Studies On Fire Development Inside Compartment And The Associated Ejected Facade Flame Behavior Under Different Ventilation Condition

With our country socialist construction and the rapid development of urbanization,high-rise buildings as a national landmark of the city,increases significantly.But also,fire accidents occurred in high-rise buildings frequently.In recent years,the high-rise building fire accidents happened,formed the flame ejecting through the opening of the compartment,further induced the large-scale catastrophic fire spread along the building facade due to strong radiation/convection,causing heavy casualties,economic loss and social impact.Thus,building facade fire safety has become an important challenging issue.The flame ejected through the opening derived from the compartment fire.Previous work mainly focused on:combustion and temperature evolution inside the compartment,the evolution of the neutral plane and the critical heat release rate for flame ejection through the opening,air entrainment behavior and characteristic parameter distribution of ejected facade fire.In addition,there are also studies on the compartment-facade fire behaviour and characteristic parameters profile for various conditions considering the realistic fire scenario,such as various fire source condition inside the compartment(fire source dimension and location),opening characteristics,horizontal eaves above the opening,building vertical wall opposite to the opening,side walls on both sides of the openings,a special environmental conditions of sub-atmospheric pressure on plateau,and the ambient environment wind effect.It's noted that previous work mainly considered the fixed(or limited)fire source location,considering the window was entirely opened hence with a complete ventilation condition.However,noted that in reality of the high-rise building fire,the location of the fire sources(burning surface,i.e.,bed,table or cabinet)can be practically at various elevations above the floor,the casement window as the traditional window design is widely used in high-rise buildings,there is still a lack of research on the flame extinction behaviour in the compartment under reduced ventilation conditions,as well as no work reporting the flame pulsation behaviour of the external venting facade fire,an inherent characteristic of the ejected facade flame,In addition,the environment wind is one of the important boundary condition for the building fire,the fire was aid by wind,will have important impact on the fire development inside compartment and the associated ejected facade flame behavior.This paper mainly investigated the fire evolution inside compartment and the associated ejected facade flame behavior under different ventilations condition,five various scale compartment fire experiments were carried,the temperature inside the compartment,the critical heat release rate for flame ejection as well as the characteristic parameter of ejected facade fire was measured.The characteristic parameter similarity analysis was developed on account of the classical theoretical models,such as the enclosure fire dynamics,length scale of the opening as well as the ejected flame characteristic parameters.While,the numerical simulation was built to visualize and analyze the flow field structure with fire dynamic simulation software(FDS),assisting in analyzing and modeling.Further,Further,the influence mechanism of fire source elevation(height,above the floor)inside the compartment,opening forms(casement window,reduced ventilation compartment)and external environment wind(external sideward wind and back-roof wind)forming various ventilation condtion on fire development inside compartment and the associated ejected facade flame behavior were revealed,theoretical characterization models were established.The specific research contents included the following five aspects:(1)The effect of fire source elevation above the floor of a compartment on the ejected facade flame behavior was studied.The evolution of the temperature inside the compartment,critical heat release rate(HRR)for flame ejection,neutral plane and the facade flame height with the various burner elevations were quantified.The critical heat release rate model coupled with the opening elevation(above the floor)and the burner elevation was established.The numerical simulation was carried to visualize the flow field,which is used to interrupt the evolution of the characteristic parameters.A new characteristic length was proposed concerning the evolutions of temperature inside compartment and the neutral plane elevation(or flame vertical thickness through the opening),which determines the buoyancy of the hot gas outflow through the opening.The measured facade flame heights at various burner elevations were shown to correlate well by the non-dimensional excess heat release rate as well as the new characteristic length.(2)Fire development inside compartment and the associated ejected facade flame behavior with a casement window of various opening angles were studied.It is found that the upper-part gas temperature inside the compartment increases,while the critical heat release rate for flame ejection as well as the external facade flame height decreases,with increasing of the window opening angle as it is less than 60 degrees.Then,all these quantities change little as the window opening angle it is higher than 60 degrees.A new effective window ventilation factor characterized various window opening angle as well as the opening dimension was proposed to describe the evolutions of these quantities.(3)The transient flame extinction behavior with fuel diffusion combustion inside a wall-opening compartments at reduced ventilation condition was studied.It is found that flame extinction is easier to occur for smaller opening size or relatively larger compartment scale,which could be well represented by two non-dimensional quantities,i.e.,the GER and non-dimensional heat loss;The evolution of the the time to reach flame extinction and the gas temperature inside the compartment when flame extinction is reached was revealed,A formula is established to describe the critical gas temperature right before extinction as a function of a newly defined non-dimensional integrated parameter including both fuel combustion heat release and heat loss factors,in which the fuel supply rate,opening ventilation,compartment scale and transient extinction time scale are involved in general to reflect physically their interplay in controlling the flame extinction inside the compartment.(4)The flame pulsation magnitude and flame pulsation frequency of the ejected facade flame from opening of a compartment was studied.The maximum-mean-and continuous flame height as well as the flame pulsation amplitude of the ejected facade flame was quantified,which shows all increases with the heat release rate.The ratio of maximum flame height to the mean flame height was about 1.30,while the ratio of mean flame height to continuous flame height was about 1.60;both of them were independent of opening geometries and heat release rates.The measured flame pulsation frequency of the ejected facade flame showed to be much lower than the predicted values by previous classic models developed for free buoyant diffusion flames,which is due to physically the inherent special exit condition(with initial horizontal convection flow of heat)at the opening for the ejected facade flame.A new formula was proposed for the flame pulsation frequency of the ejected facade flame in terms of a non-dimensional function between Strouhal number(St)and Froude number(Fr),using as the characteristic flame uprising velocity and opening characteristic length scale as the characteristic length of the source exit convection flow condition at the opening.The flame pulsation frequency showed to be well represented by the proposed formula.(5)The temperature evolution and the transiton inside a fire compartment as well as ejected facade flame;characterisc morphologic paramter from the opening of compartment fire with external sideward wind were studied.The new phenomenon of the temperature transition from the leeward to the windward was found,which was quantified by the critical heat release rate.This transition was interpreted based on the relative strength of buoyancy to the inertial force of external sideward wind.A non-dimensional correlation was proposed to characterize the critical heat release rate as a function of a newly derived wind Froude number.In addition,the facade flame height just decreased with increase in sideward wind speed.However,the flame horizontal extending distance increased for relatively large openings,but first increased then decreased for relatively small openings,with increase in sideward wind speed in this range.A non-dimensional analysis was performed based on the physical mechanism of air entrainment change and tilting of the flame caused by external sideward wind.These facade flame quantities were shown to correlate well to two proposed non-dimensional numbers based on the analysis,i.e.,the ratio of air entrainment caused by the sideward wind to that induced by flame buoyancy itself with no wind,and the wind Froude number representing flame tilting caused by the sideward wind.(6)The ejected flame behavior from an opening of a compartment under horizontal ambient back wind,passing over the roof(back roof-wind)was studied by experimental work and similarity analysis.Four basic flame morphologic characteristic parameters are considered:flame height,flame width,flame downwind horizontal extension distance and overall flame length,are quantified comprehensively involving various opening dimensions,heat release rates and wind speeds.It's found that the flame morphologic characteristics all vary little at relatively lower wind speeds.With further increasing wind speed,the flame height decreases,while the flame width and the flame downwind horizontal extension distance increase monotonically,resulting in a complex evolution of overall flame length.Non-dimensional similarity analyses are performed based on the combined physical mechanisms of tilting of the flame,the change in air entrainment/mixing caused by ambient back roof-wind for the flame body above the roof,as well as the competition of the horizontal momentum of the outflow at the opening and the buoyancy induced upward flow by the flame itself.Basic formulae are proposed,based on the derived non-dimensional quantities,to describe these flame morphologic characteristics systematically.