适用于厄立特里亚电站小型风力机研究

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摘要

厄立特里亚，非洲东北部的一个国家，一直积极从事不同的可再生能源，特别是风

能的开发和利用，在进行独立初步调查的头几年，我们研究全国各地不同地区的风速。

厄立特里亚记录分析表明了在厄立特里亚首都阿斯马拉附近的中央高地的边缘风力资

源情况。测试在两个地点进行，在南部港口城市 ASEB 分析得到的风速记录显示在 10

米高度的年平均风速为 9.5 米/秒。沿红海 200 公里的海岸线表面风速记录表明，厄立特

里亚可能会发现类似的潜力。基于这些发现，在这个区域风力发电应该比进口柴油产电

更廉价。在厄立特里亚的风况决定是否需要一个小规模的风力涡轮机产生平均风速在 8

米/秒的功率。

在这篇论文的主要工作包括：

（1）该论文的第一部分讨论了在厄立特里亚风力发电和风力资源情况。该国已分为

3个区域：东部低地，中部高原地区和西部低地。每个地区都有变电站的风速测量，以

图形和表格总结。正如在图中表示的，厄立特里亚风资源的大部分地区是适用于发电的；

（2）我们已对风力涡轮机技术和它的空气动力学已进行了深入讨论。水平轴风力涡

轮机叶片气动外形的设计是基于动量理论与叶素理论，该方法被用于优化叶片的和弦和

扭曲分布。转子采用 NREL S809 翼型轮廓的内侧，跨中和外侧站的叶片。设计叶片的

几何形状和结构的表中给出，其弦，厚度和扭曲分布示于图中。 S809 翼型的升力和阻

力系数确定从叶片流场中求解。在一定攻角时，升力系数有所增加，然而在 16 度角的

攻角时发生失速，而且是一个巨大阻力增加和升力的急剧下降。在强度设计分析方面，

本论文进一步研究在给定的翼型下拖尾和粗糙度的影响，结果表明，较尖锐，粗糙的表

面，钝型，光滑的表面上提供更高的升力系数；

（3）本文运用一个三维的修正模型来计算二维翼型系数，在叶片的内部部分

r/R=30％和 r/R=60％上观察到翼型件的特性的变化。在 r/R=80％和 r/R=95％的翼型的

特性是接近到 2D。这主要是因为尖端效应。如果轴向诱导因子在叶片处大，然后，流

入角一定会小，这将导致减少升力。这被称为叶尖损失，因为只发生在叶片的最外部分

的效果。

关键词：风力机厄立特里亚风能资源电力需求

Abstract

Eritrea, a country in the north east of Africa, has been actively engaged in the

development and utilization of different renewable energy sources, especially of wind, since

the first few years of independence a preliminary survey was conducted to study wind

velocities in different parts of the country. An analysis of national Eritrean and historical

Italian wind records indicated marginal wind resources in the central highlands near the

Eritrean capital of Asmara. An analysis of wind speed records obtained at two sites in the

southern port city of Aseb indicate mean annual wind speed of 9.5 m/s at 10-m height at the

windier site. Surface wind speed records for the Red Sea suggest that similar potential may be

found along the lower 200 km of the Eritrean coastline. Based on these findings,

wind-generated electricity in this region should be substantially cheaper than the current

supply generated from imported diesel. The wind conditions in Eritrea determine the need for

a small-scale wind turbine to produce usable power at an average wind speed of 8 m/s.

Main work in this thesis includes:

(1) The first part of the thesis discusses the wind power and wind resources in Eritrea.

The country has been divided in to three regions as eastern lowland, central highlands and

western lowlands. Each region has substations in which their wind speeds are summarized in

graphs and tables. As it is indicated in the graph most parts of Eritrea wind resources are

suitable for generating electricity.

(2) Secondly, wind turbine technology and its aerodynamics have been discussed in

depth. The blade aerodynamic outline of horizontal axis wind turbine is designed based on

blade element theory associated with momentum theory. The method is used to optimize the

chord and twist distribution of the blade. The rotor employs NREL S809 airfoil profile at

inboard, mid span and outboard stations of the blade. The geometry and configuration of the

designed blade are given in tables and its chord, thickness and twist distributions are shown

in figures. The lift and drag coefficients for S809 aerofoil are determined from Xfoil flow

solver. There is an increase in lift coefficient for a certain angle of attack however, at 16

degrees angle of attack a stall occurs, and there is a massive increase in drag and sharp

reduction in lift. To strength the design analysis a further study was taken on the trailing and

roughness effects of the given airfoil and results show that a blunt and clean surface provided

high lift coefficient as compared to the sharp and rough surface respectively.

(3) Furthermore, a 3D correction model was given to the 2D airfoil coefficient results, in

which large changes of the airfoil characteristics are observed on the inner part of the blade,

r/R=30% and r/R=60%. At r/R=80% and r/R=95% the airfoil characteristics are close to 2D.

This is mainly because of tip effects. If the axial induction factor

is large at the blade

position then, the inflow angle will definitely be small and this causes the reduction in the lift

force. This is known as tip loss because the effect occurs only at the outermost parts of the

blade.

Key Words: Wind turbine, Eritrea, Wind resources, Power needs

Table of Contents

摘要

Abstract

Table of Contents ............................................................................................................................ 1

Chapter 1 Introduction .................................................................................................................... 1

1.1 Development of wind turbine ............................................................................................ 1

1.2 Wind turbine technology .................................................................................................... 2

1.3 Wind Turbine Class and Certification ................................................................................ 3

1.4 Objectives .......................................................................................................................... 4

Chapter 2 Wind resources and power needs in Eritrea ................................................................... 6

2.1 Natural wind resources in Eritrea ...................................................................................... 6

2.1.1 Eastern and South Eastern Stations .......................................................................... 8

2.1.2 Central Highland Stations ...................................................................................... 10

2.1.3 Western Lowland Stations ...................................................................................... 12

2.2 Wind power potential ....................................................................................................... 13

2.3 Power consumption .......................................................................................................... 13

2.4 Selection of wind turbines technology for Eritrea ........................................................... 15

Chapter 3 Aerodynamics of wind turbines .................................................................................... 18

3.1 Principle of airfoil lift ...................................................................................................... 18

3.2 Actuator disc model ......................................................................................................... 21

3.3 Blade element theory ....................................................................................................... 23

3.4 Tip speed loss ................................................................................................................... 25

3.5 Blade airfoils for small.scale HAWT ............................................................................... 26

3.5.1 Viscous effects on airfoil aerodynamics ................................................................ 28

3.6 Stall and control ............................................................................................................... 31

Chapter 4 Performance prediction of airfoils and blades .............................................................. 33

4.1 2D airfoil performances ................................................................................................... 33

4.1.1 Effects of Incidence Angle ..................................................................................... 33

4.1.2 Trailing edge effects ............................................................................................... 35

4.1.3 Roughness effect .................................................................................................... 36

4.1.3 3D correction models ............................................................................................. 37

4.2 Rotor Blade geometry ...................................................................................................... 38

4.2.1 Chord distribution .................................................................................................. 39

4.2.2 Thickness distribution ............................................................................................ 40

Small Scale Wind Turbines Aimed at Power Generation in Eritrea

4.2.3 Twist distribution ................................................................................................... 40

4.2.4 Coefficient of performance .................................................................................... 41

Chapter 5 Conclusion .................................................................................................................... 43

Nomenclature ................................................................................................................................ 44

Appendix: Summarized Eritrean wind energy data ............................................................... 45

References ..................................................................................................................................... 51

Acknowledgements ....................................................................................................................... 53

Chapter 1 Introduction

1.1 Development of wind turbine

Since antiquity, mankind has been using wind energy; it is thus not a new idea. For

centuries, windmills and watermills were the only source of motive power for a number of

mechanical applications, some of which are even still used today. But one of today’s greatest

global challenges is the need for more affordable, reliable, clean, secure and renewable

sources of electricity. Relying solely on coal, oil, natural gas and nuclear fuels to generate

electricity is far from being optimal. Fossil fuels are neither renewable nor clean. Their

extraction, transportation and combustion generate air emissions, acid rain, water pollution,

and, most importantly, CO2 emissions that are causing climate change. Moreover, the

constantly increase of fossil fuel price has shown a negative impact on current world

economy. On the other hand nuclear energy has a major drawback in managing the nuclear

waste disposal.

The sudden increase in the price of oil stimulated a number of substantial Government

funded programs of research, development and demonstration. In the USA this led to the

construction of a series of prototype turbines stating with the 38 m diameter 100 kW Mid-0 in

1975 and culminating in the 97.5 m diameter 2.5 MW Mod-5B in 1987. Similar program

were pursued in the UK, Germany and Sweden. There was considerable uncertainty as to

which architecture might prove most cost effective and several innovative concepts were

investigated at full scale. In Canada, a 4 MW vertical axis Darrieus wind turbine was

constructed and this concept was also investigated in the 34 m diameter Sandia Vertical Axis

Test Facility in the USA. In the UK, an alternative veridical axis design using straight blades

to give an H type rotor was proposed by Dr. Peter Musgrove and a 500 KW prototype

constructed. In 1981 an innovative horizontal axis 3 MW wind turbine was built and tested in

the USA. This used hydraulic transmission and, as an alternative to a yaw drive, the entire

structure was orientated into the wind. The best choice for the number of blades remained

unclear for some while and large turbines were constructed with one, two or three blades [10].

The stimulus for the development of wind energy in 1973 was the price of oil and

concern over limited fossil fuel resources. Now, of course, the main driver for use of wind

turbine to generate electrical power is the very low CO2 emissions and the potential of wind

energy to help limit climate change. Wind energy was identified as having a key role to play

in the supply of renewable energy with an increase in installed wind turbine capacity from 2.5

GW in 1995 to 40 GW by 2010. Since 2001 there was some 12 GW of installed wind turbine

capacity in Europe, 2.5 GW of which was constructed in 2000 compared with only 300 MW

in 1993. The average annual growth rate of the installation of wind turbine in Europe from

1993.9 was approximately 40%. The distribution of wind turbine capacity is interesting with

in 2000, Germany accounting for some 45% of the European total, and Denmark and Spain

each having approximately 18%. There is some 2.5 GW of capacity installed in the USA of

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摘要：

摘要厄立特里亚，非洲东北部的一个国家，一直积极从事不同的可再生能源，特别是风能的开发和利用，在进行独立初步调查的头几年，我们研究全国各地不同地区的风速。厄立特里亚记录分析表明了在厄立特里亚首都阿斯马拉附近的中央高地的边缘风力资源情况。测试在两个地点进行，在南部港口城市ASEB分析得到的风速记录显示在10米高度的年平均风速为9.5米/秒。沿红海200公里的海岸线表面风速记录表明，厄立特里亚可能会发现类似的潜力。基于这些发现，在这个区域风力发电应该比进口柴油产电更廉价。在厄立特里亚的风况决定是否需要一个小规模的风力涡轮机产生平均风速在8米/秒的功率。在这篇论文的主要工作包括：（1）该论文的第一部分...

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