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1、Roughness and Wind Shear粗糙度和风切变High above ground level, at a height of about 1 kilometer, the wind is hardly influenced by the surface of the earth at all. In the lower layers of the atmosphere, however, wind speeds are affected by the friction against the surface of the earth. In the wind industry
2、one distinguishes between the roughness of the terrain, the influence from obstacles, and the influence from the terrain contours, which is also called the orography of the area. We shall be dealing with orography, when we investigate so called speed up effects, i.e. tunnel effects and hill effects,
3、 later.在距离地面约 1 公里的高度，风几乎不受地球表面的影响。然而，在大气的下层，风速 受到与地球表面的摩擦的影响。在风能行业中，人们区分地形的粗糙度，障碍物的影响 以及地形轮廓的影响，这也称为该地区的地形。当我们稍后研究所谓的加速效应，即隧 道效应和山地效应时，我们将讨论山岳学Orography。Roughness 粗糙度In general, the more pronounced the roughness of the earths surface, the more the wind will be slowed down.一般来说，地球表面粗糙度越明显，风速就越慢。Fore
4、sts and large cities obviously slow the wind down considerably, while concrete runways in airports will only slow the wind down a little. Water surfaces are even smoother than concrete runways, and will have even less influence on the wind, while long grass and shrubs and bushes will slow the wind d
5、own considerably.森林和大城市会显著减缓了风速，而机场的混凝土跑道减缓风速的效果有限。水面比混 凝土跑道更平滑，对风的影响更小，而长草，灌木则会使风速大幅减缓。Roughness Classes and Roughness Lengths 粗糙度等级和粗糙度长度 粗糙度等级和粗糙度长度的正确定义可在参考手册中找到。术语粗糙度长度实际上是地 面以上的距离，其中风速理论上应该为零。In the wind industry, people usually refer to roughness classes or roughness lengths, when they evalua
6、te wind conditions in a landscape. A high roughness class of 3 to 4 refers to landscapes with many trees and buildings, while a sea surface is in roughness class 0.在风能行业中，人们通常会在评估风况时参考粗糙度等级(roughness classes )或粗糙度长度( roughness lengths)。 具有许多树木和建筑物的场地一般是3 至 4的高粗糙度等级，而海面的粗糙度等级为 0。Concrete runways in a
7、irports are in roughness class 0.5. The same applies to the flat, open landscape to the left which has been grazed by sheep.机场的混凝土跑道的粗糙度等级为 0.5。这同样适用于由绵羊放牧的平坦，开阔的场地(如下图所示)。Sheep are a wind turbines best friend. In this picture from Akaroa Spit, New Zealand, the sheep keep the roughness of the landsc
8、ape down through their grazing.绵羊是风力涡轮机最好的朋友。在这张来自新西兰Akaroa Spit的照片中，通过放牧保持 了场地的低粗糙度。The proper definition of roughness classes and roughness lengths may be found in the Reference Manual. The term roughness length is really the distance above ground level where the wind speed theoretically should be
9、 zero.粗糙度等级和粗糙度长度的正确定义可在参考手册中找到。术语粗糙度长度实际上是地面以上的距离，其中风速理论上应该为零。Wind Shear 风切变This graph was plotted with the wind speed calculator on the next page. It shows you how wind speeds vary in roughness class 2 (agricultural land with some houses and sheltering hedgerows with some 500 m intervals), if we a
10、ssume that the wind is blowing at 10 m/s at a height of 100 metres.该图使用下一章节的风速计算器绘制。它向您展示了如果我们假设高度 100 米处风速10 米/秒，那么风速如何在粗糙度等级2(有一些间隔约500 米的房屋和篱笆的农田) 中变化。The fact that the wind profile is twisted towards a lower speed as we move closer to ground level, is usually called wind shear. Wind shear may al
11、so be important when designing wind turbines. If you consider a wind turbine with a hub height of 40 metres and a rotor diameter of 40 metres, you will notice that the wind is blowing at 9.3 m/s when the tip of the blade is in its uppermost position, and only 7.7 m/s when the tip is in the bottom position. This means that the forces acting on the rotor blade when it is in its top position are far larger than when it is in its bottom position.当靠近地面时风向较低速度扭曲，这通常被称为风切变。在设计风机时，风切变也很重 要。如果你考虑一个轮毂高度为40 米，转子直径为40 米的风机，你会注意到当叶片尖端处于最高位置时风速为9.3米/秒，而当尖端处于底部位置时只有7.7 米/ s。这意味着当转子叶片处于其顶部位置时作用在转子叶片上
