Flow control for aerodynamic drag reduction of a high-speed train with diversion slots on bogie regions

A diversion slot is one of the potential mechanical devices to reduce high-speed train underbody aerodynamic resistance. This research aims to investigate the effectiveness of using diversion slots as a means of passive flow control to reduce the resistance of a high-speed train. Two different diversion slot designs, i.e., the big diversion slot (Bds) and the small diversion slot (Sds), placed at two installation locations near the bogie cabin end walls in six configurations are used. The results indicate that drag of the tail car is significantly reduced by 7.8%, 5.5%, 9.0%, and 9.4% using the configurations in cases 2 and 4-6, while an increase in 0.4% is experienced in case 3. Consequently, the total train aerodynamic resistance reduces by 1.9%, 0.2%, 3.0%, 4.2%, and 0.4% in cases 2-6, respectively, as compared to case 1. By evaluating the flow structure, we found that the diversion slots trigger flow separation, deflecting the airflow from entering the bogie regions, increasing flow turbulence and reducing the flow velocity. It efficiently improves the wake flow structure by reducing the wake strength, thereby increasing the tail nose surface pressure, thus reducing the tail car's aerodynamic drag. This study proposes a novel approach for reducing aerodynamic drag in high-speed trains, improving the underbody flow and wake characteristics.