Variations in heat transfer and fluid flow around the axle-mounted C/C–SiC brake disc of high-speed trains

Purpose During emergency braking at 400 km/h, a high-speed train’s C/C–SiC brake disc can cause a significant rise in the temperature of the surrounding air, posing potential safety risks. Given the difficulties in direct measurement of thermal profiles in underbody airflow, the purpose of this study is to investigate the transient temperature variations in both the brake disc and nearby air. Design/methodology/approach A fully coupled fluid–solid–thermal model, incorporating the train head, bogie and brake disc, is developed to simulate heat generation and transfer under actual braking conditions. Bench tests of C/C–SiC brake discs are conducted to validate the computational accuracy of the simulation model. Findings During braking, the disc reaches a peak temperature of 1,122.8 K, whereas post-braking natural convection forms a high-temperature zone above the disc, peaking at 630 K. The area with air temperature above 400 K expands from 0.0248 m² to 0.3100 m² along the flow direction, an 11.5-fold increase. Over time, the high-temperature area (>400 K) enlarges from 0.69 m² at 120 s to 5.66 m² at 150 s, with the >500 K region increasing by approximately 27%. These results reveal a pronounced directional heat propagation and the formation of a >600 K hot zone near the undercarriage, posing a potential thermal hazard. Originality/value This study implements a thermal–fluid–solid coupling simulation approach for high-speed train brake discs, enabling real-time acquisition of temperature variations. The demonstrated adaptability of this methodology allows its extension to brake disc thermal analysis in diverse domains such as automotive vehicles and mining locomotives.