本文關(guān)鍵詞：半封閉與開放空間中大氣擴(kuò)散的觀測(cè)及模擬研究　出處：《蘭州大學(xué)》2017年博士論文　論文類型：學(xué)位論文

  更多相關(guān)文章： 危險(xiǎn)物質(zhì)釋放 污染物擴(kuò)散 外場(chǎng)示蹤試驗(yàn) 半封閉空間 開放空間 計(jì)算流體力學(xué)模式 WRF模式 數(shù)值模擬

【摘要】：危險(xiǎn)物質(zhì)意外(或有意)釋放形成的非傳統(tǒng)大氣環(huán)境污染事件(例如,化工廠危險(xiǎn)氣體泄漏、恐怖分子的毒氣襲擊等)往往會(huì)造成嚴(yán)重的人員傷亡和巨大的經(jīng)濟(jì)損失。然而,相比于傳統(tǒng)意義上的空氣污染,我們對(duì)這類問題的研究和關(guān)注明顯不夠。因此,本論文圍繞半封閉空間(如工業(yè)廠房、候機(jī)廳和地鐵站等)和開放空間(如城市商業(yè)區(qū)、化工廠區(qū)等)兩類不同場(chǎng)景下發(fā)生的非傳統(tǒng)大氣環(huán)境污染事件,以工業(yè)廠房和實(shí)際城市中實(shí)施的兩次外場(chǎng)示蹤試驗(yàn)作為基礎(chǔ),通過資料分析和數(shù)值模擬相結(jié)合的研究手段,揭示了兩類不同場(chǎng)景下的流場(chǎng)和湍流以及污染物擴(kuò)散特征,驗(yàn)證了計(jì)算流體動(dòng)力學(xué)(CFD)模式對(duì)工業(yè)廠房?jī)?nèi)重氣擴(kuò)散過程的模擬能力,構(gòu)建了能夠模擬城區(qū)流場(chǎng)和擴(kuò)散過程的單向耦合模式WRFFluent。研究得到的主要結(jié)論如下:(1)基于“室內(nèi)危險(xiǎn)氣體擴(kuò)散試驗(yàn)”的觀測(cè)數(shù)據(jù)揭示了工業(yè)廠房?jī)?nèi)的風(fēng)場(chǎng)、湍流和溫度層結(jié)以及示蹤物濃度的時(shí)空變化特征。結(jié)果顯示,自然通風(fēng)條件下廠房?jī)?nèi)的風(fēng)速和湍流十分微弱,而強(qiáng)制通風(fēng)能夠顯著增強(qiáng)廠房?jī)?nèi)的水平風(fēng)速和垂直速度方差以及湍流動(dòng)能。再者,白天廠房?jī)?nèi)為強(qiáng)的逆溫層結(jié)所控制,下午2:00左右逆溫強(qiáng)度(即溫度垂直遞減率)達(dá)到最大值-0.68℃/m,而且煙霧擴(kuò)散試驗(yàn)顯示這種穩(wěn)定的熱力結(jié)構(gòu)會(huì)抑制污染物的垂直混合;夜間廠房?jī)?nèi)的大氣層結(jié)為弱不穩(wěn)定。此外,自然通風(fēng)條件下重氣(SF6)的垂直分布呈現(xiàn)出明顯的分層特征,低層平均濃度約為高層的5倍,而強(qiáng)制通風(fēng)條件下低層濃度降低,垂直分布趨向均勻。對(duì)于輕氣(NH3)示蹤試驗(yàn),濃度的垂直分布主要取決于廠房?jī)?nèi)溫度層結(jié)和強(qiáng)制通風(fēng)作用的綜合效應(yīng)。(2)借助CFD模式Fluent模擬了廠房?jī)?nèi)的重氣擴(kuò)散過程,并且結(jié)合觀測(cè)的SF6濃度數(shù)據(jù)對(duì)模式的模擬性能進(jìn)行定量評(píng)估。結(jié)果表明,模擬的底層呼吸區(qū)濃度值與觀測(cè)值吻合較好,其中standard k-ω和SST k-ω模型的模擬性能最好,模擬性能評(píng)估指標(biāo)FAC2=78%(這說明有78%的濃度模擬值是位于觀測(cè)值的0.5至2倍的區(qū)間內(nèi));Realizable k-ε次之(FAC2=72%);而standard k-ε最差(FAC2=43%)。但這四個(gè)模型對(duì)廠房?jī)?nèi)呼吸區(qū)上部重氣擴(kuò)散的模擬效果都不太理想,尤其是難以準(zhǔn)確模擬濃度的劇烈波動(dòng)特征。進(jìn)一步使用驗(yàn)證的SST k-ω模型再現(xiàn)了室內(nèi)重氣擴(kuò)散的時(shí)空演變特征,模式抓住了重氣擴(kuò)散的一些主要特征。最后,數(shù)值試驗(yàn)結(jié)果顯示呼吸區(qū)平均濃度隨著通風(fēng)率的增加呈指數(shù)遞減,這也就意味著增加通風(fēng)率能夠改善呼吸區(qū)的空氣質(zhì)量。(3)利用“城市-氣象示蹤試驗(yàn)”在榆中縣城區(qū)的觀測(cè)數(shù)據(jù),分析了城區(qū)內(nèi)的風(fēng)和湍流特征、反照率和地表能量收支狀況以及污染物的時(shí)空演變過程。結(jié)果顯示,市中心城市冠層頂風(fēng)速較城市邊緣平均偏小2 m/s,而且城區(qū)內(nèi)相鄰各觀測(cè)點(diǎn)的風(fēng)速風(fēng)向也存在較大差異;城區(qū)內(nèi)湍流會(huì)隨著邊界入流風(fēng)速的增大而增強(qiáng),并且給出一些簡(jiǎn)單的參數(shù)化關(guān)系式用于估算湍流特征量;白天大氣為中等不穩(wěn)定層結(jié),而夜間則接近于中性。其次,城市下墊面地表反照率日變化呈現(xiàn)非對(duì)稱U型結(jié)構(gòu),日出日落時(shí)刻反照率較大,白天較小且接近于常數(shù)0.14。白天能量輸送以感熱為主,感熱和潛熱占凈輻射的比例分別為23%和2%。值得注意的是白天熱儲(chǔ)量占凈輻射的比例高達(dá)75%,而夜間兩者大小相當(dāng)。此外,城市冠層頂部的污染物輸送和擴(kuò)散中平流起主導(dǎo)作用,濃度高值區(qū)位于釋放源下風(fēng)方向±20°的扇形區(qū)域內(nèi),而且主導(dǎo)風(fēng)向兩側(cè)的濃度分布接近于正態(tài)分布。而地面濃度的分布明顯偏離正態(tài)分布。(4)將中尺度模式WRF與微尺度模式Fluent相結(jié)合,構(gòu)建了單向耦合的WRF-Fluent模式,并且利用該模式對(duì)榆中縣城區(qū)內(nèi)的風(fēng)場(chǎng)和污染物擴(kuò)散過程進(jìn)行精細(xì)化模擬。結(jié)果表明,考慮了隨時(shí)間變化的邊界條件和城市建筑結(jié)構(gòu)的耦合模式WRF-Fluent可以較好地刻畫復(fù)雜的城市特征流型(例如,分流、匯合、渦旋和峽谷效應(yīng)等)。而且該模式也能夠很好地捕捉到高架源排放情景下污染煙羽隨時(shí)間的總體變化特征,但模擬的濃度高值中心位置和強(qiáng)度與實(shí)測(cè)結(jié)果之間還存在一定偏差。
[Abstract]:Hazardous substances (accident or intentional) release of the formation of non conventional atmospheric pollution events (e.g., chemical hazardous gas leak, terrorist gas attacks etc.) often cause heavy casualties and huge economic losses. However, compared to the traditional sense of the air pollution, we research and attention to this kind of problem obviously not enough. Therefore, this paper focuses on the semi enclosed space (such as industrial workshop, lounge and subway stations) and open space (such as city business district, chemical plant, etc.) of two different scenarios of non conventional gas environmental pollution incidents, two field tracer test in industrial plants and in the actual city the implementation of the research methods as the basis, through the combination of data analysis and numerical simulation, reveals the flow and turbulence and pollutant diffusion characteristics of two kinds of different scenarios, to verify the computational fluid dynamics (CFD) model The ability to simulate the diffusion process of heavy gas in industry building, construction of the main research conclusion one-way coupled model WRFFluent. can simulate the flow field and the diffusion process of the city are as follows: (1) based on the "indoor hazardous gas diffusion test" data reveals the industrial plant room in the wind field, the temporal and spatial variation characteristics of turbulence and temperature node and tracer concentration. The results showed that the wind speed and turbulence in the plant under natural ventilation condition is very weak, and the forced ventilation can significantly enhance the level of wind speed in the building and the vertical velocity variance and turbulent kinetic energy. Moreover, the day workshop for strong inversion control, inversion intensity (i.e. around 2:00 p.m. the temperature lapse rate) reached the maximum value of -0.68 DEG /m, and smoke diffusion vertical mixing test showed that the thermal structure of this stability will inhibit the pollutants; the plant within the atmosphere at night For the weak unstable. In addition, the natural ventilation conditions of heavy gas (SF6) vertical distribution shows obviously stratified features, the average concentration of low layer is about 5 times higher, and the lower concentration of forced ventilation conditions decreased, vertical distribution tends to uniform. For light gas (NH3) tracer test, the comprehensive effect of vertical the concentration distribution mainly depends on the workshop temperature stratification and forced ventilation. (2) using CFD mode Fluent diffusion process of heavy gas plant were simulated and the simulation performance of combined mode SF6 concentration observation data are quantitatively evaluated. The results show that the simulation of underlying breathing zone values are in good agreement with the observed concentration the value simulation performance of standard k- and SST k-. The Omega model best index FAC2=78% to evaluate simulation performance (which means 78% of the concentration of the simulation value is 0.5 to 2 times in the range of observations within); Realizable k- e times (FAC2=72%); Standard k- (FAC2=43%) was the worst. But the simulation results of the four models of heavy gas diffusion on the upper region of plant respiration are not ideal, especially the volatility characteristics it is difficult to accurately simulate the concentration. Further use of SST k-. Model validation reproduces the dispersion of the indoor air evolution model captures the some of the main features of gas diffusion. Finally, the numerical experiment results show that the breathing zone average concentration decreased exponentially with the ventilation rate, which means that the increase of ventilation rate can improve breathing zone air quality. (3) the city meteorological observation data - Tracer Test in Yuzhong County, analyzed the wind and the turbulence characteristics in the city, spatio-temporal albedo and surface energy balance and process for pollutants. The results showed that the canopy wind speed is the center of the city edge of the city average 2 m/s, and the city The wind in the adjacent observation points are quite different; in the city of turbulence will increase with the boundary inflow wind speed, and gives some simple parametric formula for estimating turbulent features; daytime atmosphere for secondary instability stratification, and the night is close to neutral. Secondly, ground surface city the diurnal variation of albedo under present asymmetric U type structure, sunrise and sunset albedo is large, the day is small and close to the constant 0.14. daytime energy to heat, sensible heat and latent heat of the net radiation ratio were 23% and 2%. respectively. It is worth noting that the heat in the day of net radiation reserves accounted for the proportion as high as 75%, and both the size of the night. In addition, the top of the canopy and the city transportation pollutant diffusion advection plays a dominant role, the concentration of high value sector release source area is located in the downwind direction + 20 degrees, but the dominant wind direction on both sides of the The concentration distribution near the Yu Zheng normal distribution. And distribution of ground concentration significantly deviate from the normal distribution. (4) the WRF mesoscale model and micro scale model combined Fluent, built a one-way coupled WRF-Fluent model, and the model of wind field and the pollutant of Yuzhong County in the diffusion process of the elaborate simulation results. That, considering the WRF-Fluent coupled model with time dependent boundary conditions and city building structure can well describe the city characteristic complex (e.g., shunt, confluence, vortex and Canyon effect). And the model is also able to capture well to the overall features of elevated emission scenarios of pollution plume over time but, there is a certain deviation between the high values of the simulated concentration center position and intensity and the measured results.

【學(xué)位授予單位】：蘭州大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2017
【分類號(hào)】：X51

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