Key Takeaways & Executive Findings
- •• Higher blockage ratios intensify shock waves in evacuated tubes, while larger tunnel areas mitigate this effect, improving flow structure and wake behavior. • Reducing the blockage ratio from 0.253 to 0.121 decreases the total drag coefficient of the entire train by 46.2%, with head and tail carriage drag coefficients dropping by 23.3% and 32.7%, respectively. • The drag contribution shifts from the head carriage (decreasing from 51.1% to 40.9%) to the tail carriage (increasing from 47.0% to 56.6%) as blockage ratio decreases. • The study provides critical insights for optimizing evacuated tube transportation design to enhance aerodynamic performance and energy efficiency.
Abstract
Evacuated tube transportation (ETT) offers a promising high-speed transport solution, but trains operating at supersonic speeds within a sealed tube can induce complex aerodynamic phenomena that impact safety and reliability. This study utilized the Reynolds-averaged Navier-Stokes (RANS) shear stress transport k-ω (SST k-ω) turbulence model for steady-state simulations and the improved delayed detached eddy simulation (IDDES) SST k-ω model for unsteady-state simulations, both coupled with the advection upstream splitting method (AUSM). Four tunnel cross-sectional areas (49 m2, 64 m2, 81 m2, and 100 m2) with corresponding blockage ratios (β) (0.253, 0.192, 0.150, 0.121) were analyzed to explore shock wave formation and its dependence on blockage ratios, along with surface pressure distribution and aerodynamic loading. Results show that higher blockage ratios increase shock wave intensity, while larger tunnel areas reduce this intensity, improving flow structure and wake effects. Moreover, as the blockage ratio decreases, the total drag coefficient of the entire train decreases linearly. When the blockage ratio decreases from 0.253 to 0.121, the total drag coefficient of the entire train decreases by 46.2%, with the head carriage and tail carriage drag coefficients decreasing by 23.3% and 32.7%, respectively, while the drag coefficient of the middle carriage remains nearly unchanged. The percentage of the total drag coefficient contributed by the head carriage decreases from 51.1% to 40.9%, while the percentage for the tail carriage increases from 47.0% to 56.6%. These findings enhance understanding of ETT fluid dynamics and performance.
1. Introduction
Rail transportation plays a pivotal role in the development of urban systems by efficiently transporting large volumes of passengers and goods, thereby supporting environmental protection and sustainable growth. However, conventional rail systems face limitations, such as slower speeds and the rigidity of fixed routes, which restrict transportation flexibility. As rail systems evolve, increasing train speeds represents a key breakthrough. To address the efficiency challenges of traditional trains, evacuated tube transportation (ETT) has emerged as a promising solution.
ETT is an environmentally friendly, energy-efficient mode of transportation that is gaining global attention. As an advanced transportation system, evacuated tube trains are a focal point in the future development of rail transit. Countries such as the United States, Switzerland, Japan, and China are making significant investments in scientific research to advance the next generation of maglev trains. Aerodynamic drag increases quadratically with train speed in open-air environments, and at speeds exceeding 300 km/h, aerodynamic drag can contribute more than 80% of total drag. Additionally, the fluctuating pressure caused by high-speed trains passing through open air or tunnels can damage the train structure and cause discomfort for passengers. ETT, by contrast, offers reduced aerodynamic friction. In this system, a vacuum is maintained in a sealed tube, and, unlike conventional trains exposed to factors like crosswinds, rain, and snow, the enclosed ETT environment ensures greater safety and passenger comfort. With significantly lower drag, the resistance in ETT systems is drastically reduced, leading to lower energy consumption and reduced aerodynamic noise, thus meeting environmental protection standards. Therefore, the development of energy-efficient, environmentally friendly, and high-speed rail technology is centered on ETT.
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HUANG Zun-di, PENG Cheng, CHEN Zheng-wei, GUO Zi-jian, CHANG Ning, KONG Wei-kai, GUO Zhan-hao, LU Jia-hao (2025). Shock wave behavior and aerodynamic load in maglev-equipped evacuated tubes: Effects of blockage ratio. Journal of Central South University. https://doi.org/10.1007/s11771-025-6150-9
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Frequently Asked Questions
What is the effect of blockage ratio on shock wave intensity in evacuated tubes?
Higher blockage ratios increase shock wave intensity, while larger tunnel areas (lower blockage ratios) reduce this intensity, improving flow structure and wake effects.
How does the blockage ratio affect the total drag coefficient of the train?
As the blockage ratio decreases, the total drag coefficient decreases linearly. Reducing the blockage ratio from 0.253 to 0.121 results in a 46.2% decrease in total drag coefficient.
What are the specific drag coefficient changes for different carriages when blockage ratio is reduced?
The head carriage drag coefficient decreases by 23.3%, the tail carriage by 32.7%, while the middle carriage remains nearly unchanged. The head carriage's contribution drops from 51.1% to 40.9%, and the tail carriage's contribution rises from 47.0% to 56.6%.
Which turbulence models were used in this study?
The study used the Reynolds-averaged Navier-Stokes (RANS) shear stress transport k-ω (SST k-ω) model for steady-state simulations and the improved delayed detached eddy simulation (IDDES) SST k-ω model for unsteady-state simulations, both coupled with the advection upstream splitting method (AUSM).
What is the significance of this research for evacuated tube transportation?
The findings enhance understanding of ETT fluid dynamics and performance, providing insights for optimizing tunnel cross-sections and train designs to reduce aerodynamic drag and improve safety and energy efficiency.
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