2022-03-10 21:54:11
  • The role of wind tunnels

7.1 Introduction

Most practising structural engineers will not themselves operate wind tunnels, but they may be clients of wind tunnel groups who will provide wind loading information for new or existing structures, usually by means of model tests. For this reason, this chapter will not attempt to describe wind tunnel techniques in detail. There are detailed references, guide books and manuals of practice available which perform this function (e.g. Cermak, 1977; Reinhold, 1982; Australasian Wind Engineering Society, 2001; American Society of Civil Engineers, 1999). However sufficient detail is given here to enable the educated client to be able to lsquo;ask the right questionsrsquo; of their wind tunnel contractors.

In the following sections, a brief description of wind tunnel layouts is given, and methods of simulation of natural wind flow and experimental measurement techniques are discussed.

7.2 Wind tunnel layouts

7.2.1 Historical

The first use of a wind tunnel to measure wind forces on buildings is believed to have been made by Kernot in Melbourne, Australia (1893). A sketch of the apparatus, which he called a lsquo;blowing machinersquo;, is given in Figure 7.1 (Aynsley et al., 1977). This would now be described as an lsquo;open-circuit, open test-sectionrsquo; arrangement. With this equipment, Kernot studied wind forces on a variety of bluff bodies – cubes, pyramids, cylinders, etc., and on roofs of various pitches.

Figure 7.1 Sketch of W. C. Kernotrsquo;s lsquo;blowing machinersquo; of 1893 (Aynsley et al., 1977).

140 The role of wind tunnels

Figure 7.2 Layout of an open-circuit wind tunnel.

At about the same time, Irminger (1894) in Copenhagen, Denmark used the flow in a flue of a chimney to study wind pressures on some basic shapes (Larose and Franck, 1997).

Wind tunnels for aeronautical applications developed rapidly during the first half of the twentieth century, especially during and between the two world wars. The two basic wind tunnel layouts: the open circuit, or lsquo;N.P.L. (National Physical Laboratory) typersquo;, and the closed circuit, or lsquo;Gouml;ttingen-typersquo; were developed during this period, named after the research establishments in the U.K. and Germany where they originated. These two types are outlined in the following sections.

7.2.2 Open-circuit type

The simplest type of wind tunnel layout is the open-circuit or N.P.L. type. The main components are shown in Figure 7.2. The contraction, usually with a flow straightener, and fine mesh screens, has the function of smoothing out mean flow variations, and reduc-ing turbulence in the test section. For modelling atmospheric boundary layer flows, which are themselves very turbulent, as described in Chapter 3, it is not essential to include a contraction, although it is better to start with a reasonably uniform and smooth flow before commencing to simulate atmospheric profiles and turbulence.

The function of the diffuser, shown in Figure 7.2, is to conserve power by reducing the amount of kinetic energy that is lost with the discharging air. Again this is not an essential item, but omission will be at the cost of higher electricity charges.

Figure 7.2 shows an arrangement with an axial-flow fan downstream of the test section. This arrangement is conducive to better flow, but since the function of the fan is to produce a pressure rise to overcome the losses in the wind tunnel, there will be a pressure drop across the walls and floor of the test section that can be a problem if leaks exist. An alternative is a lsquo;blowingrsquo; arrangement in which the test section is downstream of the fan (see Figure 7.5). Usually a centrifugal blower is used, and a contraction with screens is

Figure 7.3 The Counihan method for short test sections.

The role of wind tunnels 141

essential to eliminate the swirl downstream of the fan. However, in this arrangement the test section is at or near atmospheric pressure.

Both the arrangements described above have been used successfully in wind engineer-ing applications.

7.2.3 Closed-circuit type

In the closed circuit, or Gouml;ttingen-type, wind tunnel, the air is continually recirculated, instead of being expelled. The advantages of this arrangement are as follows:

It is generally less noisy than the open-circuit type

It is usually more efficient. Although the longer circuit gives higher frictional losses, there is no discharge of kinetic energy at exit

More than one test section with different characteristics can be incorporated.

However, this type of wind tunnel has a higher capital cost, and the air heats up over a long period of operation before reaching a steady-state temperature. This can be a prob-lem when operating temperature-sensitive instruments, such as hot-wire or other types of thermal anemometers, which use a cooling effect of the moving air for their operation.

7.3 Simulation of the natural wind flow

In this section, methods of simulation of strong wind characteristics in a wind tunnel are reviewed. Primarily, the simulation of the atmospheric boundary layer in gale, or large-scale synoptic conditions, is discussed. This type of large-scale storm is dominant in the temperate climates, for latitudes greater than about 40 degrees, as discussed in Chapter 1.

Even in large scale synoptic windstorms, flows over sufficiently long homogeneous fetch lengths, so that the boundary-layer is fully developed, are relatively uncommon. They will occur over open sea with consistent wave heights, and following large fetches of flat open country or desert terrain. Bu


目 录

7.风洞的作用 1

7.1引言 1

7.2风洞布局 1

7.2.1历史 1

7.2.2开路的类型 2

7.2.3闭路的类型 2

7.3模拟自然风流 3

7.3.1相似性标准和自然增长方法 3

7.3.2短试验部分的方法 4

7.3.3模拟表面层 4

7.3.4热带气旋和雷暴风的模拟 5

7.4风效应结构模型 5

7.5局部压力的测量 6

7.5.1单点测量 7

7.5.2区域平均压力的测量。 9

7.5.3等效时间平均 10

7.6整体荷载和结构响应的建模。 10

7.6.1高层建筑的基准点模型试验。 10

7.6.2基础平衡技术。 13

7.6.3桥梁的断面和紧带模型。 14

7.6.4多模变形的造型 15

7.6.5烟囱的气动弹性模型。 16

7.6.6通过压力测量的结构荷载。 17

7.7堵塞效应和修正。 17

7.8计算风工程 18

7.9总结 18

参考文献 19

8 低层建筑 22

8.1介绍 22

8.2历史 22

8.2.1早期风洞研究。 22

8.2.2全面研究 25

8.3低层建筑风荷载的一般特征。 28

8.3.1压力系数 28

8.3.2压力系数的依赖关系。 29

8.3.3流量模式和平均压力分布。 30

8.3.4脉动压力 31

8.4有倾斜屋顶的建筑物。 35

8.4.1包层负载 35

8.4.2结构荷载和等效静力荷载分布。 37

8.5载荷及建筑 40

8.6内部压力 40

8.7总结 40

参考文献 41

9 高楼大厦 44

9.1介绍 44

9.2历史 44

9.3在高层建筑周围流动。 46

9.4.2矩形截面建筑的压力分布。 48

9.4.3波动局部压力和概率分布的性质。 49

9.4.4局部压力峰值的统计方法。 51

9.4.5玻璃在风荷载作用下的强度特性。 53

9.5整体加载和动态响应。 55

9.5.1一般响应特性 55

9.5.2建筑截面的影响。 56

9.5.3角落里修改 56

9.5.4跨风响应预测。 57

9.6沿和交叉风响应的组合。 57

9.7扭转载荷和响应。 59

9.8干扰影响 61

9.8.1逆风建筑 61

9.8.2顺风建筑 61

9.9阻尼 62

9.9.1结构阻尼 62

9.9.2粘弹性阻尼器 63

9.9.3调谐质量阻尼器 64

9.9.4调谐液体阻尼器 65



大多数实践中的结构工程师不会自己操作风洞,但他们可能是风洞组的客户,他们通常会通过模型测试为新建或现有结构提供风荷载信息。 出于这个原因,本章不会详细描述风洞技术。 有详细的参考资料,指导手册和实践手册(例如Cermak,1977; Reinhold,1982; Australasian Wind Engineering Society,2001; American Society of Civil Engineers,1999)。 然而,为了让受过教育的客户能够“向他们的风洞承包商提出正确的问题”,这里给出了足够的细节。




Kernot在澳大利亚墨尔本(1893年)首次使用风洞测量建筑物的风力。 图7.1给出了他称之为“吹气机”的装置的草图(Aynsley等,1977)。 现在这将被描述为“开路,开放测试部分”安排。 有了这些设备,Kernot就研究了各种钝体 - 立方体,金字塔,圆柱体等以及各种沥青屋顶上的风力。

图7.1 1893年W. C.克诺的“吹制机”草图(Aynsley et al., 1977)。


大约在同一时间,丹麦哥本哈根的Irminger(1894)利用烟囱烟道中的流动来研究一些基本形状的风压(Larose and Franck,1997)。

在二十世纪上半叶期间,特别是在两次世界大战期间和之间,用于航空应用的风洞发展迅速。 两种基本的风洞布局:开路,或“N.P.L. (国家物理实验室)类型“,并在此期间建立了闭路或”戈廷根型“,以英国和德国的研究机构命名。 以下部分概述了这两种类型







在封闭回路或Go-ttingen型风洞中,空气不断被再循环,而不是被排出。 这种安排的优点如下:


它通常更高效。 虽然较长的回路会产生较高的摩擦损失,但出口处不会释放动能。


然而,这种类型的风洞资本成本较高,并且在达到稳态温度之前,空气在长时间的运行中升温。 在使用温度敏感的仪器时,如热线或其他类型的热风速仪,这些仪器在运行时会使用移动空气的冷却效果,这可能是一个问题。









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