Key Takeaways & Executive Findings
- •• Increasing train height from 3.89 m to 4.19 m raises the side force coefficient by up to 61.54% under a 20 m/s crosswind. • Roll moment coefficients on head, middle, and tail cars increase by 18.11%, 24.78%, and 34.23%, respectively, for the tallest train. • Taller trains intensify wake vortices and expand the back-flow region, increasing turbulent fluctuations and Reynolds stress on the leeward side. • The findings provide critical design references for optimizing train height to ensure stability and safety in crosswind conditions.
Abstract
The influence of train height on aerodynamic characteristics of high-speed train (HST) is significant in crosswind environments. This study employed the improved delayed detached eddy simulation (IDDES) turbulence model to analyze the aerodynamic characteristics of trains with three different heights under a crosswind of 20 m/s. The numerical model was validated through comparison with wind tunnel experimental data. A comprehensive analysis was conducted on the characteristics of the flow field around trains, surface pressure distribution, and aerodynamic loads for trains with different heights. Results indicate that the side force coefficient increased by up to 61.54% with an increase in train height from 3.89 to 4.19 m. Compared with the 3.89 m case, the roll moment coefficient on the head, middle, and tail cars for 4.19 m cases increased by 18.11%, 24.78% and 34.23%, respectively. The increase in train height widens the impact width of the leading car’s front vortex on the leeward side and intensifies the helical shedding and coupling interactions of two vortices in the wake, leading to an increase in the intensity and extent of wake flow in both vertical and longitudinal directions. Additionally, the increase in height shifted the flow separation point on the leeward side, moving vortices farther from the train, expanding the back-flow region, and intensifying Reynolds stress and turbulent fluctuations on the leeward side, which adversely impacted train stability and safety. The research findings can provide a reference for the design of train configurations and the assessment of dynamic performance in crosswind environments.
1. Introduction
The development of high-speed rail has greatly enhanced transportation efficiency between cities, reducing travel time and stimulating economic growth. However, the available capacity of some railway lines has proven insufficient to meet the growing demand for passenger services in recent years [1, 2]. Double-deck high-speed trains (DDTs) accommodate the growing demand for passenger travel by arranging double-deck seats, alleviating congestion on some high-demand routes. Compared with conventional single-deck electric multiple units (EMUs), DDTs can increase passenger capacity by approximately 30% to 50% [3], bringing significant economic and social benefits. Due to their high efficiency in terms of mass-based transport capacity and low energy consumption per passenger, DDTs have gained widespread attention. Countries like Japan and France have introduced various DDTs to meet the growing demand, including Japan’s E4 series, and France’s TGV Duplex, TGV Dasye, and Euroduplex.
However, DDTs also pose aerodynamic performance challenges with increasing train height. Lower-centered trains can exhibit lower drag and superior dynamic performance [4]. The unique shape of DDTs results in a higher center of gravity, leading to inferior dynamic performance compared to single-deck high-speed trains. Additionally, the aerodynamic characteristics of the train are significantly influenced by its geometry. Train heights alter the train’s cross-sectional aspect ratio and tail slant angle, which will directly influence train aerodynamic performance. For example, WANG et al [5] analyzed how train height affected the surrounding aerodynamic performance when running on an open line. The findings reveal that both lift and overall drag increase with train height. The wake flow develops outward and downward as height increases because it speeds up the mixing of downwash with ground flow. Moreover, the boundary layer height near the train significantly rises as train height increases, posing potential risks to nearby facilities and people.
The flow field around a train becomes highly complex under crosswind disturbances, making its aerodynamic performance more sensitive to variations in geometric characteristics [6]. Researchers have discovered factors impacting the train’s aer... (text truncated)
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XIONG Xiao-hui, LIU Li-ying, CHEN Guang, CHEN Bo, XUE Ru-dai, WANG Kai-wen (2025). Effect of train heights on aerodynamic performance of high-speed trains under crosswind. Journal of Central South University. https://doi.org/10.1007/s11771-025-6049-5
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Frequently Asked Questions
What is the main objective of this study?
The study investigates the effect of train height on the aerodynamic performance of high-speed trains under crosswind conditions, using numerical simulations validated with wind tunnel data.
How does increasing train height affect aerodynamic loads?
Increasing train height from 3.89 m to 4.19 m increases the side force coefficient by up to 61.54% and roll moment coefficients on head, middle, and tail cars by 18.11%, 24.78%, and 34.23%, respectively.
What turbulence model was used in the simulations?
The improved delayed detached eddy simulation (IDDES) turbulence model was employed to analyze the aerodynamic characteristics.
What are the practical implications of this research?
The findings provide a reference for designing train configurations and assessing dynamic performance in crosswind environments, particularly for double-deck high-speed trains.
How does train height influence the wake flow?
Taller trains intensify wake vortices, expand the back-flow region, and increase turbulent fluctuations and Reynolds stress on the leeward side, which can adversely affect stability and safety.
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