8.8). This study aims to discuss the influence of the slenderness ratio of the nose shape on the aerodynamic noise. The hybrid numerical method of nonlinear acoustics solver (NLAS) and Ffowcs Williams-Hawkings (FW-H) acoustic analogy method is employed to study the aerodynamics noise characteristics. The numerical method is validated with a standard wind mirror test case and a set of acoustics wind tunnel experiments of the CRH380A train. The shape of the CRH380A train is chosen as a bench mark, and four different nose shapes of different slenderness ratio under different running speed situation are studied with numerical simulation. The flow field, aerodynamic drag, and the aerodynamic noise are obtained and discussed. The result shows that the total drag decrease with the increase of the slenderness ratio, and this effect enhances when the train speed increases. However, the influence of the slenderness ratio on the aerodynamic noise is much complex as no simple trend is observed. Considering both the aerodynamic and aeroacoustics characteristics, the train with the most slender nose shape is the best while this advantage is not notable compared with the second-best. Thus, simply increase the slenderness does not necessarily result in better aerodynamic noise performance if the effect of tunnel boom is not considered.