Abstract
This paper numerically computed the problem of pressure fluctuations in the open air and tunnel based on the virtual computer technology, and experimentally verified the correctness of the numerically computational model. In the open air, pressure fluctuation at the nose tip of train head was serious and presented two obvious valley and peak values. Pressure at the nose tip of train tail did not present obvious fluctuations. Pressure at the train head was obviously more than that at the train tail. For different observation points, the peak and valley values of far-field pressures only showed translation with the increased running time. In the tunnel, pressures at the nose tip of train head had obvious peak and valley values and were far more than those in the open air. For different observation points, the peak and valley values of far-field pressures did not simply present translation with the increased running time, which indicated that there was wall effect in the tunnel. In addition, the absolute values of the maximum positive and negative pressures of the high-speed train in the near and far fields obviously increased with the increased running time. The pressure fluctuation caused by the high-speed train in the tunnel was the superposition of the inlet pressure wave and air disturbance caused by the passing train. The size of local air pressure was related to tunnel length, train length and speed. The peak value of positive pressures in the tunnel appeared when the train entered the tunnel. The valley value of negative pressures in the tunnel would appear in the area where the expansion wave of train head was superimposed with the compression wave of train tail. According to tunnel length, train length and speed, the specific positions where the peak and valley values of positive and negative pressures appeared could be approximately obtained. If the tunnel was very long, it was possible to present the peak value of positive pressures caused by the superposition of more continuous compression waves or the valley value of negative pressures caused by the superposition of more continuous expansion waves.
Highlights
When a high-speed train enters a tunnel suddenly from the open air, space around the train will be small and air pressure will rise
When train tail enters the tunnel, the space occupied by the train body at the tunnel is suddenly released and air squeezed by the train body at the tunnel inlet is released, which suddenly reduces pressure and forms an expansion wave
It is shown in the figure that: when the blocking ratio was smaller than 0.22, obvious linear relations were between the pressures on the train surface and the blocking ratio; pressures gradually increased with the increased blocking ratio as the increase of blocking ratio will improve effects of compression waves and expansion waves when the train entered and left the tunnel
Summary
When a high-speed train enters a tunnel suddenly from the open air, space around the train will be small and air pressure will rise. Luo [6] adopted an aerodynamic model to study the propagation mechanism of transient pressure of a high-speed train in the process of entering a tunnel with buffer structure. Based on one-dimensional compressible unsteady flow model and the parameter characteristics of tunnel section, Mei [16] studied the characteristics of pressure fluctuation of a single train passing through a super-long tunnel with simple structure, and concluded the influence of tunnel length, train speed and air tight index on pressure in the train. Based on CFD software, Xu [18] adopted the pressure correction algorithm of three-dimensional compressible unsteady turbulent flow models and the grid technology of arbitrary sliding interfaces to conduct a numerical simulation for the pressure waves of the high-speed train which met in a tunnel at a constant speed and a non-constant speed, respectively. The specific positions of the peak value of positive pressures and the valley value of negative pressures could be obtained through analyzing the pressure fluctuations in the tunnel under different speeds
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