Study Of Flame Characteristics And Wall Temperatures Of Double Fires In Urban Tunnels

With the continuous popularization of tunnel traffic,the increasing number of tunnel fire accidents has caused serious harm.A thorough understanding of the basic flame characteristics of tunnel fires is helpful for fire prevention,as well as for tunnel repair and maintenance after disasters.Based on previous research on tunnel fires,this thesis uses small-scale experiments,theoretical analysis,and numerical simulation methods to study the morphological characteristics of double fires flames,temperature characteristics of the near fire field,and temperature field on the tunnel wall under the action of double fires.Based on the study of the morphological characteristics of double fires in tunnels,an empirical formula for the relationship between the flame merging probability Pm at different lateral positions and the spacing characterization parameter s* is given,and it is found that there is a "sensitive interval",that is,within this interval,slightly increasing s*can greatly reduce the value of Pm.Compared to the fires located on the central axis of the tunnel,there are more restrictions at the position attached to the wall,making the height of the flames double of double fires at the wall attachment position 15% to 17%higher than that at the same fire spacing on the central axis.At the same time,in the study of the flame height of double fires with different spacing at the central axis and the location attached to the wall in the tunnel,it was found that the maximum flame height of double fires was 1.43 to 1.62 times that of a single fire.In this study,empirical formulas for the flame height at the central axis position and the position attached to the wall are derived,and the variation rule of the flame height with s/D is obtained.The fires spacing corresponding to the minimum flame height is also obtained.Based on the study of the near fire temperature field of double fires,the reasons for the influence of double fires at different lateral positions and distances on the maximum temperature rise of the ceiling are described in detail,and an empirical formula for the maximum temperature rise of the ceiling suitable for this tunnel model is given.The study found that the vertical temperature rise distribution under dual ignition conditions is mainly affected by flame merging,while the distance between ignition sources is the main influencing factor for flame merging,while the lateral position has an impact on but does not play a major role in flame merging.The empirical formula of dimensionless temperature rise and dimensionless longitudinal distance after longitudinal normalization is derived,and the longitudinal temperature attenuation law of the ceiling is obtained.Based on the study of the characteristics of the temperature field on the ceiling,side walls,and ground of the tunnel under the action of double fires,the location of the highest temperature region on the tunnel wall at different lateral positions of the double fires is given.The relationship between the wall temperature and the distance between fires is also explored.Fig.65 Table 13 Reference 98...