Improved delayed detached-eddy simulation on aerodynamic characteristics of biomimetic Coleoptera pantograph deflectors installed on a high-speed train

With continuous increase in the train speed, the aerodynamic drag forces of high-speed trains increase sharply in a square relationship. As an important source of train aerodynamic drag, pantograph regions have become the key areas to share the contribution to the train's total drag. Thus, improving the pressure distribution in pantograph regions can be a potential and effective method to reduce train aerodynamic drag. Coleoptera has smooth and hard elytra to protect the hindwings, which provides a new design concept for the pantograph deflectors. Based on the biological pattern of Coleoptera, the geometric shape of pantograph biomimetic elytra (i.e., deflector) was constructed in a three-car group mode. Therefore, four calculation cases were set up, i.e., the original unraised pantograph model, original raised pantograph model, unraised pantograph + deflector model, and raised pantograph + deflector model. A time-dependent numerical method improved delayed detached-eddy simulation (IDDES), first validated by the previous wind tunnel test, was employed to analyze the aerodynamic drag forces in different schemes, and the drag reduction mechanism of deflectors was studied. The results show that although an extra drag force is introduced from the deflector, a larger drag reduction is obtained from the pantograph itself. Thus, the aerodynamic drag of pantograph regions is significantly reduced after installing pantograph deflectors. The air flows over the pantograph region in a smoother way with less blocking effect, and the flow above the deflector is accelerated. After the deflector separately installed on three-car high-speed train models with unraised/raised pantographs, the drag reduction for the unraised/raised pantograph regions can be up to 83.88% and 35.29%, while for a three-car grouping model, it can be achieved by 10.76% and 4.49%, respectively.