凹坑地形风流结构对污染物散布的模拟研究

利用建立的三维非静力高分辨率高阶湍流闭合模式与随机游动扩散模式研究了一个深凹露天矿区污染物散布的规律,同时在风洞中进行了示踪实验。结果表明,由于凹坑内复环流结构的存在,使得坑内污染物浓度较大,且浓度最大值出现在源的上风侧。数值试验与风洞试验结果吻合较好。     

Evaluation of a micro-scale wind model’s performance over realistic building clusters using wind tunnel experiments

The simulation performance over complex building clusters of a wind simulation model(Wind Information Field Fast Analysis model, WIFFA) in a micro-scale air pollutant dispersion model system(Urban Microscale Air Pollution dispersion Simulation model, UMAPS) is evaluated using various wind tunnel experimental data including the CEDVAL(Compilation of Experimental Data for Validation of Micro-Scale Dispersion Models) wind tunnel experiment data and the NJU-FZ experiment data(Nanjing University-Fang Zhuang neighborhood wind tunnel experiment data). The results show that the wind model can reproduce the vortexes triggered by urban buildings well, and the flow patterns in urban street canyons and building clusters can also be represented. Due to the complex shapes of buildings and their distributions, the simulation deviations/discrepancies from the measurements are usually caused by the simplification of the building shapes and the determination of the key zone sizes. The computational efficiencies of different cases are also discussed in this paper. The model has a high computational efficiency compared to traditional numerical models that solve the Navier–Stokes equations, and can produce very high-resolution(1–5 m) wind fields of a complex neighborhood scale urban building canopy(～ 1 km ×1km) in less than 3 min when run on a personal computer.     

Large-Eddy Simulation of Windbreak Flow

A large-eddy simulation has been performed of turbulent flow around multiple windbreaks set within a wheat canopy under neutral stability conditions. The simulation is validated against a wind tunnel data set taken under similar conditions. Velocity profiles and second-order statistics are presented and compared to those found in the wind tunnel. From the numerical simulation, we discuss spatial distributions of instantaneous velocity fields and pressure statistics, which are important and telling features of the flow that are difficult to measure experimentally. We present a discussion of the momentum balance at various locations with respect to the windbreak, and similarly, we introduce the budget of a passive scalar. These discussions show the importance of the terms in each budget equation as they vary upstream and downstream of the windbreak.     

Measurements of the upstream turbulent flow during wind tunnel simulations of agricultural field burning

Mean streamwise and vertical velocities as well as streamwise and vertical turbulence intensities were measured in a combustion wind tunnel used to collect pollutant emission data for agricultural field burning. Objectives were to compare the flow field upstream of a fire to that without a fire present and to compare the wind tunnel flow upstream of a fire to field conditions. Vertical centerline traverses with an anemometer were conducted for 32 separate wind tunnel operating configurations (wind speed, position in the tunnel, with or without fire, ceiling position, and floor condition) with one replication for each configuration (total of 64 traverses). Certain configurational changes in the wind tunnel had substantial effects on the flow field. Turbulence intensities and velocity profiles (as modeled by the log law-of-the-wall to determinez ₀ andu _* values) in the wind tunnel were comparable to those in the field as reported in the literature. Velocities and turbulence intensities were generally higher, however, with a fire present in the tunnel and all other conditions constant.     

深凹露天矿内复环流和高湍能区的三维细网格非静力模拟

建立了一个准定常的三维非静力能量闭合的PBL模式模拟了深凹露天矿内复环流和高湍能区。针对露天矿具有范围小、地形复杂的特点,放弃了静力近似的假定,且采用了在复杂地形下应用较好的能量闭合方案,采用细网格系统对一个水平只有2 km×2 km的实际矿区进行了模拟,并将结果与同样条件下的风洞试验结果进行了比较。结果表明,矿坑的开口宽度与深度比和来流的性质对坑内气流和湍流情况有了较大影响。     

Numerical study of flow and gas diffusion in the near-wake behind an isolated building

To assist validation of the experimental data of urban pollution dispersion, the effect of an isolated building on the flow and gaseous diffusion in the wake region have been investigated numerically in the neutrally stratified rough-walled turbulent boundary layer. Numerical studies were carried out using Computational Fluid Dynamics (CFD) models. The CFD models used for the simulation were based on the steady-state Reynolds-Average Navier-Stoke equations (RANS) with κ-ε turbulence models; standard κ-ε and RNG κ-ε models. Inlet conditions and boundary conditions were specified numerically to the best information available for each fluid modeling simulation. A gas pollutant was emitted from a point source within the recirculation cavity behind the building model. The accuracy of these simulations was examined by comparing the predicted results with wind tunnel experimental data. It was confirmed that simulation using the model accurately reproduces the velocity and concentration diffusion fields with a fine-mish resolution in the near wake region. Results indicated that there is a good agreement between the numerical simulation and the wind tunnel experiment for both wind flow and concentration diffusion. The results of this work can help to improve the understanding of mechanisms of and simulation of pollutant transport in an urban environment.     

Flow in a Street Canyon for any External Wind Direction

An analytical model has been developed for the flow along a street canyon (of height H and width W), generated by an external wind blowing at any angle relative to the axis of the street. Initially, we consider the special case of a wind blowing parallel to the street. The interior of the street is decomposed into three regions, and the flow within each region is assumed to depend only on the external wind and the distance to the closest solid boundary. This decomposition leads to two different flow regimes: one for narrow streets (H/W > 1/2) and one for wide streets (H/W < 1/2). The theoretical model agrees well with results obtained from numerical simulations using a Reynolds-Averaged Navier–Stokes model. We then generalize the model to the case of arbitrary wind direction. Numerical solutions show that the streamlines of the mean flow in the street have a spiral form, and for most angles of incidence, the mass flux along the street scales on the component of the external wind resolved parallel to the street. We use this result to generalize the model derived for wind blowing parallel to the street, and the results from this model agree well with the numerical simulations. The model that has been developed can be evaluated rapidly using only very modest computing power, so it is suitable for use as an operational tool.     

局地废气排放污染影响的实验模拟

本文给出了一项在南京大学NJU环境风洞中实施的实验模拟研究。试验模拟一座位于城市街区的排放塔的废气排放，通过流场测量，放烟显示和示踪气体扩散试验，分析气流分布与污染物浓度分布，得出对局地环境影响的一些结论。文中还以模拟扩散试验资料为实验基础，建立修正的扩散模式，探讨污染物浓度预测的可靠途径。研究结果表明，风洞流体模拟手段是有成效且实用的。     

The Askervein Hill Project: Wind-tunnel simulations at three length scales

Wind-tunnel simulations of neutrally-stable atmospheric boundary-layer flow over an isolated, low hill (Askervein) have been carried out at three different length scales in two wind-tunnel facilities. The objectives of these simulations were to assess the reliability with which changes in mean wind and turbulence structure induced by the prototype hill on boundary-layer flow can be reproduced in the wind tunnel, and to determine the relative impact of certain modelling approaches (surface roughness, model scale, measurement techniques, etc.) on the quality of the simulations. The wind-tunnel results are compared with each other and with full-scale data and are shown in general to model the prototype flow very well. The effects of relaxing the criterion of aerodynamic roughness of the model surface were limited to certain regions in the lee of the hill and were linked to separation phenomena.     

Estimation of liquid water content effects on the air temperature measurements in the clouds based on the wind tunnel experiments

Presented are the results of experiments carried out in the wind tunnel and aimed at the investigation of characteristics of high-frequency aircraft thermometer constructed for studying the atmosphere from the board of the aircraft-laboratory. It is demonstrated that the values of recovery coefficient of the thermometer obtained both in the wind tunnel and after numerical experiments practically coincided with the values that have been measured before, during the flight testing. The flow with the specified values of liquid droplet content that was created in the wind tunnel, enabled to determine both the degree of effects made by the cloud on the measured temperature and its fluctuations and the value of the coefficient for introducing the correction to the temperature and its fluctuations in the cloud. It is shown that the taking account of effects made by liquid water content on the measured temperature is absolutely necessary for the correct interpretation of aircraft-based results of studying the thermodynamic structure of clouds.     

山地露天矿自然通风风流与湍流结构的数值模拟

利用建立的三维非力能量闭合的大气边界层数值模式，研究了中性层结条件下某露天矿自然通风的风流和湍流结构特征及影响因子。研究表明：坑内水平风场在坑底或采壁处受地形的影响很大，在矿采深与开口宽度比较小或者来流风速随高度的切变不大时，坑内气流为平直型，有利于通风；反之坑内则形成环流，且在环流范围内较大的湍能，不利于通风，易产生高浓度的污染物。本模式模拟的结果还与风洞模拟和高阶闭合模式模拟的结果作了检验比较     

Wake characterization downstream of a fog collector

The problem of wake geometry characterization downstream of a collector for getting water out of advection fog is investigated combining the results coming from wind tunnel trials and an experimental campaign in Peru (Lomas de Mejia), where a fog collection project was running. Results from a physical model of the fog collector at a 1:100 scale tested in a wind tunnel through anemometer velocity measurements and flow visualization techniques showed, at different heights from the ground, the general direction of the flow in the vicinity of the obstacle and the extension of the downstream-disturbed area. Wind speed data collection in Peru showed the reduction in wind speed depending on its intensity. The preliminary results show the utility of such an approach in order to improve the understanding of the flow motion downstream of permeable surfaces. The possibility of spatially characterizing the wake presence has a practical utilization whenever the knowledge of the geometry of the wake downstream of an obstacle is required.     

Boundary-layer flow over analytical two-dimensional hills: A systematic comparison of different models with wind tunnel data

Two mass consistent models (MATHEW and MINERVE) and two dynamic linearized models (MS3DJH/3R and FLOWSTAR) are used to simulate the mean flow over two-dimensional hills of analytical shape and of varying slope. The results are compared with detailed wind tunnel data (RUSHIL experiment at US EPA). Different numerical experiments have been performed, varying input data and control parameters, to test the data-processing methodology and to evaluate the minimum input data (for mass consistent models only) necessary to obtain a reliable flow field. The models behave differently according to the physical assumptions made and numerical procedure used: an assessment is then made in order to identify the proper solution for the different conditions of topography and wind data.     

Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL.     

风电场风机叶片覆冰气象条件及覆冰模型研究进展

随着我国风电行业的快速发展，覆冰已经成为严重威胁风电场安全稳定运行的因素之一，针对这一问题，国内外学者陆续开展了相关研究。综合现有研究成果，从覆冰概况、研究方法分类、影响覆冰的因素、风机叶片覆冰期特点等方面做了总结。大量的研究成果显示：影响风机叶片覆冰的气象因素主要为环境温度、相对湿度、风速、液态水含量（Liquid Water Content,LWC）和体积中径（Median Volume Diameter,MVD）等。此外，冰风洞试验和数值仿真模拟方面已有很多成果，而覆冰模型法的研究还较少，后续研究的重点是开展对高分辨率数值预报产品的订正研究，构建适用于本地的风机叶片覆冰模型，为风电场提前预警覆冰期以采取融冰措施、合理安排生产等提供科学参考。     

Operating ranges of mesoscale numerical models and meteorological wind tunnels for the simulation of sea and land breezes

The operating ranges of mesoscale numerical models and meteorological wind tunnels for sea- and land-breeze simulations are defined in this paper based on a review of the theoretical and practical limitations of these two approaches. Numerical-model operating ranges are limited by the choice of governing equations, the numerical methods used to solve the governing equations, the scales of the surface or atmospheric forcing and the atmospheric response, the specified grid resolution and domain size, and the available computer resources. Wind-tunnel operating ranges are limited by the dimensions of the simulated circulations and of the tunnel itself, the tunnel flow speed and turbulence characteristics, the temperature gradients within the tunnel, the lack of Coriolis force and moist processes, and the characteristics of the measurement instrumentation. The operating ranges of these two simulation methods are shown to overlap. In this common range, results of simulations from both approaches can be compared so as to strengthen the validity of the results and to help in the development and improvement of parameterizations of physical processes in numerical models. In addition, the coupling of meteorological wind tunnels and mesoscale numerical models offers a larger range of operating conditions than can be achieved by either approach alone. Together, they can be used in a hybrid form to predict atmospheric conditions at the scale of a few meters for complex terrain (e.g., buildings, hills, etc.) within larger mesoscale atmospheric flow regimes. In the case of sea and land breezes, the sea-land transition zone and coastal internal boundary layer can be studied using both approaches.     

Flow and Transport in the Obstacle Layer: First Results of the Micro-Scale Model MITRAS

A new atmospheric micro-scale chemistry, transport and stream model, MITRAS, has been developed within the Tropospheric Research Program (TFS). MITRAS is an obstacle resolving model solving simultaneously the governing equations for chemistry, pollutant transport including soot as well as for the flow and temperature field. The chemical reaction module is based on a simplified RACM mechanism. MITRAS has been tested against quality ensured wind tunnel data. The model results on soot and ozone concentrations as well as on the spatial representativeness of measurement sites underline the necessity for high-resolution flow simulations for case studies on close-to-source chemistry and pollutant transport within the urban canopy layer.     

Fluid mechanical aspects of the pollutant transport to coniferous trees

Forest decline in some parts of Europe gave rise to various environmental studies concerning the intake and uptake of pollutants in the ecosphere. As far as fluid mechanics is concerned, the current interest is centered on flow-induced phenomena, e.g., the flow-enhanced deposition of pollutants to trees. In order to understand better the mechanisms of pollutant dispersion and deposition to trees, wind tunnel experiments carried out with small real coniferous trees and model trees are summarized in this paper. The flow around single trees and tree stands, both in flat terrain and on hillsides, has been analysed. The measurements were performed with a two-component laser Doppler anemometer system installed in an atmospheric boundary-layer wind tunnel. A chemical tracer method based on an ammonia-manganese chloride reaction was applied to visualize the deposition patterns around trees and modeled forest stands.     

A Model Study of Three-Dimensional Wind Field Analysis from Dual-Doppler Radar Data

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