Study On The Smoke Flow Characteristics And Temperature Distribution Of Y-shaped Subway Tunnel

With the development of urbanization,subway tunnel lines have become more diverse,among which Y-shaped subway lines are widely used in practice.Y-shaped subways can greatly alleviate the difficulty of passenger transfers,improve the efficiency of subway operation,and enhance the passenger travel experience.Compared with traditional subway interval tunnels,the smoke movement in Y-shaped subway interval tunnels is complex.When smoke passes through the junction,the path of smoke propagation changes.Therefore,studying the smoke flow characteristics and temperature distribution pattern of Y-shaped subway interval tunnels,proposing ventilation measures for optimization,has a certain reference significance for fire prevention and smoke exhaust design of Y-shaped subway tunnels in actual underground railway engineering.In this paper,literature review and fire design standards were consulted,and a scaled experiment was conducted to verify the reliability of numerical simulation.Based on this,the CFD(Computational Fluid Dynamics)numerical simulation method was used to study the smoke flow characteristics and temperature distribution of Y-shaped subway interval tunnels under different bifurcation angles,different fire source powers and positions.Based on this,the most unfavorable factors were selected to add longitudinal ventilation,propose reasonable ventilation optimization measures,and provide personnel safety evacuation suggestions.The main findings of this study are as follows:(1)Study on the reliability of numerical simulation verified by scaled experiments.A 1:15scaled experiment platform was built,and the experimental results were compared and analyzed with the numerical simulation results.The results showed that the temperature distribution pattern of the scaled experiment was basically the same as that of the numerical simulation,with an error within 15%,which verified the rationality of the boundary conditions and grid division of numerical simulation.(2)Study on the regularity of smoke flow characteristics under different working conditions.The influence of different fire source powers on smoke flow characteristics was small.When the fire source was located upstream of the junction,the smoke flow characteristics were basically the same for different bifurcation angles upstream of the fire source,and the smaller the bifurcation angle downstream of the fire source,the higher the smoke layer height and the lower the wind speed.When the fire source was located in the middle of the junction,the smaller the bifurcation angle on the left side of the main tunnel,the lower the smoke layer height,and the same visibility.The smaller the bifurcation angle at the branch tunnel,the higher the smoke layer height.When the fire source was located downstream of the junction,the smaller the bifurcation angle,the higher the smoke layer height.(3)Study on the regularity of temperature distribution under different working conditions.Different fire source powers had a great influence on temperature distribution,and the higher the fire source power,the higher the temperature distribution.When the fire source was located upstream of the junction,the temperature distribution was basically the same for different bifurcation angles upstream of the fire source,and the smaller the bifurcation angle downstream of the fire source,the lower the temperature distribution.When the fire source was located in the middle of the junction,the temperature at the ceiling and personnel characteristics decreased with decreasing angle,and the longitudinal temperature at the junction was basically the same.When the fire source was located downstream of the junction,the smaller the bifurcation angle,the lower the temperature distribution.(4)Study on optimization of ventilation measures.Based on the previous research,the most unfavorable factor was selected to add longitudinal ventilation in the main tunnel.The smoke propagation characteristics and temperature distribution for different bifurcation angles were compared and analyzed.The results showed that the one-to-one ventilation mode was more favorable in this simulation condition.After adding longitudinal ventilation,the smoke flow became chaotic and the overall temperature distribution decreased.Based on this,suggestions for ventilation measures and personnel safety evacuation were proposed.