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1.
We evaluate the Reynolds-averaged Navier–Stokes equations available as commercial computational fluid dynamics code for the
simulation of a neutral atmospheric boundary layer and attempt to define a proper numerical simulation procedure. Four turbulence
models, including two-equation and Reynolds stress models, were evaluated together with two near-wall models. Mesh and map
digitization sensitivity tests were also performed. The simulations were compared to experimental field data from the Askervein
Hill in Scotland. The results show that the simulations performed with ANSYS CFX 12.1 on a proper mesh and topological map
with a Reynolds stress turbulence model provided the best wind-speed predictions when compared to the experimental results. 相似文献
2.
Several two-equation turbulence models using isotropic eddy viscosity and wall functions are assessed by solution of the neutral atmospheric boundary layer over a flat surface and wind flow over two- and three-dimensional models and real terrain. Calculations are presented for wind flow over the Sirhowy Valley in Wales, an embankment along the Rhine in Germany and the Askervein Hill in Scotland. Comparisons of predictions with previous work, and laboratory and field data, show that the RNG-based k– model gives the best agreement with respect to the flow profiles and length of the separated flow region. The results of this model are analyzed with a non-linear stress-strain relation to gauge the potential effect of turbulence anisotropy. 相似文献
3.
We present an immersed-boundary method to simulate high-Reynolds-number turbulent flow over the complex terrain of Askervein and Bolund Hills under neutrally-stratified conditions. We reconstruct both the velocity and the eddy-viscosity fields in the terrain-normal direction to produce turbulent stresses as would be expected from the application of a surface-parametrization scheme based on Monin–Obukhov similarity theory. We find that it is essential to be consistent in the underlying assumptions for the velocity reconstruction and the eddy-viscosity relation to produce good results. To this end, we reconstruct the tangential component of the velocity field using a logarithmic velocity profile and adopt the mixing-length model in the near-surface turbulence model. We use a linear interpolation to reconstruct the normal component of the velocity to enforce the impermeability condition. Our approach works well for both the Askervein and Bolund Hills when the flow is attached to the surface, but shows slight disagreement in regions of flow recirculation, despite capturing the flow reversal. 相似文献
4.
A three-dimensional nonlinear numerical model, that has been extensively used previously to predict environmental water flows, was applied to predict the flow over an isolated hill, Askervein. Predictions are reported for winds approaching the hill from 210 ° and 180 ° clockwise from north, both under almost neutral atmospheric conditions.The model predictions were compared with data collected during a major field study in 1983. From the comparisons it was concluded that the model predicts the mean flow variables with good accuracy. Larger discrepancies were found for quantities related to the turbulence, pointing to deficiencies in the turbulence model, and perhaps in some of the measurements. 相似文献
5.
R. E. Mickle N. J. Cook A. M. Hoff N. O. Jensen J. R. Salmon P. A. Taylor G. Tetzlaff H. W. Teunissen 《Boundary-Layer Meteorology》1988,43(1-2):143-169
This is one of a series of papers on the Askervein Hill Project. It presents results from the Askervein 1982 and 1983 experiments
in the form of vertical profiles of mean wind and turbulence integral statistics at upwind reference locations and at two
hilltop sites. The data were obtained from a variety of sensors including sonic, Gill UVW and cup anemometers mounted on 50,
30, 17 and 10 m towers and TALA kite systems. Comparisons with numerical-model predictions are discussed. 相似文献
6.
The Askervein Hill project was a collaborative study of boundary-layer flow over low hills carried out under the auspices of the International Energy Agency Programme of R & D on Wind Energy Conversion Systems. Two field experiments were conducted during September-October 1982 and 1983 on and around Askervein, a 116 m high hill on the west coast of the island of South Uist in the Outer Hebrides of Scotland. During the experiments, over 50 towers were deployed and instrumented for wind measurements. The majority were simple 10 m posts bearing cup anemometers but, in the 1983 study, two 50 m towers, a 30 m tower, a 16 m tower, and thirteen 10 m towers were instrumented for 3-component turbulence measurement.The present paper provides an overview of the project as a whole, including details of the instrumentation and a summary of the data obtained. Additional papers in the series, which are to appear in this journal, will consider different aspects of the experimental data and related numerical-model and wind-tunnel studies.
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7.
Large-eddy simulations of the neutrally stratified flow over the Askervein Hill were performed, to improve the knowledge of
the flow obtained from field measurements and numerical simulations with Reynolds averaged Navier-Stokes (RANS) methods. A
Lagrangian dynamic subgrid model was used but, to avoid the underdissipative character near the ground, it was merged with
a damped Smagorinsky model. Simulations of a flat boundary-layer flow with this subgrid model showed that the turbulent vertical
motions and shear stress were better resolved using grids with a stream to spanwise aspect ratio Δx / Δy = 2 than with an aspect ratio Δx / Δy = 1. Regarding the flow over the Askervein Hill, it was found that large-eddy simulations provide an acceptable solution
for the mean-velocity field and better predictions of the turbulent kinetic energy in the upstream side of the hill than the
model. However, as with the model, grid convergence was not achieved in the lee side and the size of the zone with reversed flow increased with the grid
refinement. Nevertheless, the existence of the intermittent separation predicted with unsteady RANS in part one of this work
seems unquestionable, due to the deceleration of the flow. In our opinion, a better modelling of the decelerating boundary
layer in the lee side is required to improve the results obtained using equilibrium assumptions and achieve grid convergence. 相似文献
8.
The flow solver “3DWind” is used to explore new aspects of the Askervein hill flow case. Previous work has investigated sensitivities to the grid, the inflow boundary profile, the roughness and the turbulence model. Several different linear and non-linear numerical models have also been validated by means of the Askervein hill case. This analysis focuses on the flow sensitivity to the grid spacing, the incident wind direction and the vertical resolution of topographic data. The horizontal resolution is found to be fine enough to cause only minor differences compared to a grid where every second node is removed. The vertical resolution dependence is mainly attributed to the wall functions. Simulations are performed for wind directions 200°, 205°, 210° and 215° at the reference station. The smallest directional biases compared to experimental values along a line through the hilltop are found for the directions 200° and 205°. There are larger wind direction changes along this line through the hilltop in the 200° case than in the 215° case. Still the simulation results give less veering than found in the experimental results, and this is maybe caused by a slightly stable atmosphere. The sensitivity to the vertical resolution of the topographical data is found to be particularly high close to the ground at the top of the hill; this is where the speed-up is most important. Differences decrease with the height from the ground. At higher levels the speed-ups are smaller and caused by terrain formations with larger scales. 相似文献
9.
10.
The neutrally stratified flow over the Askervein Hill was simulatedusing a terrain-following coordinatesystem and a two-equation(k - ) turbulence model. Calculations were performed on awide range of numerical grids to assess, among other things, theimportance of spatial discretization and the limitations of theturbulence model. Our results showed that a relatively coarse gridwas enough to resolve the flow in the upstream region of the hill;at the hilltop, 10 m above the ground, the speed-up was 10% lessthan the experimental value. The flow's most prominent feature wasa recirculating region in the lee of the hill, which determinedthe main characteristics of the whole downstream flow. This regionhad an intermittent nature and could be fully captured only in the caseof a time-dependent formulation and a third-order discretization ofthe advective terms. The reduction of the characteristic roughnessnear the top of the hill was also taken into account, showing theimportance of this parameter, particularly in the flow close to theground at the summit and in the downstream side of the hill.Calculations involving an enlarged area around the Askervein Hillshowed that the presence of the nearby topography affected the flowneither at the top nor downstream of the Askervein Hill. 相似文献
11.
H. W. Teunissen M. E. Shokr A. J. Bowen C. J. Wood D. W. R. Green 《Boundary-Layer Meteorology》1987,40(1-2):1-29
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. 相似文献
12.
Measurements of flow over an elongated ridge and its thermal stability dependence: The mean field 总被引：1，自引：0，他引：1
Measurements of mean wind flow and turbulence parameters have been made over Cooper's Ridge, a 115 m high elongated ridge with low surface roughness. This paper describes measurements of the streamwise and vertical variations in the mean field for a variety of atmospheric stability conditions. In near-neutral conditions, the normalised speedup over the ridge compares well with measurements from Askervein (Mickleet al., 1988). The near-neutral results are also compared to an analytical flow model based on that of Huntet al. (1988a). Measured streamwise variations show less deceleration at the foot of the hill and slightly more acceleration at the crest of the hill than does the model. In non-neutral conditions, the speedup over the ridge reduces slightly in unstable conditions and increases by up to a factor of two in stable conditions. The model is modified to allow boundary-layer stability to change the upwind wind profile and the depths of the inner and middle layers. Such a modification is shown to describe the observations of speedup well in unstable and weakly stable conditions but to overestimate the speedup in moderate to strongly stable conditions. This disagreement can be traced to the model's overestimation of the upstream scaling velocity at the height of the middle layer through its use of a stable wind profile form which has greater shear than that of the observed profiles, in possible combination with the three-dimensionality of the ridge which would allow enhanced flow around, rather than over, the feature in more stable conditions. 相似文献
13.
J. R. Salmon A. J. Bowen A. M. Hoff R. Johnson R. E. Mickle P. A. Taylor G. Tetzlaff J. L. Walmsley 《Boundary-Layer Meteorology》1988,43(3):247-271
This is one of a series of papers on the Askervein Hill Project. It presents results on the variations in mean wind speed at fixed heights (z) above the ground from linear arrays of anemometer posts and towers. Most of the data are for z = 10 m but some are for z = 3 m. Selected and directionally grouped data from the 55 Mean Flow runs are presented together with mean flow data from Askervein '83 Turbulence runs. Comparisons are made between the data and guideline estimates of fractional speed-up ratio at hilltop locations and between the data and MS3DJH/3 model predictions along the tower lines. There is good agreement in most cases. 相似文献
14.
15.
Mikhail Novitsky Danny D. Reible Bernardo M. Corripio 《Boundary-Layer Meteorology》1992,59(1-2):163-175
Conventional atmospheric dispersion and air quality models require that the wind field be known with a higher resolution than is currently available from field monitoring stations in most coastal areas. In this paper, a numerical model is developed to predict the wind flow field during the land-sea breeze. The form and assumptions and method of solution of the model are described. The model output is compared to atmospheric data taken from a field study conducted in the Santa Barbara Channel and Ventura-Oxnard plain in southern California. 相似文献
16.
The study of human dimensions of global climatic change is still in the initial stage of development. Several attempts have been undertaken to define sensible research strategies in the field but until now relatively little empirical work has been undertaken and there is a lack of sound theoretical arguments. The present paper presents a theory-based empirical study of determinants influencing the probability that somebody takes climate-relevant environmental action. Important methodological differences between current models of climate dynamics and models of human reality are discussed in order to build three models of climate-related environmental action. A model focussed on the information transfer from science to the public at large is compared with a model focussed on sociodemographic characteristics and with a model focussed on socio-cultural variables like interpersonal rules and social networks. The hypothesis that the latter model is strongly superior to the former ones is tested and confirmed. Some implications for interdisciplinary cooperation and for policy making are discussed. 相似文献
17.
第I部分研究结果(徐枝芳等,2007)表明模式与实际观测站地形高度差异对地面观测资料同化效果有较大影响。此文在MM5_3DVAR同化系统中利用近地层相似理论将地面观测资料进行直接三维变分同化分析,考虑模式与实际观测站地形高度差异对同化效果的影响,提出在地面观测误差中增加地形代表性误差来解决这个问题。研究结果表明:地面资料同化分析时,在其观测误差中加入一项新的误差——地形代表性误差,能较好地解决地面资料同化分析中模式与观测站地形高度差异问题;地面资料参与同化分析,在观测误差中加入与模式和实际观测站地形高度差异大小相关的地形代表性误差时,地面观测值对分析值的影响随着地形高度差异代表性误差的加入而减小,同时又部分地将地面观测信息通过变分分析融进分析场,使得低层分析更接近真实场,且地面资料利用率更高,24小时降水数值预报(模拟)的效果较好。 相似文献
18.
A. F. Voevodin V. S. Nikiforovskaya V. V. Ostapenko 《Russian Meteorology and Hydrology》2008,33(3):193-198
Two mathematical models based on the Saint-Venant equations are considered for calculating unsteady flows in stream channels with floodplains. In model 1, the influence of floodplain on the release or flood wave travelling is taken into account through the total morphological and hydraulic characteristics of stream channel and floodplain. In model 2, based on singling out a fluvial flow, the floodplain plays a role of an accumulation capacity. To study the field of a practical applicability of the proposed models, comparative calculations have been carried out with a two-dimensional (plan) model. The analysis of results demonstrated a sufficient efficiency of models 1 and 2 with allowance for floodplains in meandering stream channels. Due to a less laborious preparation of initial data, model 2 is more preferable. 相似文献
19.
Beljaars et al. (1987) developed a model for neutrally stratified boundary-layer flow over roughness changes and topography. It has been discovered that a constant parameter, , was missing in the algebraic-stress closure equations of their paper. This omission also occurred in the MSFD model code but only affects the Askervein Hill shear-stress results for the E-- turbulence closure in Beljaars et al. It also changes the stress results of Karpik (1988), but not his conclusions regarding the robustness of his improved numerical scheme. The present paper demonstrates the effect of the omission of the parameter, , and tests the sensitivity of the model to variations in its value. The new results are compared with the data and model results of Zeman and Jensen (1987). 相似文献
20.
开发了适合城市环境下的应急重气扩散模型——SLAB_URBAN模型,该模型能够对城市环境下重气的传输扩散过程进行模拟。模型的原理基于重气扩散浅层理论,采用了新的城市边界层和扩散参数的参数化方案。该方案考虑了城市冠层内特有的风和湍流扩散的特征,能够体现城市边界层和湍流对重气扩散的影响。对美国盐湖城Urban2000的城市扩散试验进行模拟,主要验证下风方向观测弧所观测到的气体最大小时平均浓度与源释放速率的比值。结果表明,模型能够比较好地模拟出下风方向上浓度的分布特征。另外,与国外同类城市扩散模型的比较来看,SLAB_URBAN模型的模拟能力居于前列。 相似文献