Comparative study on the effect of aerodynamic braking plates mounted at the inter-carriage region of a high-speed train with pantograph and air-conditioning unit for enhanced braking
Introduction
Continuous improvements in the speed of high-speed trains have led to a significant increase in the kinetic energy of such trains, causing wheel rail adhesion to decrease gradually. Thus, a high-speed train with a disc brake and other adhesion braking mechanisms must undergo severe tests (Wei et al., 2016, 2017; Peng et al., 2017; Wu et al., 2019). Based on the successful application of aerodynamic braking in aircraft, as observed in Fig. 1, this mechanism has been applied to the braking system of trains. The adhesive braking force of a train begins to decrease when the train reaches the critical speed limit. Based on the linear relationship between the aerodynamic drag and quadratic power of speed (Schetz, 2001; Raghunathan et al., 2002; Tian, 2009; Baker, 2014), the greater the train speed, the better is the effect of the braking plate on increasing the effect of aerodynamic drag.
In terms of the engineering of the aerodynamic braking mechanism in high-speed trains, Japan is at the forefront. As shown in Fig. 2, before the opening of the Shinkansen railway in Hokkaido in 1955, some relevant research was conducted in Japan, various aerodynamic brake plates were developed, and full-scale online train tests and scaled model experiments were conducted (Sawada, 1996; Yoshimura et al., 2000; Shirakuni et al., 2002; Takami, 2013; Takami and Maekawa, 2017). In recent years, China has begun to study the aerodynamic braking technology of high-speed trains based on numerical simulations, scaled model experiments, and full-scale train tests (Wu et al., 2011; Jianyong et al., 2014; Niu et al., 2020a, 2020b). Tests and numerical simulations on trains have shown that the aerodynamic braking technology is an effective emergency-braking technology in high-speed trains, and its successful implementation has been achieved (Puharić et al., 2014; Gao et al., 2016). According to previous studies, most aerodynamic braking plates are usually installed on the top of trains. An inter-carriage region plays a vital role in increasing the aerodynamic drag of a train (Watkins et al., 1992; Ding et al., 2016; Niu et al., 2019; Li et al., 2019a), and is thus a good choice for installation of the plates. Therefore, different configurations of plates must be designed to determine the optimal design that could achieve the maximum drag; this is possible by converting the outer windshield into a brake plate.
In this study, analysis and comparisons were conducted on three configurations of aerodynamic braking plates installed at the car-connecting parts, as well as on the aerodynamic behaviour of the high-speed train installed with these plates. The main objective of this study is to introduce the mechanism of increasing aerodynamic drag of the train based on three plate configurations installed at the car-connecting parts of the train, and then evaluate the effect of these configurations on the increase in the aerodynamic drag and the surrounding flow field around the train. The study findings are conducive to helping engineers design and operate an aerodynamic braking system in high-speed trains.
The remainder of this paper is organised as follows. Section 2 presents some numerical simulations, such as those of train models, computational domain, and grid generation. Section 3 presents the numerical algorithm, grid resolution, and verification. In Section 4, we present the results and discussion including force analysis, braking distance calculation, and characteristics of the flow field. Finally, some key conclusions are listed in Section 5.
Section snippets
Geometric models
In this paper, three plate configurations are proposed, as presented in Fig. 3: C1 (opening the upstream part of the external windshields as braking plates), C2 (opening the downstream part of the external windshields as braking plates), and C3 (opening both parts of the external windshields as braking plates). The 3D view of the uniform vehicles with plates having configuration C1 is shown in Fig. 4(a). Considering that the uniform vehicle is the main component of a high-speed train, to reduce
Numerical algorithm
In this study, a Reynolds number of about 1.72 × 106 was considered based on the height of the pantograph, Hpt. To solve the flow field around the vehicle, an improved delayed detached eddy simulation (IDDES) with shear-stress transport κ–ω turbulence model was adopted. This method has the advantages of Reynolds-averaged Navier–Stokes and large eddy simulations (Spalart, 1997; Travin et al., 2002), and can partially resolve log-layer mismatches and grid-induced separation (Spalart et al., 2006
Analysis of unsteady aerodynamic forces
There are large scale-based differences among the vehicle components used in this study. If dimensionless processing is adopted in the aerodynamic forces of vehicle components, the aerodynamic coefficients of some smaller components will be too small. Therefore, in this section, we discuss about the use of aerodynamic forces directly for comparative analysis; this could help the reader assess the actual loads applied on these structures. To analyse the influence of plate configurations on
Conclusions
In this study, an aerodynamic analysis was performed on 1/8th-scaled uniform vehicles with three configurations of plates mounted at the inter-carriage region to enhance the vehicle’s braking mechanism. A numerical CFD study was adopted to find a more efficient plate configuration in terms of aerodynamic behaviour. An IDDES method with a κ–ω turbulence model succeeded in reproducing the main flow patterns and was verified experimentally.
This paper presents an analysis of the effect of the
CRediT authorship contribution statement
Jiqiang Niu: Conceptualization, Methodology, Formal analysis, Writing - original draft, preparation. Yueming Wang: Data curation, Writing - original draft, Software. Feng Liu: Visualization, Investigation, Writing - original draft, preparation. Zhengwei Chen: Validation, Writing - review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This study was supported by the National Natural Science Foundation of China (51805453), the Project funded by China Postdoctoral Science Foundation (2019M663551), the Fundamental Research Funds for the Central Universities (2682018CX14), the Sichuan Science and Technology Program (2020JDTD0012), and the Open Research Project of the National Key Laboratory of Traction Power (TPL1904).
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2021, Journal of Wind Engineering and Industrial AerodynamicsCitation Excerpt :The IDDES, which is a hybrid method combining the delayed detached-eddy simulation (DDES) and wall-modeled LES (WMLES), offers advantages for overcoming MSD and GIS, and for reducing the limitation of the Reynolds number for near-wall flow (Spalart, 2009). Therefore, in this study, we adopted the IDDES based on the shear-stress-transport (SST) k-ω turbulence model, which has been widely employed to study the aerodynamic characteristics of trains (Munoz-Paniagua et al., 2017; Niu et al., 2020; Wang et al., 2018b, 2020a). In Eq. (1), Cw is an empirical constant equal to 0.15 based on a wall-resolved LES of channel flow (Shur et al., 2008), dw is the distance to the wall, hwn is the grid step in the wall-normal direction, and hmax in Eq. (1) is defined as the largest local grid spacing, as shown in Eq. (2).