Flow-induced aeroacoustic characteristics of a simplified Hyperloop in low-vacuum tubes

Journal article, 2027

Operating high-speed trains within highly confined, low-vacuum tube environments induces complex choking effects and severe shock wave phenomena, generating intense aeroacoustic noise. In this study, the delayed detached eddy simulation (DDES) method, applied to a two-dimensional axisymmetric model, was employed to investigate the unsteady flow field and aeroacoustic characteristics of low-vacuum tube trains. Numerical accuracy and mesh independence were rigorously validated against wind-tunnel experimental data. Comparing three distinct flow regimes (subsonic unchoked, subsonic high-blockage-ratio choked, and supersonic choked) revealed how highly confined choking effects influence shock train propagation, multi-scale vortex shedding, and the overall aeroacoustic environment. Results demonstrated that aerodynamic noise predominantly originated from fluid-wall surface pressure fluctuations, alongside shock-vortex coupling induced by wake shear layer instability. Under subsonic unchoked conditions, macroscopic flow remained relatively stable, yielding a favorable aeroacoustic environment with minor wave-induced perturbations. Under the subsonic choked condition (0.4 blockage ratio), local airflow accelerated from 0.85 Ma at the head car of the train to 1.5 Ma at the middle car. This obstructed upstream noise propagation while complex shock-vortex interactions amplified downstream acoustic gradients, creating an "upstream-low, downstream-high" noise distribution with vertical overall sound pressure level (OSPL) discrepancies reaching 5 dB. Under the 1.2 Ma supersonic choked condition, freestream velocities surged to 1.5 Ma in the diverging section, generating intense, continuous shock trains. Their reflection and superposition maintained a consistently high OSPL throughout both upstream and downstream regions. By elucidating these quantitative impacts, this study provides critical theoretical support for enhancing passenger comfort.