Key Takeaways & Executive Findings
- •• Temperature and scale ratio significantly influence the timing of shock wave generation during acceleration, altering aerodynamic drag. • At constant speed, these parameters affect the onset of choked flow and its length, impacting drag. • During braking, variations in temperature and scale ratio change the timing of shock wave disappearance and expansion wave reflections, affecting drag reduction. • The study provides insights for optimizing vacuum tube maglev system design and safety by controlling environmental and geometric parameters.
Abstract
The airflow around a vacuum tube maglev train operating at high speeds is complex. In addition, the effect of relevant parameters in such a transportation system on aerodynamic characteristics is crucial in the design and safety of the system. A three-dimensional (3D) vacuum tube train model is established based on a vacuum tube test platform for rail transit. The effects of the initial ambient temperature and scale ratio on the aerodynamic characteristics are analyzed during the whole operational process in this study. The results mainly focus on each process's variations in the shock waves, choked flow, and drag. During acceleration, shock wave generation is advanced or delayed under different system parameters, which vary the aerodynamic drag. While the train runs at a constant speed, the time that a standard shock is generated and the length of the choked flow differ under the effects of the varying system parameters. In braking, the disappearance of shock waves and reflections of the expansion wave suddenly decrease the aerodynamic drag either earlier or later due to the varying system parameters.
1. Introduction
Maglev trains benefit from high speed and the elimination of friction caused by wheels and rail [1]. However, aerodynamic characteristics at increased traveling speed significantly affect traditional wheel and maglev trains. Fortunately, vacuum tube transportation can effectively reduce aerodynamic drag and substantially improve speed by combining the technologies of magnetic levitation and vacuum [2]. Several countries, such as China [3], South Korea [4], and America [5], continually study vacuum tube trains. However, the operation of vacuum tube transportation faces many inevitable problems. With increasing speeds, the generation of choked flow [6, 7] and shock waves [8, 9] causes complex aerodynamic phenomena that drastically affect the internal operating environment of the tube and the train’s safety [10]. Therefore, research on aerodynamic characteristics is crucial to designing vacuum trains and achieving this concept [11].
Numerical simulations are utilized primarily for aerodynamics research, with the advantages of low cost and easy process realization in the vacuum tube transportation field [12, 13]. Numerous numerical simulations from previous studies have summarized that the blocking ratio, vacuum degree, and initial ambient temperature are important factors [14−18]. Among these factors, the blocking ratio has the most significant effect on the aerodynamic drag, which has a linear relationship with the vacuum degree [19 −21]. In addition, relevant studies have illustrated that an increased initial ambient temperature decreases aerodynamic drag [22]. Furthermore, the generation of shock waves controlled by the threshold values of the blocking ratio and speed dramatically improves the aerodynamic drag [23]. The generation of choked flow significantly increases the aerodynamic drag [24, 25].
Several studies have described the effects of shock waves and choked flow on aerodynamic drag from the perspective of aerodynamic phenomena. ZHOU et al [26] analyzed different kinds of shock wave structures. Subsequently, the generation, development, and disappearance of various shock waves were comprehensively described. BAO et al [27] proposed that an increased ambient temperature significantly decreases the intensity of the shock wave while the structure of the shock wave shortens. ZHOU et al [28] demonstrated that an increased blocking ratio helps delay boundary layer separation, as shock waves are fully developed, based on simplified two-dimensional (2D) evacuated tube train simulations.
In practice, train movement in vacuum tubes is a complete process that combines acceleration, uniform motion, and deceleration. BI et al [29] studied the aerodynamic characteristics of vacuum tube trains and analyzed variations in shock waves, choked flow, and aerodynamic drag during each process. NIU et al [30] presented the effects of acceleration and deceleration on the aerodynamic characteristics. However, these works simplified the actual operational processes and ignored the influence of other environmental factors.
The above studies comprehensively considered the aerodynamic characteristics of the train operating in a vacuum tube. However, they did not consider the effects of the blocking ratio and other initial environmental conditions.
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BI Yun-feng, BI Hai-quan, WANG Hong-lin, ZHOU Yuan-long, YANG Ji-zhong, JIANG Yao, ZHANG Nan (2025). Numerical study on the effect of temperature and scale ratio on aerodynamics of maglev trains moving dynamically in a vacuum transportation system. Journal of Central South University. https://doi.org/10.1007/s11771-025-6063-7
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Frequently Asked Questions
What is the main objective of this study?
The study numerically investigates the effects of initial ambient temperature and scale ratio on the aerodynamic characteristics of a maglev train moving dynamically in a vacuum tube, focusing on shock waves, choked flow, and drag during acceleration, constant speed, and braking.
How does temperature affect the aerodynamics of vacuum tube maglev trains?
Increased initial ambient temperature generally decreases aerodynamic drag and can alter the timing of shock wave generation and disappearance, as well as the length of choked flow, thereby influencing the overall aerodynamic performance.
What is the role of scale ratio in vacuum tube train aerodynamics?
The scale ratio (related to blocking ratio) significantly affects aerodynamic drag and the development of shock waves and choked flow. Different scale ratios can advance or delay shock wave generation and change the duration of choked flow, impacting drag.
What are the practical implications of this research?
The findings provide insights for optimizing the design and operation of vacuum tube maglev systems, such as selecting appropriate ambient temperatures and scale ratios to minimize aerodynamic drag and enhance safety.
What methods were used in this study?
A three-dimensional (3D) vacuum tube train model was established based on a vacuum tube test platform, and numerical simulations were performed to analyze the aerodynamic characteristics under varying temperature and scale ratio conditions.
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