Aerodynamic drag and noise reduction of a pantograph of high-speed trains with a novel cavity structure

The design of the cavity structure is one of the effective means to reduce the resistance and noise of the pantograph installed on the roof of a high-speed train. This research first investigated the flow and acoustic characteristics of a pantograph with four different cavity structures, namely the rectangular cavity (original), the rounded edge cavity (case 1), and the other two rounded edge cavities with asymmetric (case 2) and symmetric (case 3) connecting tubes. The results show that the three cavity treatment methods all improve the aerodynamic performance, and the cavity model of case 2 is determined to be the optimal structure. In case 2, the tube installed at the front of the cavity destroys the separated shear layer and reduces the unstable airflow, reducing cavity resistance and noise by 9.64% and 5.2 dBA (A-weighted decibels), respectively. The pantograph is placed inside the previously determined improved cavity, which reduces the airflow velocity and the recirculation region upstream of the pantograph, decreases the impingement on the components in the middle and lower regions of the pantograph and the generation of highly intense vortices, and improves the wake structure and flow separation at the rear surface of the cavity. Thus, the aerodynamic drag for the pantograph and the whole system is reduced by 3.82% and 3.25%, respectively, and the aerodynamic noise is also decreased by 1.4 and 1.9 dBA, respectively. This study provides a novel structural design for the pantograph cavity region.