Research on the influence of wake effects within train groups operating at small spacing

The operation of heavy-duty train groups is emerging as a potential development trend for future railway transportation. Compared to single-train operation, trains running in groups at small spacing often result in situations where the front end of a following train approaches to the rear end of the preceding train, leading to changes in the aerodynamic characteristics of the following train. This paper presents a comparative study on the aerodynamic performance of heavy-duty trains with and without a preceding train, focusing on single-train operation versus group operation of trains at a 200 m spacing, both at 80 km/h. Based on a simplified model of a five-car formation consisting of a typical locomotive and open wagons, a calculation method that combines steady and transient states was utilized, leveraging the SST <italic>k</italic>-ω turbulence model and the IDDES turbulence model based on SST <italic>k</italic>-ω. The research results indicate that, compared to single-train operation, the group operation of trains can effectively reduce aerodynamic resistance for trains starting from the second position in the group. At 80 km/h, the aerodynamic resistance to following trains decreased by 8.30%, with reductions of 9.05% for head cars and 7.91% for tail cars. A clear long-distance wake drag zone is identified at the rear end of preceding trains during group operation. This zone extends downstream and merges with the boundary layer of the following trains at the front of their head cars, creating a low-speed area connecting the preceding and following trains. As a result, the impact of high-speed airflow on the front end of the following trains is significantly reduced. In addition, the positive pressure zone at the front of the second train during group operation experien-ces a slight pressure decrease, indicating that the wake of the preceding train can effectively reduce the positive pressure distribution zone formed by the airflow impact on the following train during operation. The pressure distribution on the carbody surface exhibits similar characteristics, as the strong positive pressure zone created by airflow impact on the head car surface is somewhat alleviated. Therefore, operating train groups can effectively improve aerodynamic characteristics during train operation, offering an option to further reduce energy consumption and enhance the efficiency of heavy-duty train operation.