| With the advancement of urbanization and the increasing tension of land resources,the urban fire risk is increasing.Especially the high-risk building fa?ade fire caused by the combustion of external thermal insulation materials has occurred frequently in recent years.A large number of fire accidents indicate that the combustion of external thermal insulation materials was caused by the flame ejecting from the facade windo ws.Compared to improving the flame retardancy of external thermal insulation material,it is an economical and feasible measure to prevent the ignition of the thermal insulation material from the ejecting flame and to improve the fire protection constructions of building fa?ade.Therefore,it has great practical significance to study the effect of fire canopy on flame ejecting behavior of building fa?ade wall.In this thesis,a series of reduced scale experiments and numerical simulation researches on the effect of fire canopy on flame ejecting were carried out.Flame ejecting preventing experimental platform in reduced scale of 1/5 was designed and established.Under a single fire power,a series of experiments of flame ejecting behavior on free boundary and different width of fire canopy conditions were carried out.The experimental results showed that for the evolution process of flame ejecting behavior,the combustion state of the recession stage was different under fire canopy and free boundary condition.The influence of fire canopy on the temperature in room was small,but the influence of fire canopy on temperature distribution of external facade was obviously.The axial temperature of fa?ade under fire canopy decreased linearly with the increase of height,and the inhibitory effect of fire canopy on the axial temperature was quantified.The radial temperature distribution of fa?ade under fire canopy condition was still Gauss distribution,but the maximum temperature and its corresponding radial distance changed with the width of fire canopy.Using the FDS numerical simulation software,a full-scale model similar to the reduced scale experimental model was established.On the basis of verifying the accuracy of the FDS simulation,the influence of the width,length and position of the fire canopy on the fire ejecting behavior was analyzed under different kinds of fire power.The simulation results showed that comparing the free boundary condition,the setting of the fire canopy may cause a very small reduction on the height of the neutral surface and not obviously affected the heat release rate and the temperature in room,which was in accordance with the experimental results.For free boundary condition,when ejected flame close to the fa?ade,the axial temperature of fa?ade decreased exponentially with the increases of height,otherwise,the axial temperature decreased linearly with the increase of height.Based on the analysis of the influence of the fire canopy width on the axial temperature,the width of fire canopy was more reasonable in the range of 1.0 ~ 1.6 m,and the dimensionless model of the maximum axial temperature of fa?ade was put forward.And through the analysis of the radial temperature distribution at various heights,it was found that the fire canopy had a push-off effect on the radial temperature distribution,and the recession trend of the maximum radial temperature at different heights was different.The maximum radial temperature decreased linearly at low altitude but decreased exponentially at higher altitude.In addition,based on the temperature-defined flame contour method,the accuracy of the ejected flame height on free boundary condition in FDS was verified by the Lee's model,and the dimensionless ejected flame height model under different width of fire canopy was proposed.Finally,based on the qualitative analysis of the effect of the length and location of fire canopy on flame ejecting behavior,increasing the length of fire canopy can restrain the flame ejecting from the side of fire canopy,and the location which closed to the edge of window was more reasonable. |
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