Effect of cowcatcher surface roughness height on aerodynamic performance of high-speed trains

As the operating speed of high-speed trains increases, the proportion of aerodynamic drag in total drag gradually rises. Currently, employing micro-structured units on the train surface represents a novel approach for drag reduction in high-speed trains. The cowcatcher at the bottom of the head car is significantly affected by airflow impact. The highly turbulent vortex structures generated there influence downstream components. However, applying micro-structured units across the train surface consumes substantial resources. Therefore, a roughness function is adopted to represent these micro-structured units. Numerical simulations are conducted to study the influence of cowcatcher surface roughness heights (0.5 mm, 0.7 mm, and 1.0 mm) on the aerodynamic characteristics of the train underbody. The results indicate that variations in cowcatcher surface roughness height significantly affect the underbody flow field. The rough surface reduces the underbody flow velocity, consequently decreasing the pressure distribution on downstream components, particularly the pressure intensity on the windward plates of the bogie region. Regarding aerodynamic drag, the drag reduction rates in the Bogie 1 region are 15.13%, 19.29%, and 18.69% for the different roughness heights, respectively. The optimal drag reduction effect in the Bogie 1 region occurs at a roughness height of 0.7 mm. This is attributed to the roughness height in the cowcatcher region reducing the velocity of airflow entering from the cowcatcher bottom, thereby mitigating the impact of high-speed airflow on the downstream bogie region and consequently reducing its aerodynamic drag. The findings of this study provide guidance for the future research of higher-speed trains.