Influence of a centralized air chamber on the evolution of compression waves in high-speed railway tunnels

To investigate the regulation mechanism of pressure gradients during the propagation of initial compression waves in high-speed railway tunnels by centralized air chambers, and to analyze the influence laws of the air storage effect of the air chamber and the geometric characteristics of the connection on the propagation characteristics of compression waves, numerical calculation studies on the tunnel-chamber coupled dynamic interaction were carried out based on an inviscid, compressible, and two-dimensional axisymmetric model, and a pressure regulation theory involving the synergistic effect of the air storage effect and damping characteristics was proposed. Based on the flow similarity criterion, scaled model tests of an adjustable high-pressure pulse generator were conducted. By comparing the numerical simulation results with the model test results, it was verified that the adopted calculation method could accurately simulate the dynamic response characteristics of the initial compression wave passing through the air chamber. The influence laws of key dimensional parameters of the air chamber on its air storage capacity and the damping characteristics of the connection were deeply analyzed, and the flow response mechanism driven by the pressure difference between the air chamber and the tunnel was explored. By comparing different air chamber sizes and connection sizes, the relief laws of the air chamber structure on the pressure gradient of the initial wavefront were further studied. The influences of wavefront parameters, such as the length and amplitude of the initial compression wave, on the relief effect of the air chamber were analyzed. Research results indicate that the pressure gradient relief mechanism of the centralized air chamber stems from its ability to absorb air when the initial compression wave passes through, and the connection size is a key factor in regulating the air flow response speed from the tunnel into the air chamber and the damping characteristics. When the connection size is 0.40R, and the air chamber size is R, the air chamber exhibits characteristics of high flow accompanied by moderate reflux, corresponding to an optimal relief rate of about 40%. Changing the amplitude of the initial compression wave does not affect the relief rate of the air chamber, while the length of the compression wave is strongly negatively correlated with the relief rate. When the wavelength is shortened, the relief rate of the air chamber significantly increases, and when the wavelength is constant, the relief rate remains stable.