Abstract: The streamlined nose length (SNL) plays a crucial role in determining the aerodynamic performance of high-speed trains. An appropriate SNL can not only effectively reduce the magnitude of aerodynamic drag and lift forces, but also improve the performance of the high-speed train in tunnel passing and crosswind circumstances. In this study, a numerical simulation of the aerodynamic performance of high-speed trains at a speed of 400 km/h, with varying SNLs, is conducted using thek-ω shear stress transport (SST) turbulence model. The different SNLs include 6.0, 7.0, 8.0, 9.0, 9.8, 12.0, 15.0, and 18.0 m. In order to validate the accuracy of the numerical simulation, its results are compared with wind tunnel test data obtained from the literature. Numerical simulation is carried out using compressible and incompressible gases to determine the effect of gas compressibility on results. The impact of SNL on the aerodynamic performance of the trains is analyzed in terms of aerodynamic forces, velocity, and pressure distributions. In comparison to the original train, the train with a 6.0 m SNL experienced a 10.8% increase in overall aerodynamic resistance. Additionally, the lift forces on the head and tail cars increased by 35.7% and 75.5%, respectively. On the other hand, the train with an 18.0 m SNL exhibited a 16.5% decrease in aerodynamic drag. Furthermore, the lift forces on the head and tail cars decreased by 21.9% and 49.7%, respectively. The aerodynamic drag force of the entire train varies linearly with the SNL, while the aerodynamic lift of the tail car follows a quadratic function in relation to the SNL.

Key words: Streamlined nose length (SNL); High-speed train; Aerodynamic performance; Numerical simulation; Flow structures

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