Investigation of the transient aerodynamic characteristics of a twin-car system during same-direction following operation

During same-direction following operation of a twin-car system, the trailing car is continuously exposed to the wake disturbance generated by the leading car, which may affect aerodynamic-load stability and horizontal ride comfort. To investigate this problem, a three-dimensional transient aerodynamic model of an ultra-high-speed twin-car system was established and partially validated using local airflow-velocity measurements. Unsteady numerical simulations were conducted using dynamic mesh layering. The baseline configuration includes a 120 m enclosed hoistway with initially stationary air and two cars with dimensions of 1.95 × 1.8 × 2.5 m3 and a cross-sectional area of 3.51 m2, operating at a maximum speed of 7 m/s. The spatiotemporal evolution of the airflow within the hoistway, the spatiotemporal distributions of airflow velocity and pressure in critical wall regions, and the evolution mechanisms of car drag, lateral lift, and surface pressure were systematically analyzed. The effects of tracking distance and acceleration on the aerodynamic characteristics were further investigated. The results show that, as the tracking distance increased from 6.5 to 7.5, 8.5, and 9.5 m, the peak negative drag coefficient of the trailing car increased by 6.67%, 12.64%, and 18.55%, respectively. When the acceleration increased from 1.0 to 1.25, 1.50, and 1.75 m/s2, the peak lateral lift coefficient of the trailing car increased by 14.28%, 21.90%, and 30.47%, respectively. This study provides a theoretical basis for a comfort-oriented design and operating-parameter optimization of twin-car systems and offers engineering guidance for improving ride comfort.