Evolution Behavior Of Overflow Flames On The Facade Of Parallel Buildings Under Leeward Vortex Effect

With the acceleration of urbanization in China,urban construction has entered a stage of stable development,exhibiting characteristics such as high density,large volume,and clustering,which has caused problems in the wind environment and fire of building clusters.The current research on the two aspects is relatively independent,and the impact of the leeward vortex flow field formed by the obstruction of buildings on the evolution of building facade fires is more complex than the spread behavior of building facade fires under the influence of a single direction wind environment.Therefore,this article mainly studies the evolution law of exterior overflow fire under the leeward vortex effect,and the research results have positive reference significance for performance-based fire prevention design,emergency rescue and disaster relief of buildings.The research work of this article mainly includes two parts: building cavity fire and exterior facade fire spread behavior.The specific research content and conclusions are as follows:(1)Four types of vent sizes and five types of fire source power conditions were established to study the prevalence of cavity fire overflow under different ventilation factors and fire source power synergy.By analyzing and comparing factors such as measurement point temperature,flame length,and flame behavior,it was found that the synergistic effect is reflected in combustion efficiency η Different,as the power of the ignition source and ventilation factor increase,η Showing a parabolic variation pattern;And by analyzing the slope k of the heat release rate curve,it is shown that the change in ventilation factor is more significant for chamber fires than the change in fire source power.(2)Using multiple comprehensive linear regression method and combining with the behavior of cavity flames,the phenomenon of flashover and weak flashover inside buildings under leeward vortex effect was compared and analyzed.Both flashover and weak flashover exhibit indoor high temperature environments accompanied by flame overflow,but flashover occurs in fuel controlled fires,forming a stable high temperature environment between 600 and 800 ℃,while weak flashover occurs in ventilation controlled fires with a short duration,and the high temperature environment is limited to around 500 ℃.(3)Explore whether there is a facade fire when the insulation material EPS and superstructure are fuel controlled fires.In the facade flame development stage,the temperature rise rate of the insulation material EPS during combustion is 3.61 ℃/s,2.3times that of the non insulation material combustion.The maximum temperature of the facade environment is also about 100 ℃ higher.Both cases can ignite the superstructure,but if the superstructure is a fuel controlled fire,the possibility of ignition is small.(4)Considering the impact of 0-5m/s upwind on the evolution of the exterior flame,when the wind speed is 0m/s,the evolution of the exterior flame is the fastest,and increasing the wind speed will suppress the development of the fire;If the wind speed exceeds 3m/s,the overflow fire is difficult to ignite the superstructure.If the wind speed is lower than 3m/s,it will usually lead to vertical multi fire source flame fusion.When the fire source flame fusion occurs,the temperature rise within the unit time is shown as three fire sources>two fire sources>four fire sources.When the three fire sources flame fusion occurs,the continuous combustion zone of the flame at 0m/s is vertical three layers.(5)Analyzed the evolution behavior of facade flames under 4 types of row spacing and 5 wind environment combinations,and found that the smaller the building row spacing,the weaker the leeward vortex effect in the area,and the larger the building row spacing.The leeward vortex effect is more significant in changing the direction of facade flame propagation,enhancing air flow,and cooling the smoke layer.Based on the changes in parameters such as the fusion number of fire sources,flame length,and fusion flame temperature per unit time,it was found that a parallel building with a row spacing of 1.5W is most unfavorable for the evolution of external facade flames under the influence of environmental wind in the building cluster,while a row spacing of1.0W is more conducive to fire safety from the perspective of building fire prevention.