Numerical research on two typical flow structures and aerodynamic drag characteristics of blunt-nosed trains
International Journal of Numerical Methods for Heat & Fluid Flow
ISSN: 0961-5539
Article publication date: 16 January 2025
Abstract
Purpose
This study aims to provide new insights into aerodynamic drag reduction for increasingly faster blunt-nosed trains, such as urban and freight trains. Specifically, this work investigates two distinctly different wake structures and associated aerodynamic drag of blunt-nosed trains.
Design/methodology/approach
Three typical cases of blunt-nosed trains with 1-, 2- and 3-m nose lengths are selected. The time-averaged and unsteady flow structures around the trains are analyzed using the improved delayed detached eddy simulation model and proper orthogonal decomposition method.
Findings
The simulation results indicate that for 2- and 3-m nose lengths, the flow separates at first and then reattaches to the slanted surface of the tail, with a pair of longitudinal vortices dominating the wake. In contrast, for the 1-m nose length case, the wake structure is characterized by complete separation, attributed to the larger curvature of the slanted tail surface. Consequently, the total time-averaged drag coefficient is reduced by 27.2% and 19.2% for the 1-m nose length case compared to the 2- and 3-m cases, respectively. Moreover, the predominant unsteady structures with Strouhal numbers St = 0.30 and St = 0.28 are detected in the near-wake of the 2- and 3-m nose length cases, respectively. These structures result from periodic vortex shedding at the lower slanted tail surface. In contrast, for the 1-m nose length case, the predominant unsteady structure with St = 0.19 is induced by the nearly periodic expansion and contraction of the upper bubbles.
Originality/value
Two distinctly different wake structures in blunt-nosed trains are identified. Unlike high-speed trains with longer, streamlined noses, for blunt-nosed trains, shorter nose lengths result in lower aerodynamic drag. Insights for reducing energy consumption in blunt-nosed trains are provided.
Keywords
Acknowledgements
This work was supported by Graduate Student Independent Innovation Project of Hunan Province (Grant No. CX20220281). The authors are grateful to the High Performance Computing Center South University for partial support of this work.
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.
Declaration of interest statement: This manuscript has not been published or presented elsewhere in part or in entirety and is not under consideration by another journal. The authors have read and understood your journal’s policies, and we believe that neither the manuscript nor the study violates any of these. There are no conflicts of interest to declare.
Data availability: The data that support the findings of this study are available from the corresponding author upon reasonable request.
Citation
Zhong, S., Yang, M., Qian, B., Zhang, L., He, D., Lin, T. and Lien, F.-S. (2025), "Numerical research on two typical flow structures and aerodynamic drag characteristics of blunt-nosed trains", International Journal of Numerical Methods for Heat & Fluid Flow, Vol. ahead-of-print No. ahead-of-print. https://doi.org/10.1108/HFF-10-2024-0767
Publisher
:Emerald Publishing Limited
Copyright © 2024, Emerald Publishing Limited