Abstract: In response to the problems of mineral dust pollution and resource waste caused by the "piston wind" effect in heavy-haul railway tunnels,taking Liangjiashan Tunnel as the research object,the regulatory mechanism of the structural forms and key parameters (maximum/minimum cross-sectional area ratio r of the tapered section,taper angle β) of four pressure re lief and flow rectification devices (tapered-equal annular type,equal annular-tapered-equal annular type,tapered-beveled-equal annular type,equal annular-beveled type) on the tunnel entrance flow field was systematically explored through a combination of numerical simulation and experimental verification.The results show that the tapered-equal annular device reduces the pres sure gradient at the tunnel entrance and buffers the sudden change of wind pressure by contracting the flow channel in the ta pered section,and suppresses the generation of eddies by stabilizing the annular gap flow pattern in the equal annular section. Its comprehensive performance is better than that of multi-section combined or single beveled structure devices.When r≤1.4, the peak wind pressure decreases with the increase of r;when r>1.4,the pressure gradient rebounds.With the increase of β, the guiding effect of the side wall of the tapered section on the air flow is enhanced,and the pressure gradient is released more fully along the process,avoiding the concentrated accumulation of pressure at the tunnel entrance.Based on the field reality of Liangjiashan Tunnel,r=1.4 and β=20° are optimized as the optimal structural forms of the pressure relief and flow rectifica tion device.Engineering verification shows that the application of the device with the optimal structural form can reduce the maximum wind pressure in the tunnel by 60~100 Pa and the mineral dust concentration by 70%~90%,which can effectively control the "piston wind" effect and provide a parameter design basis for similar projects.

Key words: heavy-haul railway tunnels,pressure relief and flow rectification device,structural form,numerical simula tion,flow field