A Study Of Characteristic Of The Fire Smoke Flow In Spiral Tunnels

With the development of tunnels in China,the spiral tunnels with titled slope,whose radius of curvature become increasingly smaller,have appeared,because of the terrain and engineering.However,the situations of fire that occur in spiral tunnels is different from those in the linear tunnels,causing the difference of the law of fire spread in spiral tunnel.Therefore,the studies of smoke spread in the fire of spiral tunnels have theoretical values and practical value for tunnel design and fire rescue.Numerical simulation and theoretical analysis are carried out in the paper with the research targets of different tunnels(titled tunnels,curved tunnels and spiral tunnels),and the main research contents are as follows:(1)The research on the method of smoke exhaust in sloping tunnels is helpful to rescue and escape in the tunnels fire.In order to research the method of smoke exhaust about tilted tunnels fire under the condition of semi-transverse ventilation,the numerical simulation is adopted to simulate the process of tunnel fire in the paper,analyzing the rule of the coefficient of λ(uniformity coefficient of smoke exhaust range)and α(the thermal efficiency of smoke exhaust)at the different smoke-exhaust method.Results show that when the slope is 0%-1.5%,the standard of smoke exhaust could control the smoke to spread effectively in the tunnel;When the slope is more than 1.5%,smoke along the downslope direction could be controlled near exhaust port due to the effect of buoyancy,so the method of unilateral smoke exhaust in the upslope direction is adopted to exhaust effectively and improve heat efficiency of smoke exhaust of fans;But when the slope is more than 3%,the smoke exhaust rapidly escape from exhaust port and spread to the tunnel exit because of the chimney effect which makes the smoke exhaust in the tunnel spread with tremendous speed,so longitudinal ventilation should be added to restrain the reflux of smoke exhaust in the upslope direction,which restricts the spread of the smoke exhaust better.(2)The numerical simulation methods are also used to study the flow of smoke in the curved tunnel with different curvatures to analyze the range and extent of the influence of curvature of curved tunnel by combing force magnitude of smoke with the geometric structure of curvature.The results show that the values of smoke temperature and velocity at outer side which is near to the centerline of fire source of curved tunnel are higher than those at inside which is equidistant from the centerline of fire source,and the difference increases with the increase of the curvature.What’s more,the magnitude of the fire power will change the critical value of R,and the critical value of R also increases with the fire power.(3)The numerical simulations are carried out on fire of spiral tunnels with different titled slope and radius of curvature,and the compared analyses are carried out between fire of spiral tunnels and titled tunnels as well as curved tunnels.As the results show,the effect of chimney effect that which can promote the smoke flow in the uphill direction and inhibit the smoke flow in the downhill direction on the smoke spread in tunnel is applicable to both the titled tunnel and spiral tunnel.Furthermore,the chimney effect works more effectively with the increase of the titled slope.The influence of curvature in the fire of spiral tunnels on the range of smoke spread is similar to the fire of curved tunnels,but the impact effect of curvature makes a difference,for the chimney effect of fire of spiral tunnels in the uphill direction leads to a phenomenon that velocity and temperature difference of smoke at both inside and outside will increase first and then decrease.Theoretical research can provide reference for the design of spiral tunnel fire control in this paper.