Experimental Study On Flame Attachment And Heat Flux Distribution Of Line-source Fires Under Slope Condition

In the process of fire spreading,it is often affected by cross flow and slope conditions,and the phenomenon of sudden accelerated fire spread occurs,which increases the difficulty of firefighting and threatens the life safety of firefighters.Cross flow and slope conditions will cause the flame to tilt downstream and adhere to the ground,causing the flame to contact the combustible material that has not been burned downstream,increasing the heat flux received by the combustible,and igniting it,further increasing the fire potential.For the study of fire under different slope conditions,most of the predecessors used a single fire source to explore the influence of different slopes on the dynamic parameters of flame combustion dynamics.In actual fire scenarios,the burning of fires on slopes is affected by cross flow,and often involves simultaneous burning of multiple fire sources.However,at present,there are few studies on the combustion behavior of flames under the coupled effects of cross flow and slope,or the combustion behavior of multiple ignition sources under slope conditions.In this paper,an experimental study on the combustion behavior of flames under the coupled action of cross flow and slope and the combustion behavior of dual fire sources on slopes is carried out by using a variable-angle test bench and propane as fuel.For the combustion behavior of the flame on slope under cross flow,the evolution of the flame morphology and the downstream heat flux distribution under the coupling action of cross flow and slope conditions are studied.The study found that the flame attachment length increases with the increase of the cross wind speed and the inclination angle of the slope,and the cross wind speed has a greater influence on the flame attachment length under small angles(0°-20°),and has little effect on large angles(30°50°).It is found that the heat flux first increases and then decreases with the increase of the downstream distance.Based on the comprehensive analysis of cross wind speed,air entrainment and plume buoyancy,the theoretical model of the flame shape on the slope under cross wind is proposed,and the heat flux distribution model is proposed based on the flame attachment length.For the combustion behavior of dual ignition sources on slopes,using dual ignition sources with symmetrical power,the evolution of the flame shape and downstream total heat flux distribution with the spacing of ignition sources and slope angle in dual ignition sources under slope conditions was studied.It is clarified that the downstream flame attachment length decreases with the increase of the burner spacing,and increases with the increase of the slope angle and heat release rate;and the non-monotone variation law of the total heat flux is found with the increase of the downstream distance.It was observed that when the slope angle gradually increased from 0° to 40°,the downstream flame showed three states,namely,tilting upstream,maintaining vertical,and tilting downstream.On the basis of the flame attachment length model of a single ignition source on the slope,a prediction model for the downstream flame attachment length of the slope dual ignition source was established,and combined with the downstream flame attachment length and slope angle,the downstream total heat flux distribution model was proposed.