Pressure wave characteristics in high-speed maglev tunnels with various arch lattice-shell lengths inside hoods

With the increase in train speed, significant pressure fluctuations will occur inside the tunnel during the high-speed maglev train traveling through a confined tunnel, which causes the so-called sonic boom at the tunnel exit. An inner arch lattice-shell structure was proposed to be added into the existing enlarged cross section hood, to achieve the energy dissipation of pressure waves. This design has been proved to be more effective in alleviating the micro-pressure waves (MPWs) as compared to the conventional hoods. To explore how the length of the inner arch lattice-shells affects the MPWs, the three-dimensional, compressible, and unsteady simulations, combined with the sliding grid technology, were conducted in this paper. The evolution characteristic of the initial compression wave (ICW) generated at the hood/tunnel entrance and the emission feature of the micro-pressure wave emitted at the tunnel exit were simulated and analyzed. Additionally, the evolution characteristics and mechanisms of the flow field structure inside the hood and tunnel were examined. The results show that the inner arch lattice-shell can dissipate the energy of pressure waves. As the length of the inner arch lattice-shell increases, the two-step pressure curves of ICWs become smoother, largely reducing the peak value of the ICW pressure gradient and the MPWs. For a 100 m enlarged cross section hood, the longer the inner arch lattice-shell is, the more significant mitigation on the pressure gradient of ICWs is achieved. In addition, when the arch lattice-shell length has an increase from 60 to 80 m, the mitigation effect of the hood on the pressure gradient of ICWs is significantly enhanced; however, when the lattice-shell length further increases, this effect tends to be stable with a smaller increase in the mitigation ratio. The corresponding mitigation effect on the MPWs is observed. When the lattice-shell length is 100 m, the reduction in the MPW amplitude reaches 51.9% at 20 m and 44.0% at 50 m away from the tunnel exit.