Aeroacoustics of the bogie region of high-speed trains in a tunnel: Dual-mode competition and harmonic enhancement

To investigate the influence mechanism of the tunnel environment on aerodynamic noise in the bogie region of high-speed trains, numerical simulations based on the Delayed Detached Eddy Simulation model are performed on a simplified cavity-bluff coupled configuration. The flow and acoustic field characteristics under both open-air and tunnel conditions are compared and analyzed. The results show that, under the open-air condition, the flow in the bogie region is dominated by the primary vortex shedding mode originating from axles and rods. Under the tunnel condition, the energy proportion of this primary mode decreases, while a secondary flow mode is excited. This secondary mode originates from the coupling between the tunnel annular cavity mode and the bogie cavity standing-wave mode and generates the second and third harmonics through nonlinear fluid distortion. These mechanisms lead to a concentration of acoustic energy in the mid-to-high frequency range under the tunnel condition, resulting in significant narrowband peaks. Consequently, both the overall surface sound power level and the near-field overall sound pressure level in the bogie region are higher than those under the open-air condition.