Yaw angle impact on high-speed train–flat box girder aerodynamics

Flat box girders are widely used in large-span bridges to accommodate high-speed trains, owing to their cost-effectiveness and vibration stability. However, their aerodynamic stability remains a critical issue that has received relatively little attention, especially when coupled with a train to form a train–flat box girder (train/bridge) system. Therefore, this study conducted a numerical simulation of a train/bridge system to analyze the flow field, drag coefficient (CD), lift coefficient (CL), and moment coefficient (CM) of the train. Numerical results revealed complex and significant aerodynamic interactions within the system, with stronger disturbances and more pronounced flow separation when the train was positioned on the windward side of the bridge. Both CD and CL of the head and middle cars increased with yaw angle, showing two distinct phases: a gentle variation interval (0°–15°) and a linear increase interval (20°–70°). However, in the 75°–90°-range, the CD of the middle car on the windward side of the bridge surged abruptly, whereas CL dropped sharply. Meanwhile, the CM of the head and middle cars gradually decreased with increasing yaw angle; however, the CM of the middle car on the windward side suddenly decreased when the yaw angle exceeded 75°.