考虑雾的微物理特征条件下的水雾扩散数值模拟研究

由于雾滴谱的不易获得，传统的水雾扩散研究一般不考虑其滴谱特征，而将其雾滴粒径作为常数处理。为此，引入实测的雾滴谱资料，考虑水雾在流专程 的扩散，蒸发及相变潜热对流场的反馈机制，利用三维非线性PLB方程组，采用工程上实用的湍流[E-ε]闭合方案，建立了一个高分辨率的PBL模式来模拟不同层结下，水电站泄洪产生的水务的扩散及共对环境湿度的影响，模拟结果表明，引入雾滴谱后的水雾扩散范围和相对湿度改变范围与不考虑雾滴谱条件下的相比，与日俱增接近实测，符合甚好。     

A three-dimensional prediction system for water qualitypolluction in coastal waters

ＩｎｔｒｏｄｕｃｔｉｏｎＨａｋａｔａＢａｙｉｓａｓｅｍｉ ｅｎｃｌｏｓｅｄｂａｙ(ｆｒｏｍ 33°34′Ｎｔｏ 33°41′Ｎａｎｄｆｒｏｍ 1 30°1 3′Ｅｔｏ 1 30°2 6′Ｅ)ｌｏｃａｔｅｄａｔｔｈｅｎｏｒｔｈｓｉｄｅｏｆＫｙｕｓｈｕＩｓｌａｎｄ ,Ｊａｐａｎ .ＴｈｅｌｅｎｇｔｈａｎｄｗｉｄｔｈｏｆＨａｋａｔａＢａｙｉｓａｂｏｕｔ2 0ｋｍａｎｄ 1 0ｋｍｒｅｓｐｅｃｔｉｖｅｌｙ .Ｔｈｅｓｕｒｆａｃｅａｒｅａｉｓａｂｏｕｔ 1 33ｋｍ2 ａｎｄｔｈｅｍｅａｎｗａｔｅｒｄｅｐｔｈｉｓａｂｏｕｔ1 0 .5ｍ .Ｔｈｅｂａｙｍｏｕｔ…     

紊动水体复氧规律研究

根据紊动扩散理论及气液界面质量传递过程，在对流场精确描述和对表面传质系数充分研究的基础上，建立了三维紊动水体复氧模型。模型充分考虑了流场及紊动特性对复氧影响。     

沿岸熏烟扩散的中尺度模拟系统

建立了一个沿岸熏扩散的中尺度模拟系统，它由一个二维二阶矩闭合的ＰＢＬ模式和一个随机流动扩散模式组成。初步的模拟和一些数值试验结果表明，随机游动扩散模式与现行的基于高斯扩散公式的熏烟扩散模式比较，其物理模型更为合理；采用二阶矩湍流闭合方案的ＰＢＬ模式能模拟得到合理的热力内边界层（ＴＩＢＬ）结构特征，将二阶矩湍流闭合ＰＢＬ模式模拟所得气象场作为随机游动扩散模式的气象输入，可以较好地预测沿岸地区日间持续     

Turbulence closure models and their application in RAMS

Turbulence closures are fundamental for modelling the atmospheric diffusion in numerical codes and the resulting eddy diffusivities are key parameters in describing the transport and dispersion in the boundary layer. In this work, four turbulence closure schemes have been applied for reproducing a neutral flow over schematic complex terrain using the meteorological model RAMS. Two of the closures, a one-equation (E-l) and a two-equations (E-) model, have been implemented in RAMS in alternative to the ones originally available. In these cases, an analytical method based on the similarity theory for the atmospheric surface layer and boundary layer is adopted to calculate the empirical constants of the turbulence closures. Some examples of numerical studies performed to simulate the flow and turbulence over a 3-D hill in wind-tunnel experiment in neutral stratification are presented and discussed. An intercomparison of simulations related to different closures is considered by analysing the main features of the flow over the hill and by comparing calculated vertical profiles of turbulent kinetic energy with measured ones.     

Large-scale turbulent structure of uniform shallow free-surface flows

The hydrodynamics of super- and sub-critical shallow uniform free-surface flows are assessed using laboratory experiments aimed at identifying and quantifying flow structure at scales larger than the flow depth. In particular, we provide information on probability distributions of horizontal velocity components, their correlation functions, velocity spectra, and structure functions for the near-water-surface flow region. The data suggest that for the high Froude number flows the structure of the near-surface layer resembles that of two-dimensional turbulence with an inverse energy cascade. In contrast, although large-scale velocity fluctuations were also present in low Froude number flow its behaviour was different, with a direct energy cascade. Based on our results and some published data we suggest a physical explanation for the observed behaviours. The experiments support Jirka’s [Jirka GH (2001) J Hydraul Res 39(6):567–573] hypothesis that secondary instabilities of the base flow may generate large-scale two-dimensional eddies, even in the absence of transverse gradients in the time-averaged flow properties.     

Stability and Mixing of a Vertical Axisymmetric Buoyant Jet in Shallow Water

The stability, mixing and effect of downstream control on axisymmetric turbulent buoyant jets discharging vertically into shallow stagnant water is studied using 3D Reynolds-averaged Navier–Stokes equations (RANS) combined with a buoyancy-extended k –ε model. The steady axisymmetric turbulent flow, temperature (or tracer concentration) and turbulence fields are computed using the finite volume method on a high resolution grid. The numerical predictions demonstrate two generic flow patterns for different turbulent heated jet discharges and environmental parameters (i) a stable buoyant discharge with the mixed fluid leaving the vertical jet region in a surface warm water layer; and (ii) an unstable buoyant discharge with flow recirculation and re-entrainment of heated water. A stratified counterflow region always appears in the far-field for both stable and unstable buoyant discharges. Provided that the domain radius L exceeds about 6H, the near field interaction and hence discharge stability is governed chiefly by the jet momentum length scale to depth ratio l_M/H, regardless of downstream control. The near field jet stability criterion is determined to be l_M/H = 3.5. A radial internal hydraulic jump always exists beyond the surface impingement region, with a 3- to 6-fold increase in dilution across the jump compared with vertical buoyant jet mixing. The predicted stability category, velocity and temperature/concentration fields are well-supported by experiments of all previous investigators.     

Turbulence-Based Models for Gas Transfer Analysis with Channel Shape Factor Influence

Gas transfer through surface water of streams is an effective process for the environmental quality of the aquatic ecosystem. Several theoretical approaches have been proposed to estimate gas transfer rate. This paper is devoted to present a turbulence-based model and to compare it with other 3 turbulence-based modeling frameworks that provide an estimation of gas-transfer coefficient K_L at the air-water interface. These models were derived for the reaeration process. In this paper, they have been verified both for reaeration and volatilization using experimental data collected in a laboratory rectangular flume and in a circular sewer reach. These data refer to oxygen absorption and cyclohexane volatilization, respectively. Comparison of results for oxygen shows that the tested models exhibit an average absolute difference between their results and the experimental data ranging from 12.5% and 25.6%. Also, the scaling analysis of the experimental data support both small-eddy based models and the model proposed by the authors. Moreover, volatilization results show that the process is also affected by a channel shape factor, which was, finally, quantified.     

The Modelling of Turbulence from Traffic in Urban Dispersion Models — Part II: Evaluation Against Laboratory and Full-Scale Concentration Measurements in Street Canyons

The paper addresses the problem of the parameterisation of traffic induced turbulent motion in urban dispersion models. Results from a variety of full-scale and wind-tunnel studies are analysed and interpreted within a modelling framework based on scaling considerations. The combined effects of traffic and wind induced dispersive motions are quantified for different traffic situations (variable traffic densities, vehicle velocities and vehicle types) and incorporated into the developed parameterisations. A new dispersive velocity scale is formulated and recommendations regarding its application in urban dispersion models are given. The necessity of accounting for traffic induced air motions in predictions of street-canyon pollution levels is demonstrated. Further research is needed to verify the empirical constants in the proposed parameterisations and to generalize the developed approach for a broader range of urban building configurations, meteorological conditions, and traffic situations.