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ESCUELA TÉCNICA SUPERIOR DE INGENIEROS INDUSTRIALES Y DE TELECOMUNICACIÓN Titulación : INGENIERO INDUSTRIAL Título del proyecto: DEVELOPMENT OF A MEASUREMENT BOX TO MEASURE THE 3D WIND SPEED IN AN URBAN ENVIRONMENT Alumno: Alejandro Sola Alzueta Tutor: Pablo Sanchis Gúrpide Pamplona, 15 de Junio de 2010 ACKNOWLEDGEMENTS This thesis would not have been possible without the essential and generous support of many people. The personal and unconditional support and interest of my family throughout my studies and my entire life. The leadership and guidance of my promoters Dr. Abdellah Touhafi, Dr. Mark Runacres and Ing. Jochem Vermeir. The cooperation of Albert Van Steendam as my coordinator in Brussels and Dr. Pablo Sanchís as my promoter in Spain. The collaboration and help, when it was needed, of all my laboratory mates as well as the effort of Alain Wery helping me with the wind tunnel. I thank the Erasmushogeschool Brussel (EhB) for providing me of a laboratory to work in, as well as the Vrije Universiteit Brussel (VUB) for the availability of the wind tunnel to calibrate my sensors. I am very grateful to Rainwise company for making a fast effort to improve their products and their support to make this project better. This experience has been also possible thanks to my home university, Universidad Pública de Navarra, for providing me a platform to use my aptitudes and capacities to develop this project, for collaborating with the Erasmushogeschool Brussel in the Erasmus program and for a generous financial assistance. In addition to all the foregoing, I would really like to acknowledge all the international friends I have met this year for making me feeling like home and for their emotional support. 2 ABSTRACT The present work aims to build a low-cost three-dimensional anemometer to measure the wind speed and direction in an urban environment. To begin with, some research on basic principles in scientific literature and also in patent database was done. Secondly, a market study was carried out and two propeller anemometers were purchased. A hi-tech ultrasonic sensor was also purchased to gather accurate measurements and to serve as input for the calibration of the low-cost anemometer. The propeller anemometers were then calibrated in a wind tunnel and some unexpected measuring errors became visible. Their accuracy was not as high as it had been anticipated in the datasheets. This resulted in a collaboration with the manufacturers to test and improve their products. Some more tests were carried out and concluded with great results. Then, the three-dimensional sensor was assembled using the two propeller anemometers and it was subsequently cross-checked with an ultrasonic anemometer in a roof of the Erasmushogeschool Brussel. Finally, a program was created to collect the data from the ultrasonic sensor and store the information in a file. To sum up, this project meets all the desired goals: it works autonomously, collects the data, and is movable. In addition, some other technical statements were concluded: at low wind speeds, the propeller anemometers also had a low resolution and measurements corresponding to the horizontal plane were more accurate than those for the vertical component of the wind. One of the most significant results of this project is the fact that this work allowed helping the manufacturers to improve the propeller anemometers; their accuracy was reduced by more than 5%. In addition, the development of a program to log the wind speed data from the ultrasonic anemometer eliminated the need for an expensive data logger. 3 INDEX CHAPTER 1. INTRODUCTION GENERAL INTRODUCTION DESCRIPTION OF THE THESIS... 7 CHAPTER 2. THE BASICS THE IMPORTANCE OF A 3D ANEMOMETER TYPES OF ANEMOMETERS ROTATING VANE ANEMOMETER CUP ANEMOMETER PROPELLER ANEMOMETER HOT WIRE ANEMOMETER ULTRASONIC ANEMOMETER LASER ANEMOMETER CHAPTER 3. MARKET STUDY D ANEMOMETER ROTATING VANE ANEMOMETER HOT WIRE ANEMOMETER D ANEMOMETER CUP ANEMOMETER PROPELLER ANEMOMETER ULTRASONIC ANEMOMETER D ANEMOMETER LASER ANEMOMETER CHAPTER 4. ULTRASONIC ANEMOMETER PURCHASE CHAPTER 5. LOW COST ANEMOMETER PURCHASE CHAPTER 6. CALIBRATION ULTRASONIC ANEMOMETER CALIBRATION WINDLOG CALIBRATION CHAPTER 7. ASSEMBLY CHAPTER 8. MEASUREMENTS D VECTOR CONSTRUCTION WIND COMPONENTS WIND MEASUREMENT CHAPTER 9. COMPARISON CHAPTER 10. DATA RETRIEVING LOW-COST ANEMOMETER ULTRASONIC ANEMOMETER CHAPTER 11. CONCLUSIONS AND RECOMMENDATIONS CHAPTER 12. BIBLIOGRAPHY CHAPTER 13. APPENDIX Chapter 1. INTRODUCTION 6 1 GENERAL INTRODUCTION The 3D anemometer development is part of research carried out in the Erasmushogeschool Brussels (EhB) by different research groups. On the one hand, there is the mechanics group which is interested in the use of wind turbines in an urban environment. The vertical component of the wind is required due to the possible occurrence of an upstream in built-up environments. This group is headed by Dr.Mark Runacres. On the other hand, there is the Electronics and ICT group which has an interest in a 3D anemometer to complete its sound studies, to account for the influence of wind speed on acoustics. This group is headed by Dr. Abdellah Touhafi. The purpose of this thesis is to assemble a simple and inexpensive threedimensional anemometer sensor in order to measure the wind speed and direction in an urban environment. By mounting two integrated propeller anemometers, calibrated and checked, 3D measurements can be carried out and data can be collected. This thesis also involves the purchase of a hi-tech ultrasonic anemometer to perform precise measurements that serve as input for the calibration of the low-cost anemometer. This project produced the following results: - The sensor fulfils the desired requirements: it works autonomously, collects the data and is movable. - The accuracy of the propeller anemometers purchased was reduced by more than 5%. - Measurements corresponding to the horizontal plane are more accurate than those for the vertical component of the wind. - At low wind speeds, the propeller anemometer also has a low resolution. - The development of a program to log the wind speed data from the ultrasonic anemometer eliminates the need for an expensive data logger. 7 1.1 DESCRIPTION OF THE THESIS CHAPTER 1 This chapter presents the General Introduction and describes the aims and the context in which this project is developed. CHAPTER 2 This chapter points out the importance of an anemometer and describes the fundamentals of all kinds of wind sensors. CHAPTER 3 This chapter consists of a market study covering the diverse wind sensors and emphasizing their main features. CHAPTER 4 This chapter includes the ultrasonic anemometer purchase after comparing the main features between several ultrasonic models. CHAPTER 5 This chapter involves the comparison of some low-cost sensors features and the later purchase decision. CHAPTER 6 This chapter describes the process of calibration carried out to know the exact measuring error the purchased anemometers have. CHAPTER 7 This chapter shows the way the three dimensional low cost anemometer is assembled. 8 CHAPTER 8 This chapter describes the process of how the different components of the wind speed are measured by the low-cost anemometer. CHAPTER 9 This chapter compares the low cost anemometer and the reference, the ultrasonic anemometer. CHAPTER 10 This chapter consists of the explanation of the different ways data can be collected from the purchased anemometers. CHAPTER 11 This chapter contains the final conclusions and the corresponding recommendations. CHAPTER 12 This chapter includes the bibliography used to write this thesis. CHAPTER 13 This appendix consists of the datasheet of the propeller anemometer and the manual of the ultrasonic sensor purchased for this project. 9 Chapter 2. THE BASICS 10 1 THE IMPORTANCE OF A 3D ANEMOMETER An anemometer is an apparatus for measuring the force of air or the speed of wind and usually its direction. This term is derived from anemos, which means wind in Greek. Depending on the mechanisms, there is a diversity of anemometer types, explained in the next section. [10] The development of an anemometer is critical to the installation of a wind turbine. A wind turbine needs to be oriented to the wind direction. The power generated is proportional to wind speed which passes across the turbine, but cubed, so a wrong position would mean losing a lot of power and, in an economical point of view, losing money. [1] Thus, the wind turbine installed in the EhB campus will have to be oriented to the predominant wind direction and the installation of an anemometer is highly recommended before considering any installation of this type. A typical big wind turbine located in a landscape and made by a common manufacturer such as Gamesa has two 2D anemometers, wind vane and ultrasonic anemometer, while the purpose of this project is a 3D anemometer. [2] This may be a waste of money because a big wind turbine would produce much more power and consequently much more money than a wind turbine installed in the EhB campus. However, there is one main reason to why 3 dimensions are required here. That reason is the urban environment. Unlike the almost laminar airflow in landscape, on-site wind farms, the wind regime in urban environment is highly affected. These areas act as a brake to wind, creating a highly dynamic and turbulent flow which includes a strong vertical component. This vertical speed is often disregarded when assessing the wind energy potential. [1][30] Nowadays, there is a lack of understanding about wind flows in this environment: they are subject to frequent changes in wind speed and direction. In addition, wind turbulence is high because of the obstacles of the urban environment. This project attempts to create a wind sensor so that this effect can be studied. 11 Figure 1: Simulation of wind over a building [33] 12 2 TYPES OF ANEMOMETERS 2.1 Rotating Vane Anemometer Rotating vane anemometers are simple devices which provide fast, reliable and accurate readings of air velocity, but not wind direction measurements. They are handheld and digital, usually with a small fan, a LCD display and a data-logger attached. This tool is very useful when a quick measurement is needed, for example, grilles, ducts, or diffusers [3] As it does not provide the direction from which the wind blows, rotating vane anemometers should be placed facing the desired direction. It should be held in the hand and the person looking at the display directly. Figure 2: Kestrel 4000 Pocket Weather Tracker [25] When the wind blows, the fan blades and a small generator connected to them start spinning. The faster the rotor blades turn, the quicker the generator spins and the higher the electric current it will produce. Precisely calibrated, this device will provide a mathematical relationship between the electric current and the wind speed. [11] However, this generator is directly connected to an electronic circuit, so there is no need to measure the current because the data appears automatically in the digital display. 13 Advantages: The core advantage of this device is its size and mobility. It is quite small and handheld. It can be kept on hand in various places and situations and provide reliable air velocity measurements in harsh environments. Moreover, its low price, convenient size, and considerable accuracy are particularly attractive features. The rotating vane anemometers can measure wind speed in all directions needed just pointing it into the wind flow. Disadvantages: On the other hand, it is not typically considered for wind measurement research with the exception of some practical situations where accuracy is not a priority. Furthermore, the range of wind from where this tool can gather information is significantly reduced (0-30m/s) compared to other types of anemometer. The rotating vane anemometer is a mechanical tool, so the moving parts can sometimes become defective. [3] 14 2.2 Cup Anemometer This is the most common and oldest style anemometer, invented in 1846 by Dr. Thomas Romney Robinson of Armagh University. The rotating cup anemometer consists of three or four semi-spherical or conical cups attached to arms of a hub that is allowed to revolve freely around a normally vertical shaft. [12] As the current of air blows against the cups, the anemometer starts rotating. This movement is due to the wind forces pushing the cups and creating some moments around the vertical shaft, the center of rotation. The frequency of rotation can be translated as wind speed. This is possible because, as it will be demonstrated next, the anemometer rotates at a speed which is proportional to the wind speed. An example with a three cup anemometer is showed next: Figure 3: Velocities and torques in a three cup anemometer [28] 15 v: wind speed : air density C dv, C dx: drag coefficients for the concave and convex faces (typical values: 1,4 and 0,4 respectively) A: frontal area R: rotor radius : rotating speed M R: resistant torque = = Supposing null the resistant torque and steady state, when the rotating speed is constant there is a torque balance ( =0), and the expression can be simplified to: = =0 Thus, a second grade equation is obtained: =0 The solution is: = ± ; = [28] What was desired has been demonstrated; the linear sensitivity of the cup anemometer to wind speed. Moreover, it shows how this constant, k, does not depend on the size of the anemometer, only on the drag coefficients of the cups. Another way to see the same aspect is: = = 16 This means that the wind speed is proportional to the tangential velocity (v T) of a point situated in the center of a cup. This new constant, k, is usually a value between 2 and 3, depending again on the drag coefficients. These constants and so the relationship between the wind speed and the rotation frequency is determined by calibration. [7] However, the rotating speed cannot directly be known unless a display is available to show it. To that end, some anemometers offer different solutions depending on the output signal. This is valid for all types of anemometers, but the only difference is the nature of the signal: analog or digital. Rotation speed can be measured by a number of different mechanisms, but tiny magnets are often used. They are mounted on the cups and each time the anemometer completes a full rotation the magnet is detected by what is called a reed switch. Then, when the magnet is nearby, the reed switch closes and triggers an output electric pulse, before opening again when the magnet goes away. Frequency is then converted into wind speed as it will be shown in the market study. [4] If the anemometer has a frequency-to- voltage/current converter, the main outputs will be voltage or current signals, which are also proportional to wind speed. Finally, the shaft can also contain an encoder in order to obtain a digital output. Figure 4: Cup anemometer [26] 17 Advantages: The cup anemometer is an easy-to-use device and it is commonly used nowadays. The reason why the cup anemometer is and has been so successful is the simple construction, the low price, and other distinctive characteristics. Disadvantages: This anemometer is a mechanical tool so its moving parts will wear out. It also has an effect called overspeeding. This means that in fluctuating winds, the mean indication will be higher than the true average wind speed. Moreover, it reacts slowly to sudden changes in wind. [29] 18 2.3 Propeller Anemometer Propeller anemometers are also called wind vane anemometers, windmill anemometers or simply helicoid propeller anemometers. They normally consist of a propeller, with three or four blades, which rotate on a horizontal shaft. This axis must be parallel to air flow, so when the wind varies in direction the wind sensor is turned into the wind flow. Following these changes is the purpose of the vane. It is used in conjunction with the propeller and they are both in the main body, one in each side of the anemometer. Figure 5: R M Wind Monitor Model [5] The propeller works in a similar way to how the rotating vane anemometer does. The blades are connected to a small generator and when the air flow blows, they rotate. The propeller rotation produces an AC sine wave voltage signal with frequency directly proportional to wind speed. Measuring its frequency, the velocity of the wind will be known. [6] There is one change: how the vane works and how the signal is processed into a specific wind direction. This wind direction sensor has a precise potentiometer which is excited by a determined voltage signal. Depending on the position of the vane the output voltage will change, hereby measuring this output voltage, the vane angle will be known and consequently so will the wind direction. 19 Advantages: Propeller anemometers are simple and compact. They do not have a big size, which makes them hand-held and easy-to-use. Their response to gusts is better than cup anemometers and it is clear that are reasonable sensors for measuring turbulence. In addition, their wind range is the largest, far away from other sensors ranges. Disadvantages: This tool is also mechanical so it has moving parts which can wear out. Another disadvantage is the necessity of being turned into the flow direction. However, the most outstanding one is the inability in turbulent wind to track sudden wind changes. Hence, this effect can place the propeller off the wind direction resulting in a lower wind speed measurement. [29] 20 2.4 Hot Wire Anemometer Hot wire anemometers have been extensively used for a long time as a research tool in fluid mechanics. One of the main advantages of these devices is their highfrequency response. They are capable of reading instantaneous values of velocity up to very high frequencies. Thus, it is extremely useful in measuring the turbulent fluctuations of the fluid flow. Hot wire anemometers operate on the principle of heat transfer. They normally measure fluid velocity taking into account the amount of heat extracted by the air flow from the heated wire. This fine filament is often heated to a constant and fixed temperature (CTA, Constant Temperature Anemometer), though some devices heated by a constant current (CCA) or by a constant voltage (CCV) are also available. [7][13] The current then passes through an electrical resistance and the energy is converted to heat. As the fluid flows over the wire, it is cooled and an amount of heat is lost due to convection. In order to maintain the filament at a constant temperature, the current increases. As this current is a function of the fluid velocity which passes over the wire, measuring its change, the velocity of the fluid will be easily known. In case the anemometer is a constant current device, the heat loss can be obtained by measuring the change in wire temperature. As the electrical resistance of most metals is dependent upon the temperature of the metal, the value of the resistance will help to know definitely the flow velocity. [13] Figure 6: Hot wire anemometer [15] 21 This type of anemometer mainly consists of small diameter probes that allow doing measurements in tight spaces and hard to reach areas. These sensors have such an electrical resistance that it can be easily heated with low current and voltage levels. The wires are mainly made of tungsten, platinum and platinum-iridium alloy. Advantages: This anemometer stands out because of its capability to make measurements in tough environments such as pipes or tubes flows. In addition, it has a good spatial resolution because it can measure the flow in a precise location. For these reasons, this tool is perfect for ducts. It also reacts quickly to sudden changes in air flows. Disadvantages: Like rotating vane anemometers, hot-wire sensors have the lowest measuring range on the market. Moreover, the accuracy of the measurements is quite poor (±
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