Numerical Study of the Unsteady Aerodynamic Performance of Two Maglev Trains Passing Each Other in Open Air Using Different Turbulence Models  
[PERSON]  
1 Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering, Central South University, Changsha 410075, China; [EMAIL_ADDRESS]  
[PERSON]  
2  
[PERSON]  
1 Key Laboratory of Traffic Safety on Track of Ministry of Education, School of Traffic & Transportation Engineering, Central South University, Changsha 410075, China; [EMAIL_ADDRESS]  
Footnote 1: email: {[EMAIL_ADDRESS]}  
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The aforementioned studies mainly focused on the aerodynamic performance of two HSTs passing each other in open air. In recent years, maglev trains (MTs) have been recognised as safe, comfortable, low energy-consumption, and environmentally friendly ground vehicles [12; 13]. Germany, Japan, the UK, South Korea, and China have developed MT technologies. Similar to HSTs, MTs also have a large length-to-width ratio body. However, there are significant differences between HSTs and MTs, as shown in Figure 1. On the one hand, the operating boundary conditions near the ground are different as the HST wheels are in contact with the rail, and the space at the bottom of the train is open. Meanwhile, MTs levitate without contact with the ground, and the space at the bottom of the train is relatively confined. On the other hand, the geometry of the body surface is different as the HST contains bogies, cavities, pantographs, etc., whereas the external surface of MTs is smooth. These differences may cause the flow fields around these trains to be notably different. In addition, the MT speed is higher than the HST speed. For example, the Shanghai commercial maglev line reaches 430 km/h. The effect of time-varying lift forces on the HST is almost negligible as two trains pass each other because of the large mass [14]. However, the variation of the lift force during the passage of MTs can impair the levitation stability. This issue has motivated several investigations of the aerodynamic performance of two MTs when passing each other. [PERSON] et al. [1] used the unsteady RNG k-\(\epsilon\) turbulence model to investigate the transient pressure and slipstream velocity induced by two high-speed MTs meeting at a speed of 430 km/h in open air. [PERSON] [15] analysed the pressure pulse and aerodynamic force of two high-speed MTs passing each other using the SST k-\(\omega\) model and the overset mesh method. [PERSON] et al. [16] utilised the two k-\(\epsilon\) equation models to simulate the aerodynamic performance of two MTs passing each other and improved the aerodynamic performance of them by increasing the streamlined nose length and optimising the body shape. Although the aerodynamic performance, including the transient pressure and the aerodynamic force, of two MTs passing each other in open air has been well investigated, relatively few studies have been conducted on the evolution mechanisms and basic laws of the airflow around the train, especially the unsteady wake flows. Wake flows when a single train runs in open air have also been investigated [17; 18; 19]. The surrounding flow of two trains passing each other in open air is different from that of a single train moving in  
Figure 1: Photographs of a (**a**) maglev train and (**b**) high-speed train. open air. The present study aims to explore the flow around two MTs passing each other and to identify the vital flow mechanisms for their aerodynamic performance. To the best of our knowledge, few studies have considered the effect of the turbulence model on the aerodynamic performance of two meeting MTs.