Study On Characteristics Parameter Of Ceiling Jet And Smoke Control In A Longitudinal Ventilated Tunnel With Lateral Concentrated Smoke Extraction

In recent years,with the further development of the transportation,the highway tunnels in district,crossing the river and sea have continuously emerged,which has greatly improved the efficiency of people's travel and transportation.But what follows is the safety operation of the tunnel.Especially,tunnel fires usually cause heavy casualties and economic losses because of their great hazards,difficulty in evacuation and rescue.The development plan for the modern integrated transportation system during the “Thirteenth Five-Year Plan” clearly puts forward key research and development directions of long tunnel in the field of safety emergency.However,there are still no systematic guidelines having been formed for the anti-smoke design of the cross-sea or cross-river tunnels.Thus,this dissertation takes the control of lateral concentrated smoke extraction in the cross-sea or cross-river tunnel fires as the research object,through the model-scaled experiments of tunnel fire and theoretical analysis,the development of fire,smoke layer diffusion laws and smoke control under the combination of longitudinal ventilation and lateral concentrated smoke extraction were analyzed and studied.The following shows the main research contents of this paper:Firstly,the evolution of the characteristic parameter of heat fluxes received on the ceiling and floor induced by the tunnel fire plume are studied through experiments.It shows that heat fluxes received both on the ceiling and floor decay with the increasing of the longitudinal distance from the fire source.Through the dimensional analysis,the prediction correlations of the heat flux distributions received on the ceiling and floor are established respectively.And the model for predicting the maximum heat flux of the ceiling induced by strong and weak plumes were also established through theoretical analysis.Secondly,this paper studies the characteristics of smoke thermal stratification in tunnel fires with the combination of longitudinal ventilation and lateral concentrated smoke extraction,and puts forward the smoke layer stability criterion.It can be found that the increasing of lateral concentrated smoke extraction velocity will reduce the shear strength between the smoke layer and the air,which is conducive to maintaining the stability of the smoke stratification,and at the same time the relationship between the Froude number and the stability of the smoke stratification: when Fr(27)0.6,the smoke stratification is obvious and stable with an apparently smooth interface;when0.6 ?Fr(27)0.85,the interface becomes blurred and vortices appeared,but overall the smoke stratification is stable;when Fr ?0.85,there is no obvious smoke stratification,the stability of the smoke thermal stratification is destroyed.Finally,an experimental study of the smoke back-layering behavior under the combination effects of longitudinal ventilation and lateral concentrated smoke extraction was conducted to reveal the variations of smoke back-layering length and critical velocity.The results show that before the confinement velocity,the smoke back-layering length basically decreases with the increase of the lateral concentrated smoke extraction velocity,but after the confinement velocity,due to the interaction of the “lateral suction force”,longitudinal ventilation inertia and thermal buoyancy of combustion,a significant increase in the smoke back-layering length with the increase of lateral concentrated smoke extraction velocity can be observed,and the critical velocity also shows an increasing trend with the increase of lateral concentrated smoke extraction velocity.Through theoretical analysis,a prediction model of critical velocity induced by a tunnel fire with combination of longitudinal ventilation and lateral concentrated smoke extraction was established.