考虑环境湍流作用的烟气上升路径方程

本文利用我国的观测资料对中性层结时的烟气拾升路径作了细致的分析。发现抬升高度与距离之间符合幂次关系,但与不考虑环境湍流作用的2/3次律有系统偏离;这一偏离与烟流半径和高度的非线性关系相一致。上述事实与国外的一些观测结果均表明,环境湍流对烟气抬升的累积作用不容忽视。为此,提出了环境湍流与自生湍流的联合作用模式,由此导得的抬升路径方程可以满意地解释上述观测事实。模式还显示,卷挟速度除取决于切变速度及湍流强度以外,还是烟流半径的函数,因而在物理上更加合理。由联合作用模式导出的终极抬升公式比不考虑环境湍流累积作用的公式更符合观测结果。     

环境湍流影响烟云抬升的比较研究

对几种烟云抬升模式进行了比较,分析了中性层结下环境湍流的对烟云抬升的作用,认为环境流连续作用于烟云抬升的各个阶段,且随烟云抬升而变化。抬升高度与环境湍流有关,湍流强度越大,抬升越低。     

若干烟云抬升公式的对比分析

本文根据南京大厂地区大气污染源资料和现场实测气象资料,对国内外常用的一些烟云抬升公式计算了各种气象条件组合下的抬升高度。并与部分实测烟云资料进行对比分析。结果表明:近几年流行的布里格斯(Briggs,G.A.)公式有过高估计,霍兰德(Holland,J.Z.)公式、莫塞斯(Moses,H.)公式、康凯夫(CONCAWE)公式和卢卡斯(Lucass,D.N.)公式的计算值与实测值相比都存在着不同程度的偏离,致使应用时受到一定的限制。1984年由建环部给出的GB式除稳定度D类外,计算的烟云抬升高度比较符合实际。     

论环境湍流对烟气抬升的作用

考虑环境湍流对烟气抬升具有增强烟气夹卷和促进烟气与环境空气间动、热量交换的双重作用，导出了中性层结条件下热烟气浮升的轨迹方程，并且无需对抬升的截止作任何假设，导得了理论的终极抬升公式。经与国内外烟气抬升实测资料对比，发现这些结果与实况基本一致。     

南京大厂区大气污染物的浓度分布

根据实测的气象资料和大气扩散参数,选用了一系列大气扩散模式和烟云抬升公式,计算了扬子乙烯工程投产后大厂地区二氧化硫等污染物的浓度场。本结果为该区的大气污染控制和城镇规划提供了依据。     

对流冷池对黑风暴沙尘抬升和传输影响的大涡模拟研究

利用"西北干旱区陆-气相互作用野外观测实验"加密观测期间敦煌站的温度探空廓线作为大涡模式的初始场,通过在模式中设置冷源的方法,模拟研究对流冷池中的湍流结构特征,以及冷池头部和尾部的湍流对沙尘抬升和垂直传输的影响;进一步通过改变冷源冷却率和冷源半径大小的敏感性试验,探究冷源强度和尺度变化对对流冷池内湍流结构、冷池移动速度和沙尘抬升效率等特征的影响。研究表明:(1)模式模拟的对流冷池结构特征与观测结果较为一致,冷池的头部为较大的湍流涡旋,尾部是受头部下沉气流的阻挡和风切变共同作用形成的湍流涡旋,强度和尺度较小,且距离头部越远,尾部湍流强度也越弱。(2)冷池头部涡旋引起的沙尘抬升潜势较尾部的大,冷池密度流抬升的沙尘大部分在冷池内混合,仅少部分扩散到冷池外,头部的沙尘绝对浓度约是尾部的两倍。(3)增大模式冷源冷却率和冷源尺度,冷池密度流强度增强,头部涡旋移动速度增大,产生的沙尘抬升潜势也增大,沙尘可被冷池内增强的湍流涡旋传输到较高的高度,但由于冷池与环境大气的夹卷作用也增强,冷池消散也较快。     

边界层大气环境与空气污染问题的风洞流体模拟实验

在大气环境风洞中,采用人工形成边界层的方法,建立一定厚度的模拟边界层,测试确定边界层特征量,如粗糙度长z。风廓线指数n等。实验揭示了形成大气边界层的物理机制。用烟云照相法对模拟形成的高架点源排放烟流的抬升高度相大气扩散参数作了实验测定,并采用波动烟流法进行数据处理。讨论了排烟速度Vs和环境风速u对烟气动力抬升的影响;此外还对阶跃下垫面条件和障碍物后旋涡区中的扩散进行了分析。     

高阶矩模式模拟对流边界层的可行性研究

本文建立了二阶矩闭合的大气边界层数值模式,并模拟了Wangara资料第33天09:00—18:00时对流边界层的发展过程。计算结果与实测资料比较吻合,同时利用该模式研究了高阶矩模式模拟对流边界层的可行性,结果指出:二阶矩方程中的湍流扩散项对模拟对流边界层内的挟卷和反梯度现象起主要作用。而局地时间变化项仅影响对流边界层内的边界湍流扩散项。因此,假如处理好二阶矩方程中的湍流扩散项,高阶矩模式和大涡模式一样可以很好地模拟对流边界层的发生、发展。     

大气湍流场中温度场结构的基本问题

本文在考虑湍流能量耗散率和温度不均匀性平滑率是变量的基础上,得到了大气湍流场中新的温度结构函数公式,它比“2/3”定律多一个修正因子[1+M_1~2(r)]~(2/9)。应用湍流能量耗散率谱的观测资料对修正因子作了估计。     

稳定大气中烟流抬升高度的确定

本文通过Boussinesq近似的非线性动力方程组,得到了烟流抬升高度的解析表达式,讨论了地形、大气稳定度等物理因子对烟流抬升高度的影响。结果表明:地形的分布对烟流抬升高度的确定有一定影响,大气稳定度对高度的影响尤为明显。本文还讨论了理论公式的实用条件。     

考虑动量和浮力通量耗散的烟气抬升解析模式

环流湍流对烟流抬升有重要的作用。本文考虑了环境湍流引起的烟流的动量和浮力通量耗散，导出了烟流抬升的控制方程，给出了烟流的轨迹方程和中性条件下热浮力烟流的终极抬升高度。在烟囱附近，轨迹方程接近2/3次律；当下风距离增大时，与2/3次律有明显偏离并逐渐变平。与外场试验资料的比较表明，本模式能较好地模拟浮力烟流的轨迹和终极高度。     

On the dispersion parameters of plumes from tall stacks in a shoreline environment

Experimental data for buoyant plumes released from high sources into layers having little ambient turbulence show that plume dispersion parameters vary in a manner similar to that during initial plume rise. This is consistent with general plume rise theory. Dispersion of plumes from tall stacks in a shoreline environment where a thermal internal boundary layer is formed often demonstrates this behaviour.     

Fluctuations of line integrated concentrations across plume diffusion in grid generated turbulence and in shear flows

The fluctuations of the instantaneous values of line integrated concentrations across plumes from point sources diffusing in turbulent shear flows, and in grid generated turbulence, have been studied experimentally using a fast response system which measured the attenuation of the intensity of an infrared beam crossing the plume. Analysis of the measurements show that the dimensionless statistical properties of the fluctuations at different distances from the source at each flow are approximately similar, in the sense that they depend primarily on the relative off-center location of the line of integration and almost independent of the distance from the source and the nature of the turbulence in the flows, as long as the characteristic length of the mean plume is not large compared to the size of the large eddies. The characteristic time of the fluctuations, on the other hand, was found to grow with the distance from the source and the autocorrelations of the fluctuations, particularly in the case of a plume diffusing in grid generated turbulence, were it found to be proportional to the lateral size of the mean plume. A—5/3 decay law of the power spectrum of the fluctuations was observed in the low frequency range which corresponds to the scale of the large eddies. The decay of the fluctuations caused by smaller eddies was much faster, as expected.     

THE RISE MODEL OF BUOYANT PLUME LIMITED BY MECHANICAL TURBULENCE

This paper has investigated the rise of bent-over buoyant plume in neutral condition.By means of the combined-effect model proposed at earlier time,authors have deduced a formula of final rise limited by mechanical turbulence and therefore have concluded that the corresponding formula neglecting the accumulated effect of ambient turbulence is only its particular case.By analyzing the function relation of the various affecting factors with the plume rise in the existing equations,it is proved that the formula derived from the combined-effect model is the most reasonable and shows more conformity to the observations.     

Experimental observations of a bifurcated buoyant plume

During measurement of the plume rise from the 381-m International Nickel Company stack (in the Sudbury area), it was observed that on some occasions the plume bifurcated. The bifurcation lasted for periods ranging from a few seconds to tens of minutes. During this time, the plume behaved like two separate plumes, each attached to the chimney, with a relatively clear region between the two plumes. The two branches travelled downwind at either the same or different heights, depending on the ambient meteorological conditions. Vertical wind direction shear tended to diffuse the two branches at different rates.In an attempt to explain the initiation and the mechanism of bifurcation, field observations are presented and analyzed.     

The effects of mesoscale turbulence on plume rise in a land/lake environment

An extensive data base of LIDAR and photographically measured plumes from the Nanticoke thermal generating station (located on the north shore of Lake Erie) has been accumulated over several years of full-scale atmospheric experiments. Analysis of the data shows that the empirical entrainment constant used in the Briggs simple plume rise formulation has a value of 0.8, which is significantly larger than 0.6 found by Briggs (1975). A hypothesis is proposed that mesoscale eddies present in the land/lake environment are responsible for vertical plume meander leading to the observed enhanced vertical plume spread and lower mean plume rise at this site. This is substantiated through theoretical considerations and experimental data. The results are significant in the computation of ground-level concentrations at such complex terrain sites.     

Study on conventional atmospheric dispersion models in china, america and canada

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A Similarity Model for Maximum Ground-Level Concentration in a Freely Convective Atmospheric Boundary Layer

A model of buoyancy- and momentum-driven industrial plumes in a freely convective boundary layer is proposed. The development combines the Lagrangian similarity models of Yaglom for non-buoyant releases in the convective surface layer with the Scorer similarity model for industrial plumes. Constraints on the validity of the extension of Yaglom’s model to the entire convective planetary boundary layer, arrived at by consideration of Batchelor’s formulation for diffusion in an inertial subrange, are often met in practice. The resulting formulation applies to an interval of time in which the entrainment of the atmosphere by the plume is balanced by the entrainment of the plume by the atmosphere. It is argued that during this interval, both maximum plume rise and ground contact are achieved. Further examination of the physical interrelationship with the Csanady-Briggs formulation serves to consolidate the model hypotheses, as well as to simplify the derivation of maximum ground-level concentrations. Experimental evidence is presented for the validity of the model, based on Moore’s published data.