發(fā)布時間：2018-04-14 04:26

  本文選題：地表火蔓延 + 線形火前沿�。� 參考：《中國科學(xué)技術(shù)大學(xué)》2014年博士論文

【摘要】：地表火蔓延是野火最主要的火災(zāi)形式,而外界風(fēng)速、燃料含水率和地形坡度是影響火蔓延的重要因素。前人工作中,對坡度作用的研究仍不夠充分,對坡度影響火蔓延的物理機(jī)制的認(rèn)識尚不深入。本文在燃燒風(fēng)洞中使用草原植被燃料(呼倫貝爾草原)開展不同風(fēng)速(0-5.5m/s)和含水率(4%-32%)條件下的火蔓延實(shí)驗(yàn)；基于坡度可調(diào)火蔓延燃燒平臺,重點(diǎn)開展松針(樟子松Pinus sylvestris,吉林省吉林市)燃料床上線形上坡(0°-32°)火蔓延實(shí)驗(yàn)。兩種實(shí)驗(yàn)中通過布設(shè)多根K型熱電偶觀測火蔓延速率(Rate of fire spread,簡寫為ROS))；另外在上坡火蔓延實(shí)驗(yàn)中,使用稱重板、皮托管和熱流計(jì)分別測量火蔓延過程中的燃燒特征、火焰周邊流場結(jié)構(gòu)以及火前傳熱特征。 從熱電偶測溫曲線中提取燃料著火的特征時刻并利用線形擬合方法計(jì)算全局ROS(火前沿在蔓延穩(wěn)定階段或距離內(nèi)的整體上表征速度)；在相鄰熱電偶間距內(nèi)使用數(shù)學(xué)平均方法計(jì)算局部ROS(火前沿在蔓延過程中不同空間位置處的推進(jìn)表征速度)。全局ROS在整體表現(xiàn)出穩(wěn)定一致性,而局部ROS表現(xiàn)出圍繞全局ROS上下波動的特征,并且波動的程度隨風(fēng)速和坡度的增加而增大。分析指出室內(nèi)實(shí)驗(yàn)中燃料床的長度是制約開展穩(wěn)定火蔓延實(shí)驗(yàn)的最主要因素。 對于草原植被燃料火蔓延實(shí)驗(yàn),風(fēng)速極大促進(jìn)ROS,在4.6m/s以下ROS隨風(fēng)速線形增加；而燃料含水率對于火蔓延產(chǎn)生顯著抑制作用。根據(jù)實(shí)驗(yàn)結(jié)果,從能量分析出發(fā)建立了一個綜合考慮風(fēng)速和含水率影響的半經(jīng)驗(yàn)半物理模型,模型的計(jì)算結(jié)果與實(shí)驗(yàn)測量值吻合。 對于上坡火蔓延實(shí)驗(yàn),ROS隨坡度增加。實(shí)驗(yàn)坡度范圍被劃分為三個區(qū)間。低坡度區(qū)：0°-20°,ROS隨坡度緩慢微弱增長；中坡度區(qū)：25°-29°,ROS隨坡度明顯增大；高坡度區(qū)：30°-32°,ROS急劇增加。坡度的作用被歸納于兩個方面：坡度自身和上坡火誘導(dǎo)產(chǎn)生斜坡風(fēng)。坡度自身造成火焰與燃料床的夾角減小增強(qiáng)了火焰的輻射傳熱能力,從而導(dǎo)致ROS增加。斜坡風(fēng)造成火焰進(jìn)一步向前傾斜并促進(jìn)燃燒,造成類似外界風(fēng)的效果。其中前者在低坡度區(qū)發(fā)揮主要作用,而后者隨著坡度的增大逐漸占據(jù)主導(dǎo)地位。 斜坡風(fēng)由火焰前后溫度場的不對稱和空氣卷吸能力的差異引起,皮托管測量結(jié)果驗(yàn)證火焰后方斜坡風(fēng)的存在。上坡線形火蔓延實(shí)驗(yàn)中,與火蔓延同向的斜坡風(fēng)不能穿透火焰面,火焰前方只存在微弱的逆向(與火蔓延方向相反)卷吸氣流。隨著坡度的增大,斜坡風(fēng)增加更加迅速；解釋了低坡度下火焰面豎直而更大坡度下火焰額外傾斜的現(xiàn)象。 上坡火蔓延中不同位置的燃料失重速率存在散布性,與局部ROS的波動特征相對應(yīng)。燃燒速率隨坡度的增大而增加,與ROS具有類似的變化趨勢。有效燃燒消耗率隨坡度的增加而減小,分析認(rèn)為在模型研究中低坡度下燃料床符合“熱薄型"通用假定；而在更大坡度下燃料床表現(xiàn)出“熱厚型”特征。 輻射和總熱兩種熱流計(jì)的測量表明,在線形火蔓延的預(yù)熱階段,輻射熱占據(jù)主導(dǎo)地位,而對流冷卻同樣發(fā)揮了重要的作用,在量級上與輻射熱損相當(dāng)。在低坡度下對流表現(xiàn)為自然對流冷卻的形式,它在火前的長距離范圍內(nèi)產(chǎn)生影響；而在高坡度下則表現(xiàn)為強(qiáng)迫對流和自然對流的混合對流冷卻形式,其中強(qiáng)迫對流冷卻由火前的逆向卷吸造成并且只在火前的短距離內(nèi)發(fā)揮作用。 基于能量平衡,建立了一個考慮輻射熱、對流熱和輻射熱損的物理模型,模型中引入自然冷卻和有效燃燒消耗率。模型預(yù)測結(jié)果與實(shí)驗(yàn)測量吻合良好,準(zhǔn)確映了ROS隨坡度急劇增加的特征,較好地解決了其他模型在較大坡度下ROS預(yù)測明顯偏低的問題。
[Abstract]:Surface fire spread is the main fire form of wildfire , while the external wind speed , fuel moisture content and terrain slope are the important factors that influence the spread of fire . In the former work , the research on slope effect is not enough , and the understanding of the physical mechanism of slope influence fire spread is not deep . In this paper , the fire spread experiment under different wind speed ( 0 - 5.5m / s ) and water content ( 4 % -32 % ) is carried out in the combustion wind tunnel .
Based on the slope - adjustable fire - spread combustion platform , the fire spread experiment of the linear upslope ( 0 擄 - 32 擄 ) on the fuel bed of pine needle ( Pinus masstris , Jilin City , Jilin Province ) was mainly carried out .
In addition , in the fire spread experiment of the upslope , the combustion characteristics of the fire spread process , the structure of the flow field around the flame and the heat transfer characteristics of the fire are measured by using the weighing plate , the Pitot tube and the heat flow meter .

extracting the characteristic moment of the fuel ignition from the thermocouple temperature measurement curve and calculating the global ROS by using the linear fitting method ( the integral upper characterization speed of the fire front edge in the propagation stability phase or distance ) ;
A mathematical mean method is used to calculate the local ROS ( propelling characterization velocity at different spatial locations in the spread process ) using mathematical averaging methods within the interval of adjacent thermocouple . Global ros exhibit stable consistency in the whole , while local ROS exhibit characteristics that fluctuate up and down around the global ROS , and the extent of the fluctuations increases with increasing wind speed and slope . The analysis indicates that the length of the fuel bed in the indoor experiment is the most important factor limiting the steady fire spread experiment .

For the experiment of grassland vegetation fuel fire spread , the wind speed greatly promoted ROS , and ROS increased linearly with wind speed at 4.6m / s .
According to the experimental results , a semi - empirical semi - physical model considering the influence of wind speed and moisture content is established from the energy analysis . The results of the model are in agreement with the experimental measurements .

For uphill fire spread experiments , ROS increased with slope . The range of experimental slope was divided into three sections . Low slope area : 0 擄 -20 擄 , ROS increased slowly with slope ;
Middle slope zone : 25 擄 -29 擄 , ROS gradually increases with slope ;
High slope zone : 30 擄 -32 擄 , ROS sharply increased . The effect of slope is summed up in two aspects : slope itself and slope wind induced slope wind . The slope itself causes the angle between the flame and the fuel bed to decrease the radiant heat transfer capacity of the flame , thus leading to the increase of ROS . The slope wind causes the flame to tilt further forward and promote combustion , resulting in similar external wind effect . The former plays a major role in the low slope area , and the latter gradually occupies the dominant position with the increase of slope .

The slope wind is caused by the asymmetry of the temperature field before and after the flame and the difference of the air entrainment ability .
This paper explains the phenomenon of flame extra inclination under the vertical and larger slope of the flame surface at low slope .

The combustion rate increases with the increase of slope . The effective combustion consumption rate decreases with the increase of slope . The effective combustion consumption rate decreases with the increase of slope , and the analysis considers that the fuel bed in the model study accords with the general assumption of " thermal thin type " , and the fuel bed shows the " hot - thin type " characteristic under the larger slope .

The measurement of both the radiation and the total heat indicates that the radiant heat takes a dominant role in the pre - heating stage of the linear fire spreading , while the convection cooling also plays an important role in the magnitude of the convection cooling .
whereas under high slope , a mixed convection cooling form of forced convection and natural convection is presented in which forced convection cooling is caused by reverse entrainment before the fire and works only within a short distance before the fire .

Based on the energy balance , a physical model considering radiant heat , convection heat and radiant heat loss is established , and natural cooling and effective combustion consumption rate are introduced in the model . The results of the model are in good agreement with the experimental measurement , and the characteristics of the ROS increasing rapidly with the slope are accurately reflected , and the problem that the ROS is obviously lower in the other models under the larger slope is solved .

【學(xué)位授予單位】：中國科學(xué)技術(shù)大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：X932

【參考文獻(xiàn)】

相關(guān)期刊論文 前1條

1 路長,朱霽平,邵占杰,周建軍;峽谷地形中森林地表火蔓延實(shí)驗(yàn)研究[J];火災(zāi)科學(xué);2003年01期

，

本文編號：1747724