共查询到20条相似文献,搜索用时 46 毫秒
1.
The convective boundary layer (CBL) with a wide range of stability is simulated experimentally using a thermally stratified wind tunnel, and numerically by direct numerical simulation (DNS). The turbulence structures and flow characteristics of various CBL flows, capped by a strong temperature inversion and affected by surface shear, are investigated. The various vertical profiles of turbulence statistics similar to those from the observed CBL in the field are successfully simulated in both the wind-tunnel experiment and in DNS. The comparison of the wind-tunnel data and DNS results with those of atmospheric observations and water-tank studies shows the crucial dependence of the turbulence statistics in the upper part of the layer on the strength of the inversion layer, as well as the modification of the CBL turbulence regime by the surface shear. 相似文献
2.
The wake characteristics of a wind turbine for different regimes occurring throughout the diurnal cycle are investigated systematically by means of large-eddy simulation. Idealized diurnal cycle simulations of the atmospheric boundary layer are performed with the geophysical flow solver EULAG over both homogeneous and heterogeneous terrain. Under homogeneous conditions, the diurnal cycle significantly affects the low-level wind shear and atmospheric turbulence. A strong vertical wind shear and veering with height occur in the nocturnal stable boundary layer and in the morning boundary layer, whereas atmospheric turbulence is much larger in the convective boundary layer and in the evening boundary layer. The increased shear under heterogeneous conditions changes these wind characteristics, counteracting the formation of the night-time Ekman spiral. The convective, stable, evening, and morning regimes of the atmospheric boundary layer over a homogeneous surface as well as the convective and stable regimes over a heterogeneous surface are used to study the flow in a wind-turbine wake. Synchronized turbulent inflow data from the idealized atmospheric boundary-layer simulations with periodic horizontal boundary conditions are applied to the wind-turbine simulations with open streamwise boundary conditions. The resulting wake is strongly influenced by the stability of the atmosphere. In both cases, the flow in the wake recovers more rapidly under convective conditions during the day than under stable conditions at night. The simulated wakes produced for the night-time situation completely differ between heterogeneous and homogeneous surface conditions. The wake characteristics of the transitional periods are influenced by the flow regime prior to the transition. Furthermore, there are different wake deflections over the height of the rotor, which reflect the incoming wind direction. 相似文献
3.
Results of numerical simulations using the WRF-ARW nonhydrostatic model are presented for eight episodes of intense convection over European Russia in the summer of 2007. The calculations were performed on four nested grids with horizontal grid meshes of 27, 9, 3, and 1 km. Convection was parametrized on the first two grids and explicitly resolved on the other two. It has been found that simulations on finer grids with explicit calculation of convective flows make it possible to reproduce heavy rainfalls and strong-wind zones in the areas of intense convection. A preliminary verification of the short-range predictions of convective systems shows that the maximum 12-h precipitation totals and the maximum winds at 10 m are close, in the order of magnitude, to the observed values. Prediction of convection centers is the weakest point. Difficulties in the model verification associated with the absence of data with high space-time resolution are discussed. 相似文献
4.
Ning Zhang Quinton L. Williams Heping Liu 《Theoretical and Applied Climatology》2010,102(3-4):307-317
Landscape heterogeneity that causes surface flux variability plays a very important role in triggering mesoscale atmospheric circulations and convective weather processes. In most mesoscale numerical models, however, subgrid-scale heterogeneity is somewhat smoothed or not adequately accounted for, leading to artificial changes in heterogeneity patterns (e.g., patterns of land cover, land use, terrain, and soil types and soil moisture). At the domain-wide scale, the combination of losses in subgrid-scale heterogeneity from many adjacent grids may artificially produce larger-scale, more homogeneous landscapes. Therefore, increased grid spacing in models may result in increased losses in landscape heterogeneity. Using the Weather Research and Forecasting model in this paper, we design a number of experiments to examine the effects of such artificial changes in heterogeneity patterns on numerical simulations of surface flux exchanges, near-surface meteorological fields, atmospheric planetary boundary layer (PBL) processes, mesoscale circulations, and mesoscale fluxes. Our results indicate that the increased heterogeneity losses in the model lead to substantial, nonlinear changes in temporal evaluations and spatial patterns of PBL dynamic and thermodynamic processes. The decreased heterogeneity favor developments of more organized mesoscale circulations, leading to enhanced mesoscale fluxes and, in turn, the vertical transport of heat and moisture. This effect is more pronounced in the areas with greater surface heterogeneity. Since more homogeneous land-surface characteristics are created in regional models with greater surface grid scales, these artificial mesoscale fluxes may have significant impacts on simulations of larger-scale atmospheric processes. 相似文献
5.
The wake characteristics of a wind turbine in a turbulent atmospheric boundary layer under different thermal stratifications are investigated by means of large-eddy simulation with the geophysical flow solver EULAG. The turbulent inflow is based on a method that imposes the spectral energy distribution of a neutral boundary-layer precursor simulation, the turbulence-preserving method. This method is extended herein to make it applicable for different thermal stratification regimes (convective, stable, neutral) by including suitable turbulence assumptions, which are deduced from velocity fields of a diurnal-cycle precursor simulation. The wind-turbine-wake characteristics derived from simulations that include the parametrization result in good agreement with diurnal-cycle-driven wind-turbine simulations. Furthermore, different levels of accuracy are tested in the parametrization assumptions, representing the thermal stratification. These range from three-dimensional matrices of the precursor-simulation wind field to individual values. The resulting wake characteristics are similar, even for the simplest parametrization set-up, making the diurnal-cycle precursor simulation non-essential for the wind-turbine simulations. Therefore, the proposed parametrization results in a computationally fast, simple, and efficient tool for analyzing the effects of different thermal stratifications on wind-turbine wakes by means of large-eddy simulation. 相似文献
6.
D. Pavlidis G. J. Gorman J. L. M. A. Gomes C. C. Pain H. ApSimon 《Boundary-Layer Meteorology》2010,136(2):285-299
The computational fluid dynamics code Fluidity, with anisotropic mesh adaptivity, is used as a multi-scale obstacle-accommodating
meteorological model. A novel method for generating realistic inlet boundary conditions based on the view of turbulence as
a superposition of synthetic eddies is adopted. It is able to reproduce prescribed first-order and second-order one-point
statistics and turbulence length scales. The aim is to simulate an urban boundary layer. The model is validated against two
standard benchmark tests: a plane channel flow numerical simulation and a flow past a cube physical simulation. The performed
large-eddy simulations are in good agreement with both reference models giving confidence that the model can be used to successfully
simulate urban atmospheric flows. 相似文献
7.
Flow over Hills: A Large-Eddy Simulation of the Bolund Case 总被引:6,自引:6,他引:0
Marc Diebold Chad Higgins Jiannong Fang Andreas Bechmann Marc B. Parlange 《Boundary-Layer Meteorology》2013,148(1):177-194
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. 相似文献
8.
非均匀网格的过渡湍流理论及其在大气边界层数值模拟中的应用 总被引:1,自引:1,他引:1
本文将Stull提出的均匀网格下的过渡湍流理论推广到非均匀网格情形,推广的非均匀网格的过渡湍流理论满足Stull提出的对过渡矩阵系数的要求并具有清晰的物理意义。然后,将非均匀网格的过渡湍流理论应用于一维大气边界层数值模式中,对Wangara资料进行了模拟,并与均匀网格情形进行了对比。计算表明,非均匀网格的过渡湍流模式能很好地模拟Wangara大气边界层平均量与湍流量的变化;本文非均匀网格的过渡湍流理论的推广是可行的,它可能会在大气边界层数值模拟及其他方面(如:中尺度模式)得到应用。 相似文献
9.
Characteristics and Numerical Simulations of Extremely Large Atmospheric Boundary-layer Heights over an Arid Region in North-west China 总被引:3,自引:0,他引:3
Over arid regions in north-west China, the atmospheric boundary layer can be extremely high during daytime in late spring
and summer. For instance, the depth of the observed convective boundary layer can exceed 3,000 m or even be up to 4,000 m
at some stations. In order to characterize the atmospheric boundary-layer (ABL) conditions and to understand the mechanisms
that produce such an extreme boundary-layer height, an advanced research version of the community weather research and forecasting
numerical model (WRF) is employed to simulate observed extreme boundary-layer heights in May 2000. The ability of the WRF
model in simulating the atmospheric boundary layer over arid areas is evaluated. Several key parameters that contribute to
the extremely deep boundary layer are identified through sensitivity experiments, and it is found that the WRF model is able
to capture characteristics of the observed deep atmospheric boundary layer. Results demonstrate the influence of soil moisture
and surface albedo on the simulation of the extremely deep boundary layer. In addition, the choice of land-surface model and
forecast lead times also plays a role in the accurate numerical simulation of the ABL height. 相似文献
10.
一个对流边界层大涡模式的建立与调试 总被引:12,自引:4,他引:12
本文介绍一个适合于对流边界层的大涡模式的建立及其调试结果。该大涡模式建立过程中注重于计算的节省,同时也强调原理与方法的简单和合理性。模式的调试表明,对于平坦均一地形的情况,模拟可以获得合理的结果。调试同时显示了模式对较低水平分辨率的适用条件,以及模式应用于模拟较大水平范围问题的可能性。 相似文献
11.
The turbulence field obtained using a large-eddy simulation model is used to simulate particle dispersion in the convective
boundary layer with both forward-in-time and backward-in-time modes. A Lagrangian stochastic model is used to treat subgrid-scale
turbulence. Results of forward dispersion match both laboratory experiments and previous numerical studies for different release
heights in the convective boundary layer. Results obtained from backward dispersion show obvious asymmetry when directly compared
to results from forward dispersion. However, a direct comparison of forward and backward dispersion has no apparent physical
meaning and might be misleading. Results of backward dispersion can be interpreted as three-dimensional or generalized concentration
footprints, which indicate that sources in the entire boundary layer, not only sources at the surface, may influence a concentration
measurement at a point. Footprints at four source heights in the convective boundary layer corresponding to four receptors
are derived using forward and backward dispersion methods. The agreement among footprints derived with forward and backward
methods illustrates the equivalence between both approaches. The paper shows explicitly that Lagrangian simulations can yield
identical footprints using forward and backward methods in horizontally homogeneous turbulence. 相似文献
12.
Domingo Muñoz-Esparza Branko Kosović Clara García-Sánchez Jeroen van Beeck 《Boundary-Layer Meteorology》2014,151(3):453-478
The applicability of the one-way nesting technique for numerical simulations of the heterogeneous atmospheric boundary layer using the large-eddy simulation (LES) framework of the Weather Research and Forecasting model is investigated. The focus of this study is on LES of offshore convective boundary layers. Simulations were carried out using two subgrid-scale models (linear and non-linear) with two different closures [diagnostic and prognostic subgrid-scale turbulent kinetic energy (TKE) equations]. We found that the non-linear backscatter and anisotropy model with a prognostic subgrid-scale TKE equation is capable of providing similar results when performing one-way nested LES to a stand-alone domain having the same grid resolution but using periodic lateral boundary conditions. A good agreement is obtained in terms of velocity shear and turbulent fluxes, while velocity variances are overestimated. A streamwise fetch of 14 km is needed following each domain transition in order for the solution to reach quasi-stationary results and for the velocity spectra to generate proper energy content at high wavelengths, however, a pile-up of energy is observed at the low-wavelength portion of the spectrum on the first nested domain. The inclusion of a second nest with higher resolution allows the solution to reach effective grid spacing well within the Kolmogorov inertial subrange of turbulence and develop an appropriate energy cascade that eliminates most of the pile-up of energy at low wavelengths. Consequently, the overestimation of velocity variances is substantially reduced and a considerably better agreement with respect to the stand-alone domain results is achieved. 相似文献
13.
尽管经典台风强度理论是基于梯度风平衡模型,但是已有的飞机观测资料和数值模拟研究发现,边界层中和眼墙附近存在非梯度风平衡气流,前人数值模拟发现,眼墙附近最大的超梯度风可以达到切向风速的16.7%。大涡模拟可以模拟出滚涡和龙卷尺度涡旋等小尺度系统,这些小尺度系统对梯度风平衡可能产生影响,使用中尺度天气预报模式结合大涡模拟(WRF-LES)对模拟台风内核区域方位角平均的梯度风平衡进行了分析,三个大涡模拟试验的水平分辨率分别为333 m、111 m和37 m,结果表明非梯度风平衡气流并未因为分辨率提高而显著增强或产生结构差异,最大超梯度风出现在边界层顶处最大切向风半径的内侧,达到梯度风速的10.8%~16.1%。进一步分析发现,不同台风中心定位方法会影响非梯度风平衡气流,最小气压方差法和最大切向风法可以得到与前人模拟一致的结构,而气压权重法得到的低层超梯度风中心远离眼墙、靠近台风中心,位涡权重法得到的低层超梯度风的径向范围向内扩大,最小气压方差法和最大切向风法更适合用于梯度风平衡研究中的台风中心定位。 相似文献
14.
Raj K. Rai Larry K. Berg Branko Kosović Jeffrey D. Mirocha Mikhail S. Pekour William J. Shaw 《Boundary-Layer Meteorology》2017,163(1):69-89
The Weather Research and Forecasting (WRF) model can be used to simulate atmospheric processes ranging from quasi-global to tens of m in scale. Here we employ large-eddy simulation (LES) using the WRF model, with the LES-domain nested within a mesoscale WRF model domain with grid spacing decreasing from 12.15 km (mesoscale) to 0.03 km (LES). We simulate real-world conditions in the convective planetary boundary layer over an area of complex terrain. The WRF-LES model results are evaluated against observations collected during the US Department of Energy-supported Columbia Basin Wind Energy Study. Comparison of the first- and second-order moments, turbulence spectrum, and probability density function of wind speed shows good agreement between the simulations and observations. One key result is to demonstrate that a systematic methodology needs to be applied to select the grid spacing and refinement ratio used between domains, to avoid having a grid resolution that falls in the grey zone and to minimize artefacts in the WRF-LES model solutions. Furthermore, the WRF-LES model variables show large variability in space and time caused by the complex topography in the LES domain. Analyses of WRF-LES model results show that the flow structures, such as roll vortices and convective cells, vary depending on both the location and time of day as well as the distance from the inflow boundaries. 相似文献
15.
长江下游地区不同边界层参数化方案的试验研究 总被引:8,自引:5,他引:8
利用中尺度数值模式WRFV3.1.1中的MYJ、QNSE、YSU、ACM2、MYNN2.5、MYNN3、Boulac七种不同边界层参数化方案,进行了发生在长江下游地区的3例暴雨的模拟试验.重点分析比较了七个不同边界层参数化方案对降水总量分布、次降水区的边界层结构、关键基本气象要素场的模拟能力,并将降水总量和关键基本气象要素场的模拟结果与实测结果进行了统计检验.通过对比,发现QNSE方案的模拟能力相对优于其他边界层参数化方案. 相似文献
16.
17.
We have investigated the role of convective parameterization in simulations of heavy precipitation systems at grey-zone (2–10 km) resolutions using an approach similar to that used in “observing system simulation experiment”. Simulations with a 1-km grid serve as benchmark simulations. The impacts of convective parameterization at greyzone resolutions (i.e., 3, 6, and 9 km) are then investigated. This study considers two heavy precipitation systems including one associated with a mesoscale cyclone generated over the Shandong Peninsula on 24–25 July 1991, and the other associated with a cloud cluster occurred on 15–16 July 2009. The present study indicates that convective parameterization does not affect much the simulations of the two heavy precipitation systems with 3-km grid size. However, it significantly affects simulations for grid sizes of 6 and 9 km. Simulations with the Kain-Fritsch scheme produce deficiencies such as relatively small heavy rainfall area, smaller maximum precipitation rate, wider area of weak precipitation, etc. Simulations without convective parameterization have also some negative effects such as the overprediction of area-averaged precipitation rate and others. A modified trigger function in the Kain-Fritsch scheme is found to improve the simulations of the heavy precipitation systems over the Korean Peninsula by reducing excessive trigger of convection, especially for simulations with 6- and 9- km grids. 相似文献
18.
Terrain characteristics can be accurately represented in spectrum space. Terrain spectra can quantitatively reflect the effect of topographic dynamic forcing on the atmosphere. In wavelength space, topographic spectral energy decreases with decreasing wavelength, in spite of several departures. This relationship is approximated by an exponential function. A power law relationship between the terrain height spectra and wavelength is fitted by the least-squares method, and the fitting slope is associated with grid-size selection for mesoscale models. The monotonicity of grid size is investigated, and it is strictly proved that grid size increases with increasing fitting exponent, indicating that the universal grid size is determined by the minimum fitting exponent. An example of landslide-prone areas in western Sichuan is given, and the universal grid spacing of 4.1 km is shown to be a requirement to resolve 90% of terrain height variance for mesoscale models, without resorting to the parameterization of subgrid-scale terrain variance. Comparison among results of different simulations shows that the simulations estimate the observed precipitation well when using a resolution of 4.1 km or finer. Although the main flow patterns are similar, finer grids produce more complex patterns that show divergence zones, convergence zones and vortices.Horizontal grid size significantly affects the vertical structure of the convective boundary layer. Stronger vertical wind components are simulated for finer grid resolutions. In particular, noticeable sinking airflows over mountains are captured for those model configurations. 相似文献
19.
Large-eddy simulation (LES) of a stable atmospheric boundary layer is performed using recently developed dynamic subgrid-scale
(SGS) models. These models not only calculate the Smagorinsky coefficient and SGS Prandtl number dynamically based on the
smallest resolved motions in the flow, they also allow for scale dependence of those coefficients. This dynamic calculation
requires statistical averaging for numerical stability. Here, we evaluate three commonly used averaging schemes in stable
atmospheric boundary-layer simulations: averaging over horizontal planes, over adjacent grid points, and following fluid particle
trajectories. Particular attention is focused on assessing the effect of the different averaging methods on resolved flow
statistics and SGS model coefficients. Our results indicate that averaging schemes that allow the coefficients to fluctuate
locally give results that are in better agreement with boundary-layer similarity theory and previous LES studies. Even among
models that are local, the averaging method is found to affect model coefficient probability density function distributions
and turbulent spectra of the resolved velocity and temperature fields. Overall, averaging along fluid pathlines is found to
produce the best combination of self consistent model coefficients, first- and second-order flow statistics and insensitivity
to grid resolution. 相似文献
20.
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. 相似文献