Modern high-speed trains employ underfloor equipment cabins (ECs) to reduce underbody aerodynamic drag and to provide filtered air for cooling critical electrical components. Previous studies on the aerodynamics of high-speed trains have generally neglected the effects of EC ventilation. Therefore, this study investigates the aerodynamic influence of the cabin's ventilation by comparing two train configurations: one with equipment cabins (WEC) and a baseline model without equipment cabins (WOEC). Results show that EC ventilation significantly modifies aerodynamic performance, i.e., increasing drag, altering lift distribution, thickening boundary layers, and intensifying wake structures. The middle cars were most affected due to their downward air exhaust configuration. Middle car 1 experienced pressure increase on the bottom plate due to the traction motor fans, resulting in the positive lift, while middle car 2 developed suction zones near the transformer outlets, leading to the negative lift. These effects contributed to a 13.6% increase in total drag and a 14.3% reduction in lift for the WEC configuration. Flow analyses revealed that ventilation jets induced strong underbody disturbances through jet entrainment, suction, and downwash, leading to thicker, asymmetric boundary layers and enhanced shear near the ground. In the wake, the WEC case exhibited a deeper pressure deficit, larger vortical structures, and slower recovery than the WOEC model. The findings highlight that the aerodynamic penalties associated with ECs are non-negligible. Optimizing outlet placement, grille design, and implementing appropriate flow-control strategies is recommended to mitigate drag penalties and balance lift and to enhance the safety and energy efficiency of high-speed train operations.
Eze et al. (Thu,) studied this question.