修正WRF次网格地形方案及其对风速模拟的影响

复杂地形区域风场模拟的准确率一直是风能研究领域的难点和重点。WRF模式是目前风能评估领域应用最广泛的天气数值模式之一,但该模式在复杂地形区域存在对平原、山谷风速高估且对山顶风速低估的系统性误差,并有研究建立次网格地形方案以订正误差。而次网格地形方案在不同水平分辨率下常出现错误的修正结果,该文基于高精度地形高程数据分析了方案失效的主要原因,发现其方程组中判断山体形态特征的阈值-20在过低和过高水平分辨率下均失去参考性。针对这一原因,将方案中影响关键参数C_t的地形高度算子与模式水平分辨率进行拟合,形成地形高度算子与水平分辨率相依赖的线性关系,获得不同分辨率下更适合的山体形态阈值。通过与自动气象站10 m风速对比分析了修正前后WRF对低层风速的模拟效果,结果显示:修正后的次网格地形方案能够分别在较低和较高分辨率下,部分矫正原方案错误的订正结果,使低层风速模拟更接近实况。修正后的次网格地形方案可为复杂地形区域开展高分辨率风场模拟提供参考。     

An Actively Controlled Wind Tunnel And Its Application To The Reproduction Of The Atmospheric Boundary Layer

An actively controlled wind tunnel equipped with multiple fansand airfoils has been developed, mainly for the purpose of reproducing the atmospheric boundary layer (ABL) for wind engineering applications. Various fluctuating flows can be achieved in this wind tunnel by altering the input data of the fans and airfoils through computer control. In this study, the ABL is physically simulated in this wind tunnel, and particular attention ispaid to the simulation of the profile of Reynolds stress. The method of generating the fluctuating flow and the experimental results of reproducing the ABL are presented. As the results show, the spatial distribution of Reynolds stress is satisfactorily simulated, and the profiles of other statisticalturbulent parameters, such as mean velocity, turbulent intensity, integral scale and power spectrum are successfully reproduced simultaneously.     

Double-camera measurements of plumes, applied to wind field characterization and dispersion studies

A stereophotogrammetric technique based on standard equipment to measure plume trajectories in sheared wind fields and/or complex terrain is shown here. The approach is to use existing visible plumes as tracers of opportunity of air flow. This technique was first developed as part of a multi-instrument field program intended for the experimental characterization of atmospheric dispersion in the complex coastal area of Bilbao in northern Spain. Emphasis is placed on the calibration method and the experimental procedures as well as on sources and margins of error. Finally, applications and joint usage with other techniques during several field programs are also presented.     

Remarks on the Definition and Estimation of Friction Velocity

One of the mainscaling parameters in similarity theory of the atmospheric boundary layer is friction velocity. Unfortunately, several definitions of friction velocity exist in the literature. Some authors use the component of the horizontal Reynolds stress vector in the direction of the mean wind vector to define friction velocity. Others define the friction velocity by means of the absolute value of the horizontal Reynolds stress vector. The two definitions coincide only if the direction of the mean wind vector is parallel to the horizontal Reynolds stress vector. In general, the second definition gives larger values for the friction velocity. Over complex terrain the situation is further complicated by the fact that the terrain following flow is not necessarily horizontal. Thus, several authors have proposed to use terrain following coordinate systems for the definition of friction velocity. By means of a large dataset of fast-response wind measurements with an ultrasonic anemometer the friction velocities resulting from the different definitions are compared. Furthermore, it is shown that friction velocity can be well estimated from horizontal wind speed, and even better from simple horizontal or vertical turbulence parameters.     

基于CFD技术的陡峭山体风场模拟方法研究

为更好将计算流体力学(CFD)技术应用于陡峭山体的风场模拟研究,文中对其中两个关键技术问题进行了研究,一是适宜的CFD解域顶高问题,二是入流边界条件设置方法问题。研究采用了香港国际机场的多普勒雷达径向速度观测资料,通过CFD模拟结果与观测结果对比验证展开研究。对于解域顶高,一般环境流体力学或建筑风工程领域要求顶高越高越好,例如5倍于地面障碍物的垂直高度,究其原因,主要是为了获得地面障碍物周边的整个流场结构,避免顶边界过低影响障碍物顶部流场的准确性。通过数值试验发现,若模拟关心的区域为较低海拔高度时,不必完全拘泥于该要求,对一座高度为1000m量级的山体进行模拟,顶高为3000和6000m的两组试验在边界层中低部给出的模拟结果没有显著差别。进行了3组边界条件设置方法的对比试验,结果表明单纯采用廓线法不足以充分描述来流信息,二维插值法尽管提供了更高分辨率的边界数据,但其结果总体上逊于0维插值法。研究表明,CFD可以很好地描述山地激发的涡旋/波动脱体运动,比单纯采用中尺度模式效果要好得多。在利用CFD工具研究复杂山地风场时,应本着"实用主义"的精神设置物理模型、参数和选取适当的方法、边界条件,以达到模拟精度和计算量的优化平衡,并足以用于研究所关心的具体问题。     

Sensitivity of Turbine-Height Wind Speeds to Parameters in Planetary Boundary-Layer and Surface-Layer Schemes in the Weather Research and Forecasting Model

We evaluate the sensitivity of simulated turbine-height wind speeds to 26 parameters within the Mellor–Yamada–Nakanishi–Niino (MYNN) planetary boundary-layer scheme and MM5 surface-layer scheme of the Weather Research and Forecasting model over an area of complex terrain. An efficient sampling algorithm and generalized linear model are used to explore the multiple-dimensional parameter space and quantify the parametric sensitivity of simulated turbine-height wind speeds. The results indicate that most of the variability in the ensemble simulations is due to parameters related to the dissipation of turbulent kinetic energy (TKE), Prandtl number, turbulent length scales, surface roughness, and the von Kármán constant. The parameter associated with the TKE dissipation rate is found to be most important, and a larger dissipation rate produces larger hub-height wind speeds. A larger Prandtl number results in smaller nighttime wind speeds. Increasing surface roughness reduces the frequencies of both extremely weak and strong airflows, implying a reduction in the variability of wind speed. All of the above parameters significantly affect the vertical profiles of wind speed and the magnitude of wind shear. The relative contributions of individual parameters are found to be dependent on both the terrain slope and atmospheric stability.     

多元回归法在复杂地形风资源微尺度模拟中的应用

随着风电事业的发展,复杂地形下的风资源模拟成为一项重要的课题。利用广东沿海某海岛南部9个测风塔共22个测风高度的完整一年的测风资料及该海岛高分辨率的数字地形资料,采用地理空间因子的多元回归法进行风资源的微尺度模拟并与WASP软件的计算结果进行了比较。结果表明：（1）年平均风速与地理空间因子存在显著的相关关系;（2）模拟的年平均风速平均相对误差为3.2%,年平均风功率密度的平均相对误差为3.5%;（3）经假设检验,对无测站的地点的年平均风速模拟效果良好;（4）该方法和WASP软件计算的风资源大值区分布基本一致。     

A new large-eddy simulation model for simulating air flow and warm clouds above highly complex terrain. Part I: The dry model

This paper presents the dry version of a new large-eddy simulation (LES) model, which is designed to simulate air flow and clouds above highly complex terrain. The model is three-dimensional and nonhydrostatic, and the governing equations are sound filtered by use of the anelastic approximation. A fractional step method is applied to solve the equations on a staggered Cartesian grid. Arbitrarily steep and complex orography can be accounted for through the method of viscous topography. The dynamical model core is validated by comparing the results for a spreading density current against a benchmark solution. The model accuracy is further assessed through the simulation of turbulent flow across a quasi two-dimensional ridge. The results are compared with wind-tunnel data. The method of viscous topography is not restricted to moderately sloped terrain. Compared to models using curvilinear grids, it allows this model to be applied to a much wider range of flows. This is illustrated through the simulation of an atmospheric boundary-layer flow over a surface mounted cube. The results show that the dry model version is able to accurately represent the complex flow in the vicinity of three-dimensional obstacles. It is concluded that the method of viscous topography was successfully implemented into a micrometeorological LES model. As will be shown in Part II, this allows the detailed study of clouds in highly complex terrain.     

基于大涡模拟的冬奥赛区风环境精细化评估

风是北京冬奥会场外赛事考虑的首要气象因素, 精细评估竞赛场地核心区域风环境对赛道施工建设、遴选防风方案及赛事安排非常必要。以北京冬奥会延庆赛区为中心, 将2009—2021年冬奥赛事月份(2—3月)天气环流场进行客观天气环流分型(分为93组), 采用北京城市气象研究院睿图-大涡模式系统对各组的典型个例开展37 m×37 m分辨率风场模拟。利用赛道周边12个自动气象站数据检验结果显示: 2 m温度、10 m风速和风向平均偏差分别为0.45℃, 1.51 m·s-1, 11.23°, 预报技巧较高。基于分型模拟数据获得赛场平均风、极大风分布及大风风险概率, 高山滑雪赛场赛道起点平均风速为15 m·s-1, 超出影响决策点概率为60%, 风险较大; 而赛道中、后段风险较小, 超过影响决策风速概率小于2%。     

西宁市大气环境风险模拟研究

利用中尺度气象模式模拟了特殊地形下的气象变化特征,通过CALPUFF模拟了大气环境风险事件的精细化扩散特征。结果表明：西宁市地面风特征与河谷地形走向基本一致,典型风场表现为湟水河谷盛行西北和东南风,北川河谷则多为偏北风。由于青藏高原昼间强烈的山坡辐射增热和致使低空出现逆温层频率高,强度大,不利于污染物在垂直方向的扩散,河谷剖面模拟温度场的结果显示等高度山坡附近比河谷中心的温度大约高1.5℃。CALPUFF烟团轨迹模式能较好地应用于西宁市大气环境风险事件的模拟研究,模拟结果能清楚描绘出污染物沿河谷输送与扩散的初始状况和细致分布,同时在复杂地形和气象条件影响下出现山体对烟团的阻碍效应、烟团因流场在山脊处出现形变以及山谷风环流影响等非定常扩散现象,扩散轨迹符合复杂地形和气象条件影响的特征和规律,模拟结果对准确预估大气环境风险事件在复杂地形和气象条件下城市中的扩散特征、影响范围和程度具有重要意义。     

Large-Eddy Simulations of Atmospheric Flows Over Complex Terrain Using the Immersed-Boundary Method in the Weather Research and Forecasting Model

Atmospheric flow over complex terrain, particularly recirculation flows, greatly influences wind-turbine siting, forest-fire behaviour, and trace-gas and pollutant dispersion. However, there is a large uncertainty in the simulation of flow over complex topography, which is attributable to the type of turbulence model, the subgrid-scale (SGS) turbulence parametrization, terrain-following coordinates, and numerical errors in finite-difference methods. Here, we upgrade the large-eddy simulation module within the Weather Research and Forecasting model by incorporating the immersed-boundary method into the module to improve simulations of the flow and recirculation over complex terrain. Simulations over the Bolund Hill indicate improved mean absolute speed-up errors with respect to previous studies, as well an improved simulation of the recirculation zone behind the escarpment of the hill. With regard to the SGS parametrization, the Lagrangian-averaged scale-dependent Smagorinsky model performs better than the classic Smagorinsky model in reproducing both velocity and turbulent kinetic energy. A finer grid resolution also improves the strength of the recirculation in flow simulations, with a higher horizontal grid resolution improving simulations just behind the escarpment, and a higher vertical grid resolution improving results on the lee side of the hill. Our modelling approach has broad applications for the simulation of atmospheric flows over complex topography.     

城市中水体布局对大气环境的影响

城市下垫面状况在很大程度上决定城市大气物理环境的特征。在城市区域增加湿地等自然地表有利于城市的减温增湿,促使局地流场发生变化,改善局地微气象条件以及大气物理环境。城市规划大气物理环境多尺度数值模拟系统为城市规划大气物理环境定量评估提供了有效的模拟工具。利用该系统中的城市尺度模式模拟了水体布局为集中型和分散型,水体面积占有率分别为4%、8%、12%和16%条件下,城市大气温度、湿度、风速、城市大气扩散条件的变化及其对城市大气环境的影响,利用北京市城市水体气象观测数据,分析了水体周边和商业区、交通区温、湿度的差异,并对模式模拟结果进行了验证,揭示了城市水体布局对城市大气物理环境影响的可能机制。模拟和观测结果显示,城市水体布局会对城市微气象环境产生一定影响。无论分散型或集中型布局,城市水体面积的增加,都在一定程度上使城市气温降低、湿度增加、平均风速增大。比较而言,分散型水体布局对城市区域微气象环境的影响更为显著。     

风廓线雷达探测大气返回信号谱的仿真模拟

利用2008年1—9月北京延庆地区对流层CFL-08风廓线雷达和2009年7—12月广东东莞地区边界层CFL-03风廓线雷达晴空大气探测资料,对大气返回信号功率谱密度分布及雷达系统噪声幅度统计特征进行分析。基于大气返回信号的谱分布符合高斯分布的统计结果,采用高斯模型对大气返回信号谱进行模拟;雷达系统噪声是白噪声,其谱线幅度的统计特征呈高斯分布,在此基础上,通过生成高斯分布随机函数对雷达探测输出信号进行信号谱分布的仿真模拟,并采用雷达探测信号的谱参数对仿真模拟进行检验,效果较好。该文应用仿真模拟的数据,对风廓线雷达信息处理方法及其处理精度进行了初步试验和分析。     

Flow over Hills: A Large-Eddy Simulation of the Bolund Case

Simulation of local atmospheric flows around complex topography is important for several applications in wind energy (short-term wind forecasting and turbine siting and control), local weather prediction in mountainous regions and avalanche risk assessment. However, atmospheric simulation around steep mountain topography remains challenging, and a number of different approaches are used to represent such topography in numerical models. The immersed boundary method (IBM) is particularly well-suited for efficient and numerically stable simulation of flow around steep terrain. It uses a homogenous grid and permits a fast meshing of the topography. Here, we use the IBM in conjunction with a large-eddy simulation (LES) and test it against two unique datasets. In the first comparison, the LES is used to reproduce experimental results from a wind-tunnel study of a smooth three-dimensional hill. In the second comparison, we simulate the wind field around the Bolund Hill, Denmark, and make direct comparisons with field measurements. Both cases show good agreement between the simulation results and the experimental data, with the largest disagreement observed near the surface. The source of error is investigated by performing additional simulations with a variety of spatial resolutions and surface roughness properties.     

对流边界层中过山气流的数值模拟

采用ARPS4.0非静力中尺度气象模式模拟了对流边界层中气流过山引起的地形波,讨论了地形及大气条件改变对其的影响.模拟表明,当大气边界层是对流边界层时,气流过山引起的地形强迫,仍能在上部稳定层结中造成足够的垂直扰动,产生向上传播的重力内波,重力内波引起的波动阻力仍不可忽略.     

Non-Gaussian Lagrangian Stochastic Model for Wind Field Simulation in the Surface Layer

Wind field simulation in the surface layer is often used to manage natural resources in terms of air quality, gene flow(through pollen drift), and plant disease transmission(spore dispersion). Although Lagrangian stochastic(LS) models describe stochastic wind behaviors, such models assume that wind velocities follow Gaussian distributions. However,measured surface-layer wind velocities show a strong skewness and kurtosis. This paper presents an improved model, a non-Gaussian LS model, which inco...     

Wind Climate Simulation over Complex Terrain and Wind Turbine Energy Output Estimation

Summary A statistical-dynamical downscaling procedure is applied to investigate the climatological wind field over a complex terrain area in central Germany. The model domain, 80×87 km, is dominated by flat terrain in the westerly and northerly part and encompasses the Teuteburger Wald and the Wiehengebirge areas with hills up to 330 m a.m.s.l. in the southeasterly region. The downscaling procedure combines a large-scale regionally representative wind statistic and a high-resolution numerical atmospheric mesoscale model. A cluster analysis of a 12-years time series of radiosonde data provides 143 clusters each being a combination of the geostrophic wind components and the vertical temperature gradient. These parameter sets constitute the reference state for highly-resolved steady-state wind field simulations with a non-hydrostatic model. Weighting the resulting wind fields with the corresponding cluster frequency gives climatologically representative frequency distributions of the wind speed and -direction. By combining the wind speed frequency distribution with the power curve of wind turbines the yearly energy output of 46 wind turbines inside the simulation domain was calculated and compared to the actual production. No bias or systematic trend in the deviation was found. The relative differences for the smallest turbines reach 100 percent with a decreasing tendency to larger units. Received November 13, 1998     

WindSim软件在复杂地形风电场风能资源评估中的应用

复杂地形的风能资源评估研究对于风电事业的发展具有极为重要的意义。作者利用基于计算流体力学(CFD)方法的风能资源评估系统软件WindSim对我国复杂地形新疆托克逊县境内某风电场2007年的风资源情况进行了模拟,并将模拟结果与测风塔观测结果进行对比分析。模拟结果表明,WindSim软件对我国复杂地形地区平均风速的模拟能力比较好,10m、40 m、50 m、70 m高度的月平均风速的平均相对误差分别是12.91%、10.21%、9.68%、12.91%。同时,WindSim软件不仅可以较为准确地模拟出该区域2007年的主导风向,而且对该年的有效风速频率的模拟效果也很好。此风电场风能资源模拟试验说明,该地区具有十分丰富的可供开发利用的风能资源,进一步说明WindSim软件对我国复杂地形地区的风能资源评估工作具有很好的参考和应用价值。     

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     

汾河谷地大气环境容量与大气污染过程的数值模拟与敏感性分析

对汾河谷地及太原市在2015年1月的一次重污染过程运用WRF-Chem模式进行污染过程的数值模拟、观测验证和地形敏感性实验,分析了河谷地形对区域污染过程和大气环境容量的影响机制。结果表明:太原市及周边汾河谷地大气边界层环流和大气污染传输受天气系统、地形和城市化共同影响;地形环流强度明显强于太原城市热岛环流,且对其发展存在明显抑制作用,从而限制了城市大气环境容量,加剧城市近地面大气污染物的堆积和空气质量恶化;研究区域大气环境容量受气象主导风向影响:当天气主导风向偏南北向,也即与狭长的汾河谷地走向一致时,有利于该区域大气污染物的扩散清除,而当天气主导风向偏东西向时,则该区域大气环境容量明显减小,且近地面大气污染物浓度与大气环境容量之间呈强相关性,相关系数达到0.74;当地形敏感组实验中取消太原市周边河谷地形特征时,上述相关系数降低到0.21。