Investigation Of Flame Geometry And Downstream Heat Flux Evolution Of Pool Fires Under Cross Flow And Inclined Surface

Pool fire is a common form of fire in real life scenario and a basic combustion type in fire research.Previously,lots of researches have been done regarding the influence of environmental factors on the flame geometry and heat flux of pool fires.However,limitations exist regarding following topics:(1)an integral model to describe flame geometry in both vertical and horizontal directions under cross flow.The cross flow speed of precedents' work was small compared to the pool size.It is obvious that when the cross flow is higher than a threshold value,the flame will contract and even be blown off,which indicates that the physical mechanism of the effect of relatively strong cross flow is not the same as that of relatively small cross flow;Besides,previous researches focused on vertical flame height,flame base drag and flame tilt,etc.,respectively.However,none integral model was proposed that is applicable for vertical and horizontal dimensions under wide cross flow speed range.The aforementioned topic is essential in understanding the physics for flame geometry evolution as well as practical utilization;(2)air entrainment and vertical flame height evolution of pool fires with inclined surface.The inclined surface can represent the inclined obstacle and inclined tunnel,thus determines the safety zone.And introducing cross flow will add on complexity of flame behavior.Limited researches have been done in this area;(3)local total heat flux evolution of pool fires under cross flow.The downstream local total heat flux determines the flame spread and thermal hazard to surroundings.In previous works,relatively small cross flow speed was used.And side entrainment of pools is enhanced under relatively strong cross flow,which changes the flame geometry and further local total heat flux.The present work used experiments and computer simulation to investigate the research points above.The main work includes:(1)Experimental study and physical analysis of the flame geometry under cross flows.Experiments were conducted to study the influence of pool size,heat release rate and cross flow speed on the flame geometry parameters in both vertical and horizontal directions,including vertical flame height,horizontal flame length,flame base drag and flame tilt angles.Based on flame geometry evaluation and boundary theory,the flame was divided into two regimes.An integral model was proposed based on dimensional analysis of cross flow speed,characteristic volumetric air entrainment and turbulent flame buoyancy as well as air required for stoichiometric combustion.(2)Experimental study of flame height and air entrainment of pool fires with inclined surface.The combined influence of inclined angle and cross flow on vertical flame height and air entrainment was investigated.Computer simulation was used to interpret flow field.It was revealed that the effect of inclined ground is the confinement to entrainment,which stretches the flame and introducing a negative pressure zone that makes the flame extend in horizontal direction.A characteristic inclined surface factor was obtained and further correlations for vertical flame height were proposed based on physics in still air and under cross flow,respectively.(3)Experimental study of local total heat flux evolution of pool fires under cross flow.Experiments were conducted employing various sizes of square pools with different heat release rates under relatively strong cross flow,relvealing complex local total heat flux evolution.It was found that the location of peak local total heat flux can be regarded the same as the flame base drag.Taking the counteraction of hot plume,forced convection brought by cross flow and natural convection into consideration,Richardson number and non-dimensional cross flow speed were proven proper for describing non-dimensional local total heat flux.And correlations for local total heat flux were proposed.