共查询到19条相似文献，搜索用时 187 毫秒
1.
一个对流边界层中的随机扩散模式 总被引：1，自引：0，他引：1
通过对对流边界层(CBL)湍流结构的分析,首次提出用两种不同尺度的湍流模拟CBL中的铅直扩散.在此基础上发展了一个随机扩散模式,并用它模拟了典型对流条件下两种高架连续点源的扩散.与Willis水槽模拟和Lamb等人数值模拟以及CONDORS计划外场试验的结果的比较表明,本模式能成功地模拟CBL中的横向积分浓度.与其它数值模式相比,还具有输入参数少、计算量极小和更加简单实用的优点. 相似文献
2.
本文根据宁波北仑地区的大气扩散试验研究,分别提出了适合本地区高架源扩散模式和低矮源或地面源扩散模式使用的大气湍流扩散参数。为该地区的大气环境影响评价及大气环境质量总量控制的数学模型的建立提供了实用参数。 相似文献
3.
一个预测沿岸陆中熏烟扩散的随机游动模式 总被引：1，自引：1，他引：1
本文建立了一个对流边界层中的随机游动扩散模式，并用ＫＮＲＣ试验Ｎｏ：６４的资料作了难，然后考虑混合层顶不规则夹卷界面的作用，应用于楠克沿岸陆上熏烟扩散问题，将模拟的地面轴线浓度与观测资料以及三个烟扩散预测模式的结果作了比较，结果表明：模式的模拟效能良好，所有数值计算均可在微机上实现，便于推广应用，更具实用性。 相似文献
4.
对流边界层（ＣＢＬ）中的污染扩散是非高斯型的。本文在下列三个假设下建立了双高斯型几率分布函数（ＰＤＦ）模式：１．对流边界层任一确定高度铅直速度Ｗ的几率分布函数ｐｗ由两个高斯分布迭加而成；２．从污染源释放的粒子具有源高的铅直速度几率分布，且其轨迹是线性的；３．粒子在地面的反射为全反射，在混合层高度Ｚｉ为全反射或有部分吸收。然后分析了三个高度上铅直速度Ｗ的一些统计特征量，比较了由ＰＤＦ模式计算的横风向积分浓度和Ｌａｍｂ的数值模拟［１－３］，Ｄｅａｒｄｏｒｆｆ的水槽模拟［４－６］结果，并用美国ＣＯＮＤＯＲＳ计划的外场试验资料［７］对ＰＤＦ模式进行了验证，结果均相当一致。 相似文献
5.
海岸地区空气污染物输送与扩散的数值模拟 总被引：3，自引：0，他引：3
本文建立了求解三维扩散方程的数值模式,以经过处理地形影响经连续方程调整模式计算得到的三维风场和实测铅直湍流扩散系数作为输入,模拟了沿海城市秦皇岛地区海陆风演变过程中空气污染物(SO_2)浓度的时空分布(x-y和y-z两个剖面)。模式的数值求解,在水平方向采用伪谱方法,铅直方向采用上游格式和六点格式,对三维扩散方程运用分步求解的数值方法,用计算所得的地面SO_2浓度分布和实测值比较,一致性相当好。显示在早晨和傍晚出现极大值,午后出现极小值。计算所得的日平均浓度与实测结果相比,也相当吻合。分析表明,本文所建模式行之有效,且数值计算稳定性表现良好。 相似文献
6.
城市热岛效应对污染物扩散规律影响的数值模拟 总被引：5，自引：1，他引：5
用一个二维非定常扩散方程模拟了夜间城市边界层中三种不同有效高度(20m,72m和110m)连续线源所产生的污染物浓度分布特征。数值试验结果表明:不管是否出现热岛环流,城市热岛效应使高架源产生的地面浓度增大,而使近地面源所产生的地面浓度减小。这是因为城市下垫面的热力和动力作用改变了一般的边界层低层的温度结构和湍流结构所致。 相似文献
7.
利用本溪市2002年TSP(总悬浮颗粒物)和SO2(二氧化硫)大气环境监测资料、污染源排放清单资料和气象资料以及新一代大气扩散模型，进行了本溪市大气环境质量区域评价。结果表明：本溪市低架源对地面浓度的贡献相对较大，高架源对地面浓度的贡献相对较小。 相似文献
8.
9.
10.
本文建立并论述了一种区域多源实用烟团轨迹模式。模式在作者先前工作的基础上,加进了对两个重要方面问题的处理,即:(1)运用质量连续风场调整的客观分析方法,得出三维风场并供作轨迹计算和扩散计算联接输入;(2)考虑风存在垂直切变的处理方案,使得模型更接近实际。对52×56km~2模拟域,含50个高架点源,非定常气象条件下的空气污染物输送与扩散作了计算,模式输出逐时网格风场和地面SO_2浓度分布以及日平均SO_2地面浓度分布与实测结果合理地一致。模式效能表明能够适应区域空气污染管理的需要。 相似文献
11.
Peter Hurley 《Boundary-Layer Meteorology》2007,125(3):525-536
The treatment of turbulence closure in atmospheric models is examined in the context of the dry convective boundary layer
(CBL) and the eddy-diffusivity/mass-flux (EDMF) approach. The EDMF approach is implemented into a model called TAPM to use
a coupled two-equation prognostic turbulence closure and the mass-flux approach to represent turbulence in the CBL. This work
also extends the range of turbulence variables that can be derived from the mass-flux component of the model and uses these
along with their values from the prognostic scheme to provide total turbulence fields that can be used to compare to data
and/or to feed into other components of TAPM, including those needed to drive Eulerian and Lagrangian air pollution dispersion
modules. Model results are presented for the afternoon of a simulated summer day and are compared to both laboratory and field
observations in a mixed-layer scaled framework. The results show that the EDMF approach works well within TAPM and can provide
good predictions of mean and turbulence fields, including in the upper levels of the CBL. The EDMF approach has several attractive
features, including the potential to be one approach to unify the treatment of turbulence and dry and moist convection in
atmospheric models. 相似文献
12.
山区复杂地形上区域大气质量模式的试验研究 总被引：3，自引：3，他引：3
由于复杂地形上的气流多变，所以，进行区域空气质量模拟是比较困难的。根据大气污染总量控制和环境规划的需要，发展了一种可适用于山谷城市的大气质量模式，该模式的主要特点；（１）采用目前尚少的复杂地形上的三维边界层模式作为大气扩散模式所需城三维边界层要素场；（２）用复杂地形上的三维以模式和斯扩散氏架源（包括面源）和主架源所造在的地面ＳＯ２浓度，然后将两者的模拟浓度在相应网各上叠加。验证结果表明，该混合模式 相似文献
13.
风切变对边界层对流影响的大涡模拟研究 总被引：5，自引：0，他引：5
利用"西北干旱区陆-气相互作用野外观测实验"加密观测期间在敦煌站的观测资料以及大涡模式,模拟了对流边界层的发展,以及示踪物从混合层向残留层传输的时空变化。模拟的对流边界层的结构及演变特征与实测结果基本一致。进一步通过有风切变和无风切变的敏感性数值试验,研究了风切变对垂直速度、位温和示踪物浓度的水平分布以及示踪物传输高度的影响。研究结果表明,在有风切变的试验中(甚至风切变仅存在于近地层中),对流边界层的增长加强,而且示踪物被传输的高度也较高。与浮力驱动的对流边界层相比,由浮力和风切变共同驱动的边界层中上升气流较弱而下沉气流较强,但前者的上升气流与下沉气流的分布在垂直方向上更为倾斜。由于夹卷作用的增强,浮力和风切变共同驱动的对流边界层较浮力驱动的对流边界层暖。在夹卷层,浮力和风切变共同驱动的边界层对流的上升气流和下沉气流都比浮力驱动的边界层对流中的强,而且垂直速度的概率密度函数分布也较对称,其位温和示踪物浓度的概率密度函数分布也比浮力驱动的边界层中的平直。对湍流动能收支的分析也表明风切变对湍流动能有重要影响,尤其对夹卷层中的湍流动能切变产生项影响较大。示踪物浓度的概率密度函数垂直分布显示,浮力驱动的边界层中示踪物浓度随高度变化较小,而浮力和风切变共同驱动的边界层中示踪物浓度随高度递减,但是示踪物传输的高度比较高。 相似文献
14.
Dispersion of passive tracer in the atmospheric convective boundary layer with wind shears: a review of laboratory and numerical model studies 总被引：2，自引：0，他引：2
E. Fedorovich 《Meteorology and Atmospheric Physics》2004,87(1-3):3-21
Summary Paper reviews recent laboratory and numerical model studies of passive gaseous tracer dispersion in the atmospheric convective boundary layer (CBL) with surface and elevated wind shears. Atmospheric measurement data used for validation of these two model techniques are briefly discussed as well. A historical overview is given of laboratory studies of dispersion in the atmospheric CBL. Model studies of tracer dispersion in two CBL types, the (i) non-steady, horizontally homogeneous CBL and (ii) quasi-stationary, horizontally heterogeneous CBL, are reviewed. The discussion is focused on the dispersion of non-buoyant plume emitted from a point source located at different elevations within the CBL. Approaches towards CBL modeling employed in different laboratory facilities (water tanks and wind tunnels) are described. The reviewed numerical techniques include Large Eddy Simulation (LES) and Lagrangian modeling. Numerical data on dispersion in the sheared CBL is analyzed in conjunction with experimental results from wind-tunnel CBLs. 相似文献
15.
为研究黄河源区边界层湍流特征及其对物质和能量输送的影响,本文首次采用大涡模拟的方法,对比分析了黄河源区两种不同下垫面上（鄂陵湖和湖边草地）对流边界层（CBL）中精细的湍流结构特征。使用资料为2012年夏季黄河源区鄂陵湖流域野外观测实验的GPS探空资料、涡动相关观测资料。分析表明,模拟的黄河源区草地和湖上CBL的平均结构与实测结果吻合较好,但草地和湖上CBL的湍流结构特征差异较明显。模拟结果显示,草地CBL内湍能收支、湍流特征量的时空分布和湍涡结构特征均与陆地上热力驱动CBL的研究结果一致;湖上CBL顶部存在明显的对流卷特征,且夹卷层的湍流强度比草地的强,而草地近地面湍强则更大。通过改变水平分辨率的模拟试验,发现两个不同下垫面上模拟结果对模式分辨率的敏感性不同,湖面CBL的模拟要选择较高的水平分辨率（50～100 m）,以提高近湖面和夹卷层对湍流动能和湍流通量模拟的精度,也充分模拟出各种尺度的波对湍流通量的累积贡献。考虑到计算时间等影响,模拟草地边界层精细的湍流结构时建议选择网格距为100～200 m。 相似文献
16.
城市建筑动力学效应对对流边界层影响的敏感性试验 总被引：3，自引：1，他引：2
本文将大涡模拟应用于城市对流边界层(CBL)湍流结构和流场特征的研究,在大涡模式中,拖曳系数取与建筑物高度及建筑物高度标准差有关的表达式以考虑次网格建筑物对风速和湍流动能(TKE)的面积平均影响.模拟结果表明,由于城市建筑物对气流的拖曳作用,使建筑物冠层及整个CBL内风速大幅度减小,城市冠层内部风速减小尤为明显,在夹卷层内,风速有一明显的跃变.在边界层中部对流运动已经发展成为较强的热泡,城市建筑物的动力学效应使热泡的水平尺度增大,CBL内平均上升气流速度和下沉气流速度减小,同时使CBL中上升气流所占比例比平坦地面增大.城市建筑物使CBL低层热通量、动量通量、速度方差和位温方差明显增大,但对近地层高度以上的湍流量影响不大. 相似文献
17.
Parameterization of Sheared Entrainment in a Well-developed CBL.Part Ⅱ:A Simple Model for Predicting the Growth Rate of the CBL 总被引：1，自引：0，他引：1
Following the parameterization of sheared entrainment obtained in the companion paper, Liu et al. (2016), the present study aims to further investigate the characteristics of entrainment, and develop a simple model for predicting the growth rate of a well-developed and sheared CBL. The relative stratification, defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone, is found to be a function of entrainment flux ratio (A e). This leads to a simple expression of the entrainment rate, in which A e needs to be parameterized. According to the results in Liu et al. (2016), A e can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL. The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations. Results indicate that the entrainment process is influenced by the dynamic effect, the interaction between mean shear and environmental stratification, and one other term that includes the Coriolis effect. These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL. This model is validated by outputs of LESs, and the results show that it performs satisfactorily. Compared with bulk models, this model does not need to solve a set of equations for the CBL. It is more convenient to apply in numerical models. 相似文献
18.
Alexander C. Taylor Robert J. Beare David J. Thomson 《Boundary-Layer Meteorology》2014,153(3):389-407
We investigate dispersion in the evening-transition boundary layer using large-eddy simulation (LES). In the LES, a particle model traces pollutant paths using a combination of the resolved flow velocities and a random displacement model to represent subgrid-scale motions. The LES is forced with both a sudden switch-off of the surface heat flux and also a more gradual observed evolution. The LES shows ‘lofting’ of plumes from near-surface releases in the pre-transition convective boundary layer; it also shows the subsequent ‘trapping’ of releases in the post-transition near-surface stable boundary layer and residual layer above. Given the paucity of observations for pollution dispersion in evening transitions, the LES proves a useful reference. We then use the LES to test and improve a one-dimensional Lagrangian Stochastic Model (LSM) such as is often used in practical dispersion studies. The LSM used here includes both time-varying and skewed turbulence statistics. It is forced with the vertical velocity variance, skewness and dissipation from the LES for particle releases at various heights and times in the evening transition. The LSM plume spreads are significantly larger than those from the LES in the post-transition stable boundary-layer trapping regime. The forcing from the LES was thus insufficient to constrain the plume evolution, and inclusion of the significant stratification effects was required. In the so-called modified LSM, a correction to the vertical velocity variance was included to represent the effect of stable stratification and the consequent presence of wave-like motions. The modified LSM shows improved trapping of particles in the post-transition stable boundary layer. 相似文献
19.
We use the Wind Farm Parameterization(WFP) scheme coupled with the Weather Research and Forecasting model under multiple resolution regimes to simulate turbulent wake dynamics generated by a real onshore wind farm and their influence at the local meteorological scale. The model outputs are compared with earlier modeling and observation studies. It is found that higher vertical and horizontal resolutions have great impacts on the simulated wake flow dynamics. The corresponding wind speed deficit and turbulent kinetic energy results match well with previous studies. In addition, the effect of horizontal resolution on near-surface meteorology is significantly higher than that of vertical resolution. The wake flow field extends from the start of the wind farm to downstream within 10 km, where the wind speed deficit may exceed 4%. For a height of 150 m or at a distance of about 25 km downstream, the wind speed deficit is around 2%. This indicates that, at a distance of more than 25 km downstream, the impact of the wind turbines can be ignored. Analysis of near-surface meteorology indicates a night and early morning warming near the surface, and increase in near-surface water vapor mixing ratio with decreasing surface sensible and latent heat fluxes. During daytime, a slight cooling near the surface and decrease in the near-surface water vapor mixing ratio with increasing surface sensible and latent heat fluxes is noticed over the wind farm area. 相似文献