油污染全场模拟的湍浮力流动k-ε模型

以通用的k-ε湍流模型为基础,针对油—水两相流动体系的特点,提出了油污染全场模拟的湍浮力流动k-ε模型.模型不仅在控制方程中计及了密度变化,而且在控制方程中加进了浮力项,并对湍流Schmidt数也作了浮力修正.从而计及了浮力对紊动的影响.结果表明,模型的模拟效果非常满意.     

Numerical simulation of stratified turbulent two phase flow in aquatic environment

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Large-eddy simulation of a turbulent reacting plume

The results of large-eddy simulations (LES) of a chemically reacting, dispersing plume in a turbulent boundary layer are presented. The detailed simulations of the dispersion mechanisms are used to investigate the effects of turbulent fluctuations on nonlinear chemical reactions. The idealized single reaction between ozone and nitrogen oxides, NO+O₃→NO₂+O₂, is used as a representative simple, irreversible binary reaction. Effects of different reaction rates are investigated by varying the source NO concentration, while maintaining a constant ambient ozone level. The simulations demonstrate that the rate of production of NO₂ is significantly affected by the turbulent nature of the dispersing plume. The effect of incomplete turbulent mixing of the two reactants on the reaction rate can persist for long distances downstream, particularly for the high NO levels typical of power plant stacks. The LES results also show that the important measure of the turbulent fluctuations, the turbulence segregation coefficient, may be reasonably approximated by a constant value over most of the plume cross-section. This result may prove useful for simplified plume modeling, but will depend on whether the range of constant segregation coefficient covers the whole reaction region since this takes place predominantly in the plumeedges.     

雨滴表面惯性粒子捕集的湍流效应数值分析

雨滴对气溶胶粒子的清除系数与捕集效率密切相关,并依赖于雨滴附近的气流型式.考虑到实际大气背景均为湍流状态,分别对层流和湍流状态下大尺寸雨滴表面上惯性粒子的捕集过程进行了数值模拟,讨论了湍流脉动对不同粒子轨迹的畸变和扰动.结果表明,层流条件下的模拟结果与已有的实验结果具有很好的一致性.若对雨滴的绕流附加一个湍流强度,则雨滴附近流动速度的随机变化将对粒子的运动轨迹产生明显的影响,导致惯性粒子在湍流状态下被雨滴捕获的效率大于层流捕集效率,湍流脉动效应对粒子捕集效率的提高幅度随粒子尺度的增大而减弱.     

生命周期评价概述

文章阐述了生命周期评价的基本概念以及评价的基本框架过程。生命周期评价包含３个部分：清单分析，影响评价和改进措施分析，文章对这３个方面从内容到结果分别详细作了论述。     

On vortex loops and filaments: three examples of numerical predictions of flows containing vortices

Vortex motion plays a dominant role in many flow problems. This article aims at demonstrating some of the characteristic features of vortices with the aid of numerical solutions of the governing equations of fluid mechanics, the Navier-Stokes equations. Their discretized forms will first be reviewed briefly. Thereafter three problems of fluid flow involving vortex loops and filaments are discussed. In the first, the time-dependent motion and the mutual interaction of two colliding vortex rings are discussed, predicted in good agreement with experimental observations. The second example shows how vortex rings are generated, move, and interact with each other during the suction stroke in the cylinder of an automotive engine. The numerical results, validated with experimental data, suggest that vortex rings can be used to influence the spreading of the fuel droplets prior to ignition and reduce the fuel consumption. In the third example, it is shown that vortices can also occur in aerodynamic flows over delta wings at angle of attack as well as pipe flows: of particular interest for technical applications of these flows is the situation in which the vortex cores are destroyed, usually referred to as vortex breakdown or bursting. Although reliable breakdown criteria could not be established as yet, the numerical predictions obtained so far are found to agree well with the few experimental data available in the recent literature.     

Overall efficiency of tubular inlets sampling at 0–90 degrees from horizontal aerosol flows

We have developed a unified and comprehensive model for the overall efficiency of tubular inlets sampling from horizontal aerosol flows at 0–90° relative to the wind direction. In our model, derived from experimental data obtained in our wind tunnel, the transmission efficiency is separated into two components: one due to gravitational settling in the boundary layer and the other due to impaction. The gravitational settling component is determined by extending our previously developed isoaxial sampling model to nonisoaxial sampling. The impaction component is determined by a new model that quantifies the particle losses caused by direct wall impaction. The model also quantifies the additional particle losses resulting from the turbulent motion in the vena contracta which is formed in the inlet when the inlet velocity is higher than the wind velocity.The equation for the gravitational settling component considers the inertial behaviour of the particles by including the Stokes number, the flow development in the boundary layer by including the Reynolds number and the gravitational settling in the boundary layer by including a modified gravitational settling parameter. The equation for the impaction component considers direct wall impaction and the losses due to vena contracta formation through the Stokes number, velocity ration and sampling angle. Direct wall impaction is further differentiated by the gravity effect on the impaction process which distinguishes upward from downward sampling. Our equations for transmission efficiency in combination with aspiration efficiency equations determine the overall efficiency of tubular, sharp-edged inlets at all orientations of the inlet relative to horizontal aerosol flows.     

水环境两相分层流数值模拟

以研究水环境两相分层流精细预报模型为目标,广泛地涉及了两相湍流精细模拟的理论和方法。用Eulerian坐标系中多流体模型统一描述两相各自的运动,并分别对两相本分的湍流输运观作以及地相间互作规律进计模拟,建立了水环境两相分层流的双流体模型对包含有浮力和密度分层的两相湍流进行了数值模拟,计算结正确地反映了分层及紊动特征,与实测结果吻合较好     

Agglomeration and removal characteristics of fine particles from coal combustion under different turbulent flow fields

Turbulent agglomeration is a promising pretreatment technology for improving the removal of fine particles in industrial flue gas, which can improve the particle removal effect of dust removal equipment safely and economically. However, due to the complexity of turbulence mechanisms, the relationship between turbulent flow fields and the agglomeration of fine particles is not known with precision, resulting a weak promotion effect for particle removal with this pretreatment technology. In this work, three kinds of turbulent agglomerators were constructed to investigate the agglomeration and removal characteristics of fine particles under different turbulent flow fields. The results demonstrated that the turbulent agglomerator with small-scale and three-dimensional vortexes in the flow field had the best effect in improving the agglomeration and removal of fine particles. Two kinds of agglomeration modes in turbulent agglomeration were proposed, one being agglomeration between fine particles in the vortex area, and the other the capture of fine particles by coarse particles. Furthermore, the motion trajectory, relative velocity and residence time of fine particles of different sizes in different flow fields were calculated by numerical simulation to investigate the interaction mechanism of particle agglomeration and turbulent flow fields. The results showed that a flow field with small-scale and three-dimensional vortexes can reduce the Stokes number (St_K) and the relative velocity of particles of different sizes, and extend their residence time in a turbulent flow field, so as to obtain a better agglomeration effect for fine particles.     

紊动水体大气复氧系数研究进展

简述了影响水体中溶解氧浓度的大气复氧速率的主要因素，系统分析了自１９２４年以来国内外对紊动水体复氧系数的理论和实验和发展过程及其研究成果，对其中存在问题进行了分析探讨，认为目前众多的复氧理论和公式大多不能直接用于天然河流，要通过复氧实验确定复氧系数，并对今后这一领域的研究进行了展望。     

可降解塑料的开发与应用

以可降解塑料替代普通塑料作包装材料和农用薄膜,已成为发展的方向和趋势。本文比较详细地介绍了国内外对可降解塑料的研制现状和应用前景,并指出了可降解塑料在开发和应用方面所存在的一些问题。     

浓缩型入口下排气旋风分离器流场和性能的数值计算

运用CFD方法,对浓缩型入口下排气旋风分离器内的气固两相流动进行了研究。计算中气相采用RNGk-ε湍流模型,颗粒相采用拉格朗日坐标系下的离散相模型。重点计算了分离器流场、分离效率及其阻力特性,结果表明,采用浓缩入口后分离器内流场发生明显改变,分离器上部切向速度明显提高,有利于大颗粒的分离。同时通过对不同浓缩结构旋风分离器的分离效率和阻力特性进行分析比较,为工程设计提供了依据。     

经济系统物质流分析研究述评

经济系统物质流分析方法近年来在可持续发展研究领域发展尤为迅速。论文对该研究方法的发展历程、主要观点、逻辑框架及相关应用研究进行了评介,并在此基础上指出了其方法的主要作用和局限,对其未来研究的发展方向提出了建议:①主要作用有二,一是能够得到简洁的可持续发展示踪指标,二是得到的采用物理量为单位的物质流指标便于比较;②主要局限有三,一是大的物质流会冲淡物质流指标描述物质流动状况的清晰度,二是物质流指标与物质流动环境影响之间的联系不够紧密,三是使用范围有限制;③未来研究发展方向有三,一是挖掘物质流分析结果所蕴含的社会研究价值,二是与土地利用分析的结合,三是向物质投入产出表的迈进。     

An assessment of greenhouse gas emissions and material flows caused by the Finnish economy using the ENVIMAT model

An environmentally extended input-output (EE-IO) analysis - environmental impacts of material flows caused by the Finnish economy - was carried out in order to improve data on production and consumption in Finland. The study resulted in the ENVIMAT model, which can be used to analyze the relationship between material flows, environmental impacts and the economy. The model is based on monetary and physical input-output tables and an environmental life-cycle impact assessment. This article summarizes the main methodological aspects and findings regarding the material flows and climate impacts caused by the Finnish economy in 2002 and 2005. The Finnish model has relatively detailed input data with 150 industries and 918 products and the data on imports was assessed according to a mixed approach with the help of life-cycle inventory data. The results of the model showed that the Finnish economy uses imported material resources as much as domestic resources. Life-cycle greenhouse gas (GHG) emissions caused by imports were equivalent to 70-80% of domestic emissions. The GHG emissions embodied in imports (emissions abroad) and exports (emissions within Finland) were of the same magnitude. The analysis showed that the service sector accounted for 44% of GHG emissions caused by the domestic final use of products. Analysis of the results also showed that the indicator of total material requirement (TMR) should not be used for environmental impact comparisons of products and services. In the future, the aim is to use the ENVIMAT model for assessing temporal changes in the economy; for monitoring sustainable development; for planning climate change mitigation; and for identifying important factors in the economy and assessing their impacts.     

沉水植被降低水体浊度的机理研究

水体浊度的变化影响着水生态系统的健康,而沉水植被对降低水体浊度具有显著效果. 为明确沉水植物对泥沙的作用机理,以苦草为试验用草,开展室内水槽试验. 结果表明,苦草斑块降低了水流的输沙能力,根据试验资料估算,斑块区水流的输沙能力仅约为无草时的10%. 利用象限分析法分析了实测的紊动流场,解释了植物对泥沙作用的物理过程. 在苦草斑块区,植物冠顶以下区域(相对高度小于1.00)为下扫流态,紊动漩涡形成的下扫流将泥沙带入水底,而近底层的喷射流抵消了下扫流的能量,抑制下扫流对泥沙的冲击起动,并使下扫流挟带的泥沙顺利淤积;在植物冠顶以上区域除高密度(172株/m2)工况为下扫流态外,中、低密度(86、43株/m2)工况均为喷射流态,不利于泥沙沉降. 由于泥沙主要存在于下层水体,因此沉水植被有利于减小水体浊度.      

高效水解酸化废水处理技术初步研究

提出了一种高效水解酸化废水处理技术，通过水力学措施，可以实现水解酸化系统较强烈的湍流和涡旋，加速传质，从而使有机污染物的去除率显著增加，对照试验结果表明，对低浓度溶解性COD的去除率是传统方法的3倍以上。     

Deposition velocity and the collision model of atmospheric dispersion—II. Extension to cases with variable turbulent velocity scale

The collision model of turbulent dispersion has been extended to deal with situations where the turbulent velocity scale is dependent on position, which requires that the particles of the Monte Carlo simulation accelerate between collisions.The theory has been applied to an idealized vegetative canopy in order to illustrate the differences from the predictions of eddy-diffusivity (K)-theory arising from the finite decorrelation length scale associated with vertical turbulent velocity. For cases of high deposition to canopy elements, the collision-model results do deviate from K-theory results, although the differences are not practically significant.An extension to the model enables gravitational settling to be handled in a more realistic manner than in K-theory. By this means, it is found that the simple expedient of adding the settling velocity to the deposition velocity due to other processes is more closely valid than appears from K-theory results.     

The surface energy balance in Mexico City

Results of a field observation programme to investigate the surface energy balance of Mexico City, D.F., are presented. Direct measurements of net all-wave radiation and the turbulent sensible heat flux were conducted from a 28 m tower located about 4 km from the city centre. Heat storage in the urban fabric was parameterized and the turbulent latent heat flux was found by the residual in the energy balance equation. Most of the data were gathered in the dry season from February to the end of March 1985. The results from this tropical highland city resemble those from temperate cities in respect of the magnitude of the Bowen ratio and the diurnal trend in the amount of the net radiation partitioned into turbulent sensible heat. On the other hand, the role of heat storage is much larger than in the temperate case so that the partitioning of the sensible heat between turbulent and conductive transfer seems to be more nearly equal. Nevertheless evaporation appears to be an important term in both the surface water and energy balances. The nature of the energy balance may help explain some of the previously observed features of the heat island and humidity regimes of Mexico City.