Analysis of unsteady flow field and near-field aerodynamic noise for rapid metro trains in tunnels by the hybrid improved delayed detached eddy simulation and acoustic perturbation equations method

To investigate the blocking effects and acoustic reflections in tunnels on the unsteady flow field and aerodynamic noise sources of rapid metro trains, this study employs a hybrid improved delayed detached eddy simulation and acoustic perturbation equations method to simulate the near-field noise of a 1/20 scale model metro train within a tunnel. The numerical approach is validated against wind tunnel experiments conducted with a high-speed train scale model. Results show that the blocking effect significantly increases the overall flow speed and elevates the train surface's total turbulent pressure and power levels, with the highest value reaching 132.67 dB at the head car. Additionally, three cases are studied: a tunnel with fully reflective walls, a tunnel with fully absorptive walls, and open-air conditions. Results demonstrate that the blocking effect primarily raises the overall total sound pressure level, while acoustic reflection further amplifies the sound and causes the sources to concentrate toward the middle of the train. The majority of the difference in sound power level between the tunnel and open air is attributed to the blocking effect, which accounts for up to 68.28%. Frequency spectra of sound pressure analysis reveal five peaks in the tunnel with fully reflective walls—260, 500, 850, 2490, and 3430 Hz—where Bogies 3 and 5 exhibit the highest power spectral density values of 124.55 and 124.91 dB/Hz, respectively. These findings provide valuable insights for future noise control strategies on rapid metro trains.