Study On Fire Smoke Flow Region And Numerical Calculation Range Length Of Highway Tunnel

Research on tunnel fire smoke flow parameter in different area is used to determine the influence of different flow region and numerical calculation range length.It is of great significance to improve the theoretical system of tunnel fire smoke transportation and optimize the parameters of modeling.In this paper,the numerical simulation and theoretical analysis were used to study on the division of fire smoke flow area and numerical calculation range length of highway tunnel.The main research work and results are as follows:(1)The near-field region length of the highway tunnel was studied.Firstly,temperature data of the center-line under the ceiling wall and the side wall along the tunnel were obtained by the method of numerical simulation.Based on this,It is proposed that the difference of temperature gradient less than 1?/m was used as the dividing criteria of the near-field region and the far-field region.Secondly,The influence of heat release rate,tunnel section geometry and fire source geometry on the length of near-field was analyzed.Lastly,a model for predicting the length of near-field under the coupling effect of heat release rate and tunnel section geometry was established.The length of the dimensionless near-field region L*is linearly increasing with the 2/5 of the dimensionless source power Q~*.(2)The smoke layer disorder region length of the highway tunnel was studied.Firstly,smoke layer data was obtained by the method of numerical simulation.The morphologic change of smoke layer in the far-field region of tunnel was analyzed.Based on this,The far-field can be divided into two regions:the one-dimensional flow region and the smoke layer disorder region.Secondly,Froude number was introduced to quantitatively analyze the relationship between the inertia force and the thermal buoyancy force of the smoke layer in the far-field region.The length of smoke layer disorder region was determined.Thirdly,the influence of heat release rate and tunnel section geometry on the length of smoke layer disorder region was analyzed.Lastly,a model for predicting the length of the smoke layer disorder region under the coupling effect of HRR and tunnel section shape was established.The length of the dimensionless smoke layer disorder region L*is linearly increasing with the 2/5 of the dimensionless source power Q~*.(3)The numerical calculation range critical length of the highway tunnel was studied.Firstly,the average temperature of the smoke layer and the smoke mass flow data were obtained by the method of numerical simulation.Based on this,a critical criterion for selecting numerical calculation range critical length of highway tunnel is presented.Secondly,The influence of heat release rate and tunnel section geometry on the numerical calculation range critical length is analyzed.Lastly,The linear growth relationship between the numerical calculation range critical length L_d and the mesh size D*was obtained.A formula for calculating the numerical calculation range critical length is established,which is convenient for engineers to obtain the required tunnel model length directly according to the mesh size.