• Tunnel conditions amplify total sound source energy by 5.26 times compared to open air, with significant increases in tail car, bogies, and pantograph.
• Bogie noise dominates in the 50–1000 Hz range, while pantograph noise peaks at 1500–2500 Hz, with tunnel effects enhancing low and medium frequency bands.
• Radiated acoustic energy on roof and side surfaces is amplified by 33.3 and 22.6 times in tunnels, far exceeding hydrodynamic amplification factors of 8.6 and 6.3.
• The study provides coupled flow-acoustic mechanisms that support noise reduction design for high-speed trains in tunnels.