【摘要】：火旋風(fēng)是一種燃燒和周圍旋轉(zhuǎn)環(huán)量相互耦合作用而誘發(fā)的具有強(qiáng)烈旋轉(zhuǎn)的特殊火現(xiàn)象。它常見于森林、野外、森林城鎮(zhèn)交界域火災(zāi)中。與普通池火相比,火旋風(fēng)的燃燒速率,火焰高度,火焰溫度,火焰發(fā)射率和輻射熱流顯著增高。而且火旋風(fēng)自身也是一種結(jié)構(gòu)復(fù)雜的旋轉(zhuǎn)渦旋�，F(xiàn)實(shí)火災(zāi)中,火旋風(fēng)強(qiáng)烈的旋轉(zhuǎn)速度場可以抬升起周圍的任何物體并誘發(fā)飛火現(xiàn)象產(chǎn)生新的點(diǎn)火源,進(jìn)而加快火災(zāi)的蔓延。因此,研究火旋風(fēng)的燃燒和流動特性規(guī)律,有利于進(jìn)一步清楚地認(rèn)識這種特殊的自然現(xiàn)象,從而為火旋風(fēng)災(zāi)害的預(yù)防和撲救提供可靠的理論依據(jù),具有重要的基礎(chǔ)科學(xué)意義和應(yīng)用價(jià)值。 本文的研究目標(biāo)是,利用空氣射流設(shè)計(jì)并構(gòu)建一個(gè)開放環(huán)境的火旋風(fēng)實(shí)驗(yàn)平臺；研究開放環(huán)境實(shí)驗(yàn)平臺產(chǎn)生的火旋風(fēng)的燃燒速率、火焰高度和火焰溫度等燃燒動力學(xué)特性,建立這些動力學(xué)特性與火焰尺寸、熱釋放速率和外圍環(huán)量等參數(shù)的依賴關(guān)系；系統(tǒng)考察火旋風(fēng)火焰的輻射特性,包括火焰發(fā)射率、炭黑體積分?jǐn)?shù)和輻射熱流密度等,并且建立輻射預(yù)測模型；詳細(xì)研究火旋風(fēng)火焰的流場特性,包括軸向、切向和徑向速度分布等。 本文具體工作包括： 首先,建立了一個(gè)新型空氣幕式火旋風(fēng)實(shí)驗(yàn)平臺。前人用于實(shí)驗(yàn)室模擬火旋風(fēng)的裝置主要分為機(jī)械驅(qū)動式平臺和熱驅(qū)動式實(shí)驗(yàn)平臺,而且他們所用的實(shí)驗(yàn)平臺都存在外圍固壁結(jié)構(gòu),如四面墻式平臺的外圍固壁,這不利于研究火旋風(fēng)對外界物體的影響,尤其是不利于研究火焰輻射。本文利用空氣射流產(chǎn)生的空氣幕取代了原有四面墻式實(shí)驗(yàn)平臺的固壁,搭建了一個(gè)空氣幕式火旋風(fēng)平臺。詳細(xì)分析了所用空氣射流的特性,確立了空氣幕的最佳偏轉(zhuǎn)角,以產(chǎn)生穩(wěn)定的火旋風(fēng)。通過燃料質(zhì)量損失速率數(shù)據(jù)的比較,驗(yàn)證了實(shí)驗(yàn)的重復(fù)性。 其次,系統(tǒng)研究了空氣幕式平臺產(chǎn)生的火旋風(fēng)的燃燒速率、火焰高度和火焰溫度等燃燒特性,建立了各參數(shù)間的依賴關(guān)系。對燃燒速率數(shù)據(jù)的分析表明火旋風(fēng)的燃燒過程包括五個(gè)階段,其中包括維持時(shí)間很長的準(zhǔn)穩(wěn)態(tài)燃燒階段,而且燃燒速率數(shù)據(jù)可以很好地符合前人提出的燃燒速率與環(huán)量的關(guān)系模型。通過量綱分析和數(shù)據(jù)擬合,建立了火焰高度對熱釋放速率和環(huán)量這兩個(gè)物理參數(shù)的依賴關(guān)系,并定義了一個(gè)標(biāo)準(zhǔn)化高度,同時(shí)將數(shù)據(jù)與前人的火焰高度模型進(jìn)行了比較,發(fā)現(xiàn)本文獲得的火焰高度數(shù)據(jù)也可以很好地符合前人的模型�；鹦L(fēng)火焰軸向溫度分布表明其在連續(xù)火焰區(qū)、間歇火焰區(qū)和羽流區(qū)隨標(biāo)準(zhǔn)化高度的變化不同。徑向溫度分布表明火焰內(nèi)部富燃區(qū)的存在。 然后,詳細(xì)分析了火旋風(fēng)火焰的發(fā)射率和炭黑體積分?jǐn)?shù)。根據(jù)灰體假設(shè)和基爾霍夫定律,實(shí)驗(yàn)中利用紅外技術(shù)方法測量了火旋風(fēng)火焰的發(fā)射率,并且得到了一個(gè)發(fā)射率隨火焰直徑變化的半經(jīng)驗(yàn)?zāi)Ｐ蛃=1-e-3.68d�；诨鹧孑椛淅碚摴浪懔颂亢诤洼椛錃怏w的發(fā)射率,發(fā)現(xiàn)輻射氣體的發(fā)射率很小,可以忽略。通過對炭黑發(fā)射的理論分析,計(jì)算了火焰的炭黑體積分?jǐn)?shù),發(fā)現(xiàn)其隨著標(biāo)準(zhǔn)化高度先增大,而后出現(xiàn)減小的趨勢。通過與普通池火數(shù)據(jù)相比發(fā)現(xiàn),火旋風(fēng)火焰的平均熄滅系數(shù)是普通池火的4-5倍；而且火旋風(fēng)的炭黑體積分?jǐn)?shù)比池火的大,這可能是引起在相同的火焰直徑下火旋風(fēng)發(fā)射率更大的原因。 再次,建立了一個(gè)分層輻射預(yù)測模型。模型中將火焰分成多層,每層火焰被當(dāng)做是灰體,即火焰的發(fā)射是均勻的。通過計(jì)算每一層火焰向外的輻射熱流,然后將多層火焰的輻射加和求得火焰的熱流密度。實(shí)驗(yàn)中測量了火焰垂直方向和徑向方向的熱流密度分布。通過實(shí)驗(yàn)數(shù)據(jù)和模型模擬結(jié)果的對比,發(fā)現(xiàn)模型可以很好地預(yù)測火焰輻射熱流密度的分布。根據(jù)輻射熱流密度在垂直方向和徑向方向的分布,得到了火旋風(fēng)火焰的輻射分?jǐn)?shù)約為44%。 最后,借助圓柱殼體實(shí)驗(yàn)裝置研究了火旋風(fēng)火焰內(nèi)外的流場特性。利用粒子圖像測速方法(PIV)測量了火旋風(fēng)火焰內(nèi)部和外部的流場,并分析了火旋風(fēng)火焰的漂移特性。結(jié)果表明：火旋風(fēng)是一種穩(wěn)定的渦旋,其渦核內(nèi)部的流體做剛性旋轉(zhuǎn),具有恒定的角速度,其切向速度沿徑向距離線性增大,環(huán)量與徑向距離成二次方指數(shù)關(guān)系；渦核外部的流動是一個(gè)自由渦旋,其切向速度與徑向距離成反比,在此區(qū)域火焰的環(huán)量是一個(gè)恒定值�；鹦L(fēng)軸向速度在徑向方向的變化符合高斯分布,其沿徑向距離逐漸減小,在中心軸線處達(dá)到軸向速度最大值。在緊貼壁面的邊界層,徑向速度隨徑向距離先增大,然后逐漸減小。隨著高度的增加,徑向速度分布受火焰漂移的影響增大,產(chǎn)生了很大的誤差。獲得了火焰漂移引起的火焰位置在y軸的投影變化的概率密度分布,發(fā)現(xiàn)沿著徑向距離,火焰出現(xiàn)的概率逐漸減小,其概率密度分布呈現(xiàn)高斯分布特性。
[Abstract]:Fire whirlwind is a special fire phenomenon with strong rotation induced by the coupling of combustion and circumferential rotational circulation. It is common in forest, field, forest and town boundary fires. In real fires, the strong rotational velocity field of a fire whirlwind can lift up any object around it and induce a new ignition source, thus accelerating the spread of a fire. Special natural phenomena provide reliable theoretical basis for fire cyclone disaster prevention and extinguishing, and have important basic scientific significance and application value.
The aim of this paper is to design and construct an open environment fire whirlwind experimental platform by using air jet; to study the combustion kinetic characteristics of the fire whirlwind produced by the open environment experimental platform, such as combustion rate, flame height and flame temperature, and to establish these dynamic characteristics and flame size, heat release rate and peripheral circulation parameters. The radiation characteristics of fire whirlwind flame, including flame emissivity, carbon black volume fraction and radiation heat flux, are investigated systematically, and the radiation prediction model is established. The flow field characteristics of fire whirlwind flame, including axial, tangential and radial velocity distributions, are studied in detail.
The specific work of this paper includes:
Firstly, a new type of fire whirlwind experimental platform with air curtain is established. The former devices used to simulate fire whirlwind in laboratory are mainly divided into mechanical-driven platform and thermal-driven experimental platform. Moreover, the experimental platform they used has external wall-fixing structure, such as the external wall of four-wall platform, which is not conducive to the study of fire whirlwind. In this paper, the air curtain generated by air jet is used to replace the fixed wall of the original four-wall experimental platform, and an air curtain fire whirlwind platform is constructed. By comparing the data of fuel mass loss rate, the repeatability of the experiment is verified.
Secondly, the combustion rate, flame height and flame temperature of a fire whirlwind produced by an air-curtain platform are studied systematically, and the dependence of the parameters is established. The burning rate data can well fit the relationship model between burning rate and circulation proposed by predecessors. By dimensional analysis and data fitting, the dependence of flame height on the two physical parameters of heat release rate and circulation is established, and a standardized height is defined. The data is compared with the previous flame height model. It is found that the flame height data obtained in this paper are also in good agreement with previous models. The axial temperature distribution of fire whirlwind flame shows that it varies with the normalized height in the continuous flame region, intermittent flame region and plume region.
According to the grey body hypothesis and Kirchhoff's law, the emissivity of fire whirlwind flame was measured by infrared technique, and a semi-empirical model s=1-e-3.68d was obtained. The carbon was estimated based on the flame radiation theory. It is found that the emittance of black and radiated gases is very small and can be ignored. The volume fraction of carbon black in the flame is calculated by theoretical analysis of the emission of carbon black. It is found that the emittance increases at first and then decreases with the normalized height. It is 4-5 times that of ordinary pool fire, and the volume fraction of carbon black of fire whirlwind is larger than that of pool fire, which may be the reason why the fire whirlwind emittance is higher at the same flame diameter.
Thirdly, a layered radiation prediction model is established, in which the flame is divided into several layers and each layer is regarded as a grey body, i.e. the flame is uniform. The radiant heat flux of each layer is calculated, and then the radial and vertical directions of the flame are measured. By comparing the experimental data with the simulated results, it is found that the model can well predict the distribution of the radial and vertical radial heat flux, and the radial radial fraction of the flame is about 44%.
Finally, the flow field inside and outside the flame of a fire whirlwind is studied by means of a cylindrical shell. The flow field inside and outside the flame of a fire whirlwind is measured by particle image velocimetry (PIV) and the drift characteristics of the flame are analyzed. With constant angular velocity, the tangential velocity increases linearly along the radial distance, and the circulation and radial distance are exponentially quadratic; the flow outside the vortex core is a free vortex, and the tangential velocity is inversely proportional to the radial distance, and the circulation of the flame in this region is a constant value. In the boundary layer close to the wall, the radial velocity first increases with the radial distance, and then decreases gradually. With the increase of height, the radial velocity distribution is affected by the flame drift, resulting in a great error. The probability density distribution of the projection change of the flame position on the y-axis shows that the probability of the flame appearing decreases gradually along the radial distance, and the probability density distribution presents a Gaussian distribution.
【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】：2015
【分類號】：X932

【參考文獻(xiàn)】

相關(guān)期刊論文 前10條

1 陳長坤,姚斌,范維澄;建筑物內(nèi)火旋風(fēng)中心飄移的探討與研究[J];中國工程科學(xué);2003年10期

2 秦俊,廖光煊,萬玉田,范志航;火旋風(fēng)的模擬實(shí)驗(yàn)研究[J];火災(zāi)科學(xué);2002年02期

3 張孝華;孫德軍;周建軍;蔣勇;;火旋風(fēng)的三維數(shù)值模擬[J];火災(zāi)科學(xué);2005年04期

4 張林鶴;劉乃安;周建軍;路長;;豎形槽道模型中火旋風(fēng)的發(fā)生與旋轉(zhuǎn)規(guī)律研究[J];火災(zāi)科學(xué);2006年04期

5 陳璞;劉乃安;;火旋風(fēng)模擬實(shí)驗(yàn)中熱電偶測溫輻射誤差修正方法研究[J];火災(zāi)科學(xué);2009年02期

6 秦俊,廖光煊,王喜世,范志航;紅外熱成像方法測量火旋風(fēng)溫度的實(shí)驗(yàn)研究[J];激光與紅外;2002年01期

7 湯曉麗,史鐘璋;橫向氣流作用下氣幕封閉特性的理論研究[J];建筑熱能通風(fēng)空調(diào);1999年02期

8 黃松;何川;;空氣幕研究現(xiàn)狀及展望[J];建筑熱能通風(fēng)空調(diào);2008年05期

9 秦俊,廖光煊,王喜世,范志航;三維LDV測量火旋風(fēng)的實(shí)驗(yàn)研究[J];量子電子學(xué)報(bào);2002年05期

10 王剛,金希蕾;火風(fēng)現(xiàn)象的觀測研究和數(shù)值模擬[J];林業(yè)科技;2003年01期

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