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1.
风电场流场特性及风机布局数值模拟研究 总被引：1，自引：0，他引：1
针对风电场流场特性研究对风力机工作性能提高的重要意义,采用计算流体力学（CFD）方法在单机风力机模拟验证的基础上,对某风电场单风力机和三种布局条件下的风电场流场特性进行了数值模拟研究。考察了不同布局条件下风电场速度、叶轮表面压力以及湍流涡的分布特性。结果表明：叶轮后方尾流效应明显,速度损失随着相对距离的增加而逐渐减小,风力机处中心尾流速度比率最低降为0.4;当相对距离超过4 d后,风速可恢复为初始速度的90%以上;尾流速度与涡流粘性呈负相关性;三风力机平行布置时,各风力机尾流速度比率基本一致;三风机组在错落布置时,尾流效应对下游风力机工作性能影响较小,错落角度越大,尾流损失越小。 相似文献
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3.
条件不稳定大气中二维小尺度双脊地形上空对流及降水特征 总被引：3，自引：1，他引：2
在条件不稳定大气条件下,二维小尺度双脊钟形地形上空对流触发、传播和降水分布特征主要决定于地形上游基流强度、双脊地形配置形式、地形高度及其山谷宽度。双脊地形在沿基流方向上有两种配置:高脊地形位于上游和低脊地形位于上游。对于高脊地形位于上游的双脊地形,上游高地形将起主导作用,山地上空对流及降水特征与单脊地形类似。对于低脊地形位于上游的双脊地形,上游低地形可明显地改变下游高地形的前方来流,同时,下游高地形也能够对上游低地形背风侧流动产生影响,从而导致出现地形上空复杂的对流传播、降水分布特征。对于低脊地形位于上游的双脊地形,其山谷宽度主要决定了双脊地形与单脊地形之间在对流、降水分布等的差异;当山谷宽度较小时,双脊地形可以近似为一个包络地形,此时地形上空的对流、降水特征与单脊地形类似;当山谷宽度较大时,双脊上空流动相互影响较小,此时双脊地形可以分成两个单脊地形;当山谷宽度在一定范围内,其上空的对流及其降水分布与单脊地形有明显差异。对于低脊地形位于上游、中等山谷宽度的双脊地形上空降水主要呈现4种类型:(1)山谷与低脊迎风坡降水;(2)高脊迎风坡降水;(3)低脊山峰与高脊迎风坡降水;(4)低脊背风侧、双脊山峰准静止降水。 相似文献
4.
在分析博尔塔拉河水文特征的基础上,对水化学进行了系统的分析,研究结果表明:博尔塔拉河的矿化度和总硬度等主要离子含量沿程均有不同程度的增加,上游到中游增幅不大,中游到下游开始呈直线上升,下游矿化度和总硬度分别超过1000mg/L和250mg/L,主要离子含量也增加明显,其变化特征与矿化度基本一致。上中游河段阴离子中以HCO3-占优势,阳离子中以Ca2 为主;下游河段阴离子中以SO42-占优势,阳离子中以Na 为主。水化学类型由上游向下游过渡变化的分带特征:从上游、中游到下游河水水化学特征依次主要表现为HCO3-型、HCO3-—SO42-型和SO42-型。 相似文献
5.
在不同的环境风场作用下台风移动路径出现差异,导致海洋冷尾流呈现不同的响应特征,从而对台风强度产生影响。利用海气耦合模式进行理想试验,模拟研究了在均匀的东、西风场条件下冷尾流的响应特征,以分析台风强度出现差异的原因。研究结果表明,在均匀的东风环境场与β效应的共同作用下,台风路径呈西北方向移动,冷尾流沿台风路径呈非对称分布,右侧降温幅度大于左侧,并持续影响台风内核海气界面热通量的输送。而均匀的西风环境场抵御了部分β效应,使得台风东移北抬,当强度增强到一定程度后向西北方向移动,最大幅度的冷尾流出现在台风南侧,眼区热通量的输送受冷尾流影响较小。另外,在台风快速加强阶段,眼区范围内的潜热通量输送对台风加强更为关键。 相似文献
6.
1.前言使用最普遍的风速测量仪器是皮托静压管,但它在低风速中得到的压差变小,分辨率变低(例如1m/s时,0.6mm水柱{0.5％Pa})。热线风速计即使在低风速中,灵敏度也很高。不足的是,它不是测风速的绝对值,需要用几种方法订正。本文介绍小于1m/s的风速的有关测量理论及实验研究结果。从确立低风速基准测量法的角度来说,这种测量法最好采用绝对测量法。一种考虑是从流体内温度的空间变化为标记求出其移动速度。迄今一直在研究的热尾流法和脉冲线法,都是出于同样的思路。这两种方法都在气流方向设置两根金属丝。用电加热的办法给上游的金属丝加热,则流过此金属丝的空气也就被加热。当热空气向下游移动时,作为检出温度用的位于下游的金属丝随空气 相似文献
7.
利用FY-4A卫星等资料分析了2019—2021年的19次庐山白天云海过程（12个传统云海和7个瀑布云过程）,研究了庐山云海特征及其形成机制,评估了卫星资料在云海识别中的应用。研究表明：FY-4A可见光云图可基本辨识庐山云海范围及宏观演变特征,但较难刻画出小尺度瀑布云的精细结构;FY-4A的云顶高度L2产品可用于庐山传统云海的识别,但较难识别瀑布云过程。非洋面海岛的庐山也存在云系尾流现象且频率较高（共3次过程）,由绕流作用形成的尾流云系呈逗号状分布,做规律性摆动但无连续涡旋;该尾流型云海形成的主要因素是庐山为相对周边孤立的椭圆形山体、冷高压底部的强北风低空急流、山腰逆温层。庐山云海发生时大多受地面高压控制且位于850 hPa的高湿区或边缘区域,该区域的弱下沉运动形成的逆温层和低空充沛的水汽有利于庐山云海形成及维持。 相似文献
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利用1961-2016年大渡河流域15个气象站逐日降水资料,采用算术平均法计算上、中、下游三个分段流域的面雨量,对其时空分布特征进行分析,计算流域内雨季开始及结束期。结果表明:(1)大渡河中、上游面雨量呈上升趋势,下游呈下降趋势,下游年降水量相对变率和极差最大,其次是中游,上游最小;夏季流域面雨量最大,占全年降水的50%~60%。5-9月流域面雨量在100~200 mm之间,11月至翌年2月在5~20 mm之间,流域内面雨量峰值出现时间由北向南延迟,上、中、下游相差近1个月。(2)依据雨季转换指标计算出的雨季开始及结束期比依据强降水计算的更稳定,大渡河流域下游进入雨季最早,其次是中游,上游最晚,而上游雨季结束最早,其次是中游,下游最晚,上、中、下游雨季持续时间分别为172 d、182 d和195 d。(3)当上游出现强降水时,中、下游很少同时出现强降水,当下游出现强降水时,中游经常同时也出现强降水。 相似文献
9.
综合分析人工触发闪电通道底部的电流数据和电场变化数据,获得对M分量的新认识。M分量的幅值、上升时间、半峰值宽度、转移电荷量的几何平均值分别为301 A,341 μs,662 μs,0.207 C。但发现有两种类型的M分量,其统计特征和分布特征均体现了较大差别。第1类M分量幅度较小,半峰值宽度较大,上升时间较长;第2类M分量则幅度较大,半峰值宽度较小,上升时间较短,两类M分量和回击的时间间隔有较大差异。采用双波放电模型,通过设定不同入射电流波速度和反射电流波速度,对两类M分量进行从电流到电场的反演。结果表明:当模拟电场和测量电场比较一致时,第1类M分量的入射速度和反射速度的比值大于第2类M分量,即两类M分量的放电机制具有一定差异。 相似文献
10.
热带气旋(TC)在向高纬度地区移动过程中往往会转变为温带气旋,称之为温带变性(ET)过程。ET过程涉及到热带系统与中纬度环流的复杂相互作用,并对局地系统直至大范围环流均产生影响,这种影响甚至向下游延伸到半球的尺度。由于ET过程及其下游影响给中纬度地区带来严重灾害性天气,而对其的预报一直是一个难题,因而关于此问题的科学研究和业务预报是近年来国际上的一个热点,国内的有关工作也已开展。从TC在ET过程中与中纬度环流的相互作用、ET过程对中纬度下游环流的影响和ET过程及其下游影响的数值预报三个方面总结和分析了近年来国内外的有关研究进展,为国内学术界进一步开展相关研究提供参考。主要进展包括:(1) TC高层出流输出低位涡(PV)空气改变温带上层结构以及TC环流直接作用于中纬度流是TC-中纬度流相互作用的主要方式;TC相对于上游槽的位置对ET过程及其下游影响很关键;各种物理过程在相互作用中起到不同的作用;(2) TC所激发的Rossby波在与急流相联系的上层PV梯度上向下游频散是下游发展的主要方式;下游发展具有显著的边界俘获和上下层耦合发展的特征;(3) 目标观测、集合预报和变分同化等技术的发展提高了ET及其下游影响的数值预报水平。 相似文献
11.
北京325 m气象塔塔体对测风影响的数值模拟 总被引：1，自引：0，他引：1
安装在气象观测塔上的仪器进行风速测量时,气象塔塔体本身会对流场有一定的影响,使其附近局部流场发生变化,产生绕流和尾流,导致所测风场数据相对于真实风场值失真,利用计算流体力学软件Fluent对北京325m框架式气象塔周围的风场进行了模拟,给出流向风速在该塔伸臂上测风位置的失真情况,及风速失真大小随风向风速的变化规律,计算表明若伸臂处于迎风面,在测风点上的风速误差均小于5%,与实际观测一致,验证了北京325m气象塔风速伸臂设计的合理性。 相似文献
12.
We use the Wind Farm Parameterization(WFP) scheme coupled with the Weather Research and Forecasting model under multiple resolution regimes to simulate turbulent wake dynamics generated by a real onshore wind farm and their influence at the local meteorological scale. The model outputs are compared with earlier modeling and observation studies. It is found that higher vertical and horizontal resolutions have great impacts on the simulated wake flow dynamics. The corresponding wind speed deficit and turbulent kinetic energy results match well with previous studies. In addition, the effect of horizontal resolution on near-surface meteorology is significantly higher than that of vertical resolution. The wake flow field extends from the start of the wind farm to downstream within 10 km, where the wind speed deficit may exceed 4%. For a height of 150 m or at a distance of about 25 km downstream, the wind speed deficit is around 2%. This indicates that, at a distance of more than 25 km downstream, the impact of the wind turbines can be ignored. Analysis of near-surface meteorology indicates a night and early morning warming near the surface, and increase in near-surface water vapor mixing ratio with decreasing surface sensible and latent heat fluxes. During daytime, a slight cooling near the surface and decrease in the near-surface water vapor mixing ratio with increasing surface sensible and latent heat fluxes is noticed over the wind farm area. 相似文献
13.
为了提高风电场风速预报和功率预测的精度和准确率,并考虑风机测风数据的不稳定因素,以多年服务的内蒙古中部某风力发电场A为研究区,在勘察风电场地形及风机布局后,按照季节、风向进行风机间风速时空相关性分析,划分出风机轮毂高度风速高相关为典型特征的风机网格分类片区,采用卡尔曼滤波方法,通过直接和间接两种订正方案,分别进行风机片区风速订正。结果表明:风速高相关风机片区的划分,对于提高风电场风速预报及功率预测精度和准确率具有一定作用,利用风电场区测风塔梯度观测风速,对风机片区进行间接订正,可有效改善数值模式预报风速,15个片区类型下相关系数由0.18~0.72提高至0.67~0.91,误差绝对值由1.6~2.9 m·s-1降低至1.0~1.5 m·s-1。 相似文献
14.
Kapil Varshney 《Theoretical and Applied Climatology》2013,111(3-4):427-435
Helical tip vortices in the wake of a wind turbine have been investigated in this study. To elucidate the near-wake flow field of the wind turbine, the wake has been explored in the Reynolds number (Re) range 1000 ≤?Re?≤?5000 using qualitative dye flow visualization and quantitative digital particle-image velocimetry techniques. Flow visualization showed the dye getting trapped in the shape of spirals surrounding the helical vortex cores. It was found that the helical vortex core size was increasing with downstream distance. It was also found that the normalized stream-wise component of the wake velocity decreased with increasing tip-speed ratios. The results indicate that vorticity peaks at the center of the core and it decays as the vortex moves downstream, showing that the viscous dissipation is active even at length scales of approximately 5 diameters. 相似文献
15.
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. 相似文献
16.
A Wind-Tunnel Investigation of Wind-Turbine Wakes: Boundary-Layer Turbulence Effects 总被引：1，自引：1，他引：0
Wind-tunnel experiments were performed to study turbulence in the wake of a model wind turbine placed in a boundary layer
developed over rough and smooth surfaces. Hot-wire anemometry was used to characterize the cross-sectional distribution of
mean velocity, turbulence intensity and kinematic shear stress at different locations downwind of the turbine for both surface
roughness cases. Special emphasis was placed on the spatial distribution of the velocity deficit and the turbulence intensity,
which are important factors affecting turbine power generation and fatigue loads in wind energy parks. Non-axisymmetric behaviour
of the wake is observed over both roughness types in response to the non-uniform incoming boundary-layer flow and the effect
of the surface. Nonetheless, the velocity deficit with respect to the incoming velocity profile is nearly axisymmetric, except
near the ground in the far wake where the wake interacts with the surface. It is found that the wind turbine induces a large
enhancement of turbulence levels (positive added turbulence intensity) in the upper part of the wake. This is due to the effect
of relatively large velocity fluctuations associated with helicoidal tip vortices near the wake edge, where the mean shear
is strong. In the lower part of the wake, the mean shear and turbulence intensity are reduced with respect to the incoming
flow. The non-axisymmetry of the turbulence intensity distribution of the wake is found to be stronger over the rough surface,
where the incoming flow is less uniform at the turbine level. In the far wake the added turbulent intensity, its positive
and negative contributions and its local maximum decay as a power law of downwind distance (with an exponent ranging from
−0.3 to −0.5 for the rough surface, and with a wider variation for the smooth surface). Nevertheless, the effect of the turbine
on the velocity defect and added turbulence intensity is not negligible even in the very far wake, at a distance of fifteen
times the rotor diameter. 相似文献
17.
Effects of Thermal Stability and Incoming Boundary-Layer Flow Characteristics on Wind-Turbine Wakes: A Wind-Tunnel Study 总被引：2，自引：1，他引：1
Wind-tunnel experiments were carried out to study turbulence statistics in the wake of a model wind turbine placed in a boundary-layer
flow under both neutral and stably stratified conditions. High-resolution velocity and temperature measurements, obtained
using a customized triple wire (cross-wire and cold wire) anemometer, were used to characterize the mean velocity, turbulence
intensity, turbulent fluxes, and spectra at different locations in the wake. The effect of the wake on the turbulence statistics
is found to extend as far as 20 rotor diameters downwind of the turbine. The velocity deficit has a nearly axisymmetric shape,
which can be approximated by a Gaussian distribution and a power-law decay with distance. This decay in the near-wake region
is found to be faster in the stable case. Turbulence intensity distribution is clearly non-axisymmetric due to the non-uniform
distribution of the incoming velocity in the boundary layer. In the neutral case, the maximum turbulence intensity is located
above the hub height, around the rotor tip location and at a distance of about 4–5.5 rotor diameters, which are common separations
between wind turbines in wind farms. The enhancement of turbulence intensity is associated with strong shear and turbulent
kinetic energy production in that region. In the stable case, the stronger shear in the incoming flow leads to a slightly
stronger and larger region of enhanced turbulence intensity, which extends between 3 and 6 rotor diameters downwind of the
turbine location. Power spectra of the streamwise and vertical velocities show a strong signature of the turbine blade tip
vortices at the top tip height up to a distance of about 1–2 rotor diameters. This spectral signature is stronger in the vertical
velocity component. At longer downwind distances, tip vortices are not evident and the von Kármán formulation agrees well
with the measured velocity spectra. 相似文献
18.
We examine the influence of a modern multi-megawatt wind turbine on wind and turbulence profiles three rotor diameters ( $D$ D ) downwind of the turbine. Light detection and ranging (lidar) wind-profile observations were collected during summer 2011 in an operating wind farm in central Iowa at 20-m vertical intervals from 40 to 220 m above the surface. After a calibration period during which two lidars were operated next to each other, one lidar was located approximately $2D$ 2 D directly south of a wind turbine; the other lidar was moved approximately $3D$ 3 D north of the same wind turbine. Data from the two lidars during southerly flow conditions enabled the simultaneous capture of inflow and wake conditions. The inflow wind and turbulence profiles exhibit strong variability with atmospheric stability: daytime profiles are well-mixed with little shear and strong turbulence, while nighttime profiles exhibit minimal turbulence and considerable shear across the rotor disk region and above. Consistent with the observations available from other studies and with wind-tunnel and large-eddy simulation studies, measurable reductions in wake wind-speeds occur at heights spanning the wind turbine rotor (43–117 m), and turbulent quantities increase in the wake. In generalizing these results as a function of inflow wind speed, we find the wind-speed deficit in the wake is largest at hub height or just above, and the maximum deficit occurs when wind speeds are below the rated speed for the turbine. Similarly, the maximum enhancement of turbulence kinetic energy and turbulence intensity occurs at hub height, although observations at the top of the rotor disk do not allow assessment of turbulence in that region. The wind shear below turbine hub height (quantified here with the power-law coefficient) is found to be a useful parameter to identify whether a downwind lidar observes turbine wake or free-flow conditions. These field observations provide data for validating turbine-wake models and wind-tunnel observations, and for guiding assessments of the impacts of wakes on surface turbulent fluxes or surface temperatures downwind of turbines. 相似文献
19.
Impact of the Diurnal Cycle of the Atmospheric Boundary Layer on Wind-Turbine Wakes: A Numerical Modelling Study 总被引：1，自引：1，他引：0
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