影响街区峡谷浓度扩散的因素

对街区峡谷内污染扩散规律的研究是城市空气质量预测的主要内容之一。应用现代流体力学数值模拟方法进行大量算例的计算和分析,研究了城市街区峡谷污染物二维扩散的规律。在分析二维街区峡谷内浓度扩散的规律时,发现对街区峡谷浓度扩散的两个影响因素,其中定量分析了湍流脉动对浓度扩散的影响,与层流时得到的浓度扩散进行了通量积分的比较;此外,定性分析了不同类型的街区峡谷对扩散的影响。     

街区污染物扩散的数值研究

对街区峡谷内交通污染扩散规律的研究是城市空气质量预测的主要内容之一。应用现代流体力学数值模拟方法进行大量算例的计算和分析,研究了城市街区峡谷污染物二维扩散的规律。包括比较各种条件下污染物的扩散浓度,考察来流风速、街区特征比例和日照等因素对扩散的影响,通过研究流场及湍流强度分析其扩散的动力学原因,为改进工程预测模式提供依据。     

复杂地形城市SO2扩散特征的模拟研究

利用中尺度气象模式RAMS和大气扩散模式HYPACT,结合甘肃省-中科院科技合作项目"兰州市大气污染及对策研究"于2000年12月在兰州市城区进行的大气污染物监测资料,通过资料分析与模拟计算,研究了兰州市冬季SO2的扩散特点。研究结果表明:大气扩散模式较好地模拟出了SO2时空分布特征,与同期监测资料的分析结果比较一致,模式模拟的SO2浓度分布的日变化与环流场的日变化紧密相关;模拟的SO2浓度的空间分布与污染源的排放方式有关,污染源的排放高度不同,造成污染的高度也不同,高架源对地面的影响比较小,而中、低架源对地面的影响比较大。     

雷州桉树人工林小集水区地形分析与静态水文学模拟

利用小集水区生态水文学模型-Topog模型对雷州半岛桉树人工林纪家示范小集水区进行了地形分析和静态水文学模拟。地形分析表明，该集水区地表较为平坦，集水区总面积为0．63km^2，夏季、冬季与春（秋）分平均太阳辐射值分别为44MJ.m^-2．d^-1、25MJ.m^-2．d^-1和34MJ.m^-2．d^-1。在考虑太阳辐射影响与不考虑太阳辐影响两种情况下进行了集水区土壤含水量指数（WI）静态模拟。设定不同的静态壤中流参数值，Topog模型模拟结果表明，静态壤中流越大，在集水区内高WI的分布范围越大，也即土壤含水量越高。在考虑太阳辐射影响的条件下，分别设置不同的土壤导水率（T）、地表阴蔽系数（Es）、平均降雨最（R）进行了模拟。模拟结果表明，WI分布依各参数的不同而变化。T越大，在集水区内的WI重新分布越快；T越小，在集水区内WI趋向于平均分布。Es越大，集水区土壤所保持的含水量越高。集水区WI随R增大而有升高趋势。     

建筑因子对城市湖泊温度效应的模拟研究——以湖南烈士公园湖泊为例

伴随着城市化进程加快,城市快速扩展、人类活动加剧引发了诸多生态环境问题,其中城市热环境问题尤为突出,而城市湖泊在改善城市小气候方面有着重要的影响。选取湖南烈士公园湖泊作为研究对象,采用定点实测与CFD(Computational Fluid Dynamics)模拟相结合的方法,重点讨论了建筑后退湖岸距离、建筑高度以及建筑间距对湖泊温度效应的影响程度。结果表明:(1)湖泊周边建筑是影响夏季湖泊降温效应的因素之一,主要原因是建筑会降低来流风速,且建筑表面对太阳辐射的吸收和反射会抵消湖泊带来的降温作用;(2)仅改变建筑后退湖岸距离,而不改变建筑高度及布局,无法扩大湖泊降温效应的影响范围;(3)随建筑高度增大,湖泊周边温度效应的消极作用越大,削弱了湖泊的降温效应,当湖南烈士公园周边400m内建筑增加1倍时,区域温度升高0.82℃;(4)湖泊周边不同的建筑布局方式会影响城市湖泊温度效应,表现为行列式周边式点状式,仅增大建筑间距会增大建筑群对周边区域的辐射影响范围,使得受建筑影响的高温区面积增大。综上,若要削弱建筑因子对城市湖泊温度效应的负面影响,需综合考虑湖区周边建筑据湖岸距离、高度、布局多个因素,才能将湖泊的降温效应发挥到最大。该研究结果对于加深湖泊在改善城市小气候方面的认识以及城市湖泊区域的规划建设具有重要参考价值。     

粉煤灰渗滤系统处理城市非点源污染物效果评估

对粉煤灰介质渗滤系统处理城市非点源污染物的效果进行了研究.吸附实验表明粉煤灰对氨氮和磷酸盐具有良好的吸附能力.渗滤系统对雨水径流污染处理采用室内小试的方式进行,在70 d内共模拟33次雨水负荷,期间渗滤装置对溶解有机碳(DOC)的平均去除率为88.1%,总氮(TN)的平均去除率为41.0%,氨氮(NH0-N)平均去除率为95.5%,总磷(TP)去除率为81.0%,符合城市非点源污染控制的实践要求.污染物去除主要以吸附过程为主,有机物、氨氮、磷的去除主要发生在渗滤柱表层的0—10 cm,硝化-反硝化主要发生在0—40 cm之间.滤层高度可以从130 cm适当减小为100 cm.吸附动力学表明粉煤灰对氨氮的吸附在3 h达到平衡,对磷酸盐的吸附平衡时间为6 h.微生物对渗滤系统的影响需要进一步研究,随着运行时间的延长,微生物效应将得以体现,污染物的去除效果可能会进一步提高.     

鄱阳湖核心流域地区城市地表形态的异质性对地表温度的影响研究

鄱阳湖是中国最大的淡水湖,其生态保护受到高度关注。以鄱阳湖流域核心地区为研究对象,基于Landsat-8 OLI遥感影像和已更新至2015年江西省地理国情普查房屋建筑矢量数据,进行城市建筑形态及地表温度(LST)的空间分布、变化特征的定量化研究,且深入分析建筑形态与LST之间的相互影响关系。此外,利用高分辨率的3D建筑物栅格数据进行天空开阔角系数(SVF)的计算。结果表明,(1)湖区整体以低层低密度、低层高密度建筑形态为主,市级地区以中层高密度建筑、高层中密度建筑为主;低层低密度、低层高密度建筑主要分布在经济发达程度一般、城镇化率较低的县乡级地区。(2)湖区2005年和2016年10月的地表温度均低于5月,且低层低密度较为松散的建筑形态是引起湖区热环境变化最主要的建筑形态,高层高密度建筑形态的所在地区地表温度较为稳定。(3)建筑高度和建筑密度与地表温度之间呈正相关性,2016年5月地表温度与建筑高度、建筑密度的相关性系数分别为0.447和0.691,10月为0.486和0.841。从相关系数可知,建筑密度对地表温度的影响程度高于建筑高度。(4)实验区在晴好天气昼间,SVF值范围为0.06~0.79,主要频率在0.2~0.5之间。5月SVF值与地表温度之间的相关性系数为0.044,不存在明显的线性相关性;10月两者之间Pearson相关性系数为0.606,相关性较高。SVF值较小的区域,建筑分布密集,阻碍大气对流,且阻挡长波辐射能量,不易于地表热辐射的扩散。地表形态的异质性会导致高低各异的地表温度及不同程度的地表温度变化,建筑高度和建筑密度要素对鄱阳湖核心流域地区地表温度具有直接的影响,且建筑密度的影响更大。     

城市高层建筑大气颗粒物污染和噪声垂直分布特征

以空气颗粒物和噪声为研究对象,利用颗粒物监测仪和噪声仪,研究了颗粒物和噪声在不同天气状况下以及垂直方向上的变化规律,结果表明,(1)在0～56m之间,TSP、PM_(10)随高度增加而减小,56～116m之间随高度增加而增大.低空中的PM_(2.5)、PM_1相差不大,而100 m以上高空中的PM_(2.5)、PM_1污染程度明显大于地面.(2)天气条件影响颗粒物污染程度.晴天和大风天颗粒物的污染相对较轻,阴天时污染最重.(3)L_(eq(A))随高度增加而增大,最高点(116 m)处的噪声比地面高约4 dB.晴朗和阴天条件下,噪声差别不大;在大风天气条件下,高层建筑顶层的噪声污染较重.     

应用GIS模拟城市大气污染物浓度分布

从点源大气污染扩散模型出发,借助GIS的栅格与数据库运算功能,结合自已设计的推算流程,对兰州市大气污染物SO2的空间分布情况进行了模拟。经检验,该方法能够较准确的反映出兰州大气污染物的空间分布特征,较应用实测值进行插值的方法简便,具有较好的应用前景。     

水培实验中不同粒径纳米TiO_2对金鱼藻种子发芽和植株生长和生理的影响

纳米二氧化钛(TiO_2-NPs)是目前应用最为广泛的纳米材料之一,在城市污水处理厂的出水、污泥以及地表水体中已均有检出,进入到天然湿地和人工湿地中的TiO_2-NPs会在湿地生物、基质、水体之间进行迁移转化和归趋。目前针对TiO_2-NPs对湿地植物金鱼藻的毒性研究很少。本文采用水培实验方法,研究了不同粒径TiO_2对金鱼藻种子发芽和植株生长的影响,解析了TiO_2-NPs对金鱼藻的生态毒理效应。研究结果表明:各粒径TiO_2-NPs对金鱼藻种子的发芽均具有一定的抑制作用,表现为发芽率、发芽幼苗重量、发芽指数、发芽势和活力指数的降低,且粒径越小、浓度越高对金鱼藻种子发芽的抑制作用越强,4 nm、20 nm和50 nm的TiO_2-NPs对金鱼藻种子发芽的半数有效浓度(EC_(50))分别为1 180、1 520和1 810 mg·L~(-1)。TiO_2-NPs对金鱼藻植株的毒害作用表现为叶片失绿发黄、脱落,植株呈萎焉状,并且TiO_2-NPs的粒径越小、浓度越高毒害作用越明显。随TiO_2-NPs浓度升高,处理后金鱼藻叶片的叶绿素含量和植株体内的Mg含量均降低,丙二醛(malondialdehyde,MDA)含量均升高,而超氧化物歧化酶(superoxide dismutase,SOD)活性则先升高后降低,而且越小粒径的TiO_2-NPs对金鱼藻的处理效果越明显。3种粒径的TiO_2-NPs均能进入金鱼藻体内,粒径越小、浓度越高进入的量越多。综上表明,TiO_2-NPs对金鱼藻种子发芽和植株生长均有一定的抑制作用,且粒径越小、浓度越高抑制作用越强。     

Estimation method to identify scalar point source in turbulent flow based on Taylor’s diffusion theory

We introduce a new approach to diffusion-source estimation for quick identification of the unknown source, based on Taylor’s diffusion theory for turbulent transport of passive scalar from a fixed point source. In order to evaluate the method, we used planar laser-induced fluorescence to measure the concentration field of fluorescent dye in water flowing in a channel. We considered two kinds of datasets: basis data and observed data. The former is used to determine the basis functions characterizing the streamwise dependence of variances for three statistics: the mean concentration, root-mean-square (RMS) of fluctuations in the concentration, and RMS of the temporal gradient of the fluctuating concentration. Consistent with Taylor’s theory, we found that the lateral distribution of each statistic was basically Gaussian, and their standard deviations increased as a function of the square root of the distance from the emitted point. Based on these facts, a basis function can be formulated and expected to be valid for estimation of unknown sources. Source estimation was performed with the observed data, which corresponded to limited available information about the concentration from an unknown point source. We confirmed a good prediction accuracy of the proposed method with an averaged bias as small as the turbulent integral scale. Better precision was achieved by employing several statistics simultaneously. In this case, the standard deviation of the estimated source position was assessed at 14 % of the mean distance between the source and measurement points, after 100 source-estimate trials with different datasets. The methodology tested in this paper is expected to be applicable more general and complex environmental diffusion issues involving anisotropic turbulent dispersion, and space–time variable mainstream systems; but its versatility in such systems is currently under investigation.     

Experimental analysis of Froude number effect on air entrainment in the hydraulic jump

A hydraulic jump is characterized by strong energy dissipation and mixing, large-scale turbulence, air entrainment, waves, and spray. Despite recent pertinent studies, the interaction between air bubbles diffusion and momentum transfer is not completely understood. The objective of this paper is to present experimental results from new measurements performed in a rectangular horizontal flume with partially developed inflow conditions. The vertical distributions of the void fraction and the air bubbles count rate were recorded for inflow Froude number Fr ₁ in the range from 5.2 to 14.3. Rapid detrainment process was observed near the jump toe, whereas the structure of the air diffusion layer was clearly observed over longer distances. These new data were compared with previous data generally collected at lower Froude numbers. The comparison demonstrated that, at a fixed distance from the jump toe, the maximum void fraction C _max increases with the increasing Fr ₁. The vertical locations of the maximum void fraction and bubble count rate were consistent with previous studies. Finally, an empirical correlation between the upper boundary of the air diffusion layer and the distance from the impingement point was derived.     

Self-aeration in the rapidly- and gradually-varying flow regions of steep smooth and stepped spillways

In high-velocity chute flows, free-surface aeration is often observed. The phenomenon is called self-aeration or white waters. When the turbulent shear stresses next to the free-surface are large enough, air bubbles are entrained throughout the entire air–water column. A rapidly-varied flow region is observed immediately downstream of the inception point of free-surface aeration. An analytical solution of the air diffusion equation is proposed and the results compare well with new experimental data. Both experiments and theory indicate that the flow bulking spans over approximately 3–4 step cavities downstream of the inception point of free-surface aeration on a stepped chute. Further downstream the void fraction distributions follow closely earlier solutions of the air diffusion equation. The application of the diffusion equation solution to prototype and laboratory data shows air bubble diffusivities typically larger than the momentum transfer coefficient. The result highlights however a marked decrease in the ratio of air bubble diffusivity to eddy viscosity with increasing Reynolds number. The finding might indicate some limitation of laboratory investigations of air bubble diffusion process in self-aerated flows and of their extrapolation to full-scale prototype applications.     

连云港市新海地区水污染集中控制系统

本文论述了连云港市新海地区水污染集中控制系统的四个主要问题：尾水最终出口，污水截流工程，污水集中处理工艺、点源治理规划。提出了的近北远南，截流沟道、河滩漫流、排口分级管理的新观点。     

RANS-based simulation of transverse turbulent mixing in a 2D geometry

Although transverse mixing is a significant process in river engineering when dealing with the discharge of pollutants from point sources or the mixing of tributary inflows, no theoretical basis exists for the prediction of its rate, which is indeed based upon the results of experimental works carried on in laboratory channels or in streams and rivers. The paper presents the preliminary results of a numerical study undertaken to simulate the transverse mixing of a steady-state point source of a tracer in a two-dimensional rectangular geometry, which is expected to reproduce a shallow flow. This geometry is that of Lau and Krishnappan (J Hydraul Div 13(HY10):1173–1189, 1977), who collected turbulent mixing data for a shallow flow. In the numerical study an approach based on the Reynolds Averaged Navier–Stokes (RANS) equations was applied, where the closure problem was solved by using turbulent viscosity concept. Particularly, the classical two-equations k–? model was used. Two methods were applied to the model results to evaluate the turbulent transverse mixing coefficient. The effect on transverse mixing of a grid located upstream the tracer source was also studied. Numerical results were generally higher than the experimental data. This overestimation could be explained considering the hypothesis of isotropic turbulence underlying the k–? model, which can lead to large turbulent viscosities and rate of mixing. However, RANS-based results may still be considered acceptable also providing the large uncertainties associated with literature predictive equations.     

Improved source,improved quality? Demand for drinking water quality in rural India

This paper tests the hypothesis that the expansion of improved drinking water supplies in rural India reduced household expenditure on water quality, offsetting some of the quality benefits from source protection. I estimate demand for in-home treatment using geological characteristics to predict a household's drinking water source. The probability of treatment and in particular boiling reduces by 18–27 percentage points in response to source protection, offsetting 4% of the water quality gains and saving households 0.5–1% in monthly expenditure. Behavioral choices partly counteract the water quality gains from source protection.     

Improved source,improved quality? Demand for drinking water quality in rural India

This paper tests the hypothesis that the expansion of improved drinking water supplies in rural India reduced household expenditure on water quality, offsetting some of the quality benefits from source protection. I estimate demand for in-home treatment using geological characteristics to predict a household's drinking water source. The probability of treatment and in particular boiling reduces by 18–27 percentage points in response to source protection, offsetting 4% of the water quality gains and saving households 0.5–1% in monthly expenditure. Behavioral choices partly counteract the water quality gains from source protection.     

城市饮用水地表水源非点源污染研究

城市水源污染，不仅是制约国民经济发展的重要因素，而且成为危害和威胁人民健康的严重社会问题在原污染得到初步控制的情况下，非点源污染已经成为水源地的重要污染源。文章在讨论水源地非点源污染来源的基础上，分析了水源地非点源污染的危害，提出了非点源污染的防治对策。