Study On The Rotating Flow And Combustion Characteristics Of Multi-pool Fire Whirl In Side Slit Vertical Channel

Fire whirl is a special phenomenon in forest fire and urban fire.It is more destructive because of its faster combustion rate and larger radiation output.In the mass fire,the phenomenon of multi-source flame fusion may also be formed.Once the multi-source fire whirl is formed,it will pose a great threat to personal safety and property.However,due to the interaction between multi-source fire whirl,their physical mechanism and dynamic behavior are more complicated.Therefore,the study on the combustion behavior of multi-source fire cyclone and the deep understanding of its dynamic behavior from the physical aspects are conducive to the prevention,early control and fighting of urban and forest fires,so as to protect the safety of personnel and property.In this paper,theoretical analysis,experimental research and numerical calculation are combined to obtain the basic data of the fluid velocity field,mass combustion rate,flame height and temperature field of the multiple pool fire whirl.Then,the theoretical model of velocity distribution,mass combustion rate and flame height of multiple pool fire whirl fluid is deduced and corrected,and verified by experiment or numerical simulation.The main content includes the following three aspects:1.The flow characteristics of multiple pool fire whirl under stable state were analyzed.According to the characteristics of fire whirl,the multiple pool fire whirl are divided into three zones in the horizontal direction,namely the inner zone,the transition zone and the outer zone.The expressions of axial velocity distributions in the inner zone,the transition zone and the outer zone are derived through the assumptions.Then,by solving the helical equation of the center of fire whirl flame,the expression of axial velocity distribution of multiple pool fire whirl flame is corrected.Finally,it is verified by experiment and numerical simulation.2.It is found that thermal radiation is the main factor affecting the fuel combustion rate of multi-pool multiple pool fire whirl under stable condition.According to the flame shape in the stable state of multi-pool fire whirl,the radiation model of multi-pool fire whirl is obtained.Then,by calculating all the thermal radiation of each pool,The ratio of heat feedback and heat release rate of all pools in multiple pool fire whirl is defined as the correction factor of mass combustion rate by heat radiation.The mass burning rate of single pool fire whirl was modified to make it suitable for multi-pool fire whirl.The formula is in good agreement with experimental data and numerical simulation results.3、It is found that the fuel mass loss rate and radial velocity are the main factors affecting the flame height of multiple pool fire whirl.According to the flame shape in the stable state of multi-pool fire whirl,the flame shape model of multi-pool fire whirl is simplified.Combined with the velocity field model of multiple pool fire whirl,the relationship between multiple pool fire whirl and fuel mass loss rate and axial velocity is derived.Finally,it is verified by experiment and numerical simulation.