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effect of modern civilization 代写

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  • CHAPTER I
     
    INTRODUCTION
     
    1.1            BACKGROUND
    The effect of modern civilization on our dwindling climate change has spur series of un-relented research in developing alternative energy sources that will help minimize the depletion of the ozone layer and save our planets from the adverse effects of high dependence on the black gold-Crude oil. According to reports from British Petroleum and Royal Dutch shell, one third of the world energy has to come from renewable sources by 2050 ( alternate.org) . This is in line with the prediction from the quarterly magazine published by European Commission of the feasibility of 80% of the global energy coming from renewable sources by the mid century. (RTD, 2007). The prediction is a foreseeable future of less dependence on crude oil as the resource is rapidly depleting. There are various alternative energy sources ranging from Biomass, solar, Geothermal, hydro and wind. The method of cultivation of these energy sources to replace the quickly diminishing oil is the subject of current research among the various fields of renewable energy.
    Wind is generated as a result of the movement of air. The sun is actually the center of this movement: as the sun heats the land, the air above heats up and acquire more kinetic energy and therefore rises up. This warm air is been replace by colder air from below. Due to the different conductivity of land and sea, the air in the lands heats up faster than the air in the sea. This is why the seashore is windier as cold air from the sea always rises or blows towards the land to replace the warm air. The wind turbine harnessed this kinetic energy of the wind and turns it into a mechanical energy. The figure below illustrates the wind energy process. The amount of energy available to be tap in essence depends on the wind power. The wind power is a measure of the wind speed which is a measure of how much wind is available
     
     
    Figure 1: How wind turbine works
     
     According to the center for sustainable systems at the University of Michigan, Horizontal Axis Wind Turbine is the predominant operational wind turbine. Most of the electricity produced from wind energy today is produced by HAWT. Although Vertical Axis wind turbines have some advantages over HAWT by means of easy operations, however they cannot produce power efficiency as HAWT.
    The rotor is the main part of the wind turbine and consists of two or three blades that are connected to the hub. The rotor and hub are connected to the nacelle. The Nacelle is a covering for internal parts such as: generator, drive train and control unit. The drive train is the rotating part of the wind turbine excluding the rotor and consists of gearbox, shafts and mechanical brakes. Control unit and generator are connected to the Nacelle. There are various ways to control the power production of wind turbines which are aerodynamic control also known as stall control or by variable pitch blades (pitch control) which operates with fixed or variable rotor speed. Balance of electrical systems contains cables, switch gear and transformers for electricity generation. Figure2 below highlights the different parts of a wind turbine.
     
    http://www.turbinesinfo.com/wp-content/uploads/2011/07/Parts-of-Windt-Turbines.jpg
    Figure 2: Different parts of a wind turbine. (Courtesy of turbines info.com)
     
     
    1.2            PROBLEM STATEMENT
    The design of wind turbine is a complex process. And when the performance of the wind turbine is considered, the design of the turbine blade is paramount.  The design engineer is poised with the problem of determining the best shape of the blade for optimal performance, the pitch angle and the twist angle. In order to establish an optimum system that produces as much power as possible with low cost and low noise levels, the ideal case is the optimization of this design process with all of the components included. However, this is not possible all the time. This idealized procedure needs too much time and effort to produce best wind turbine geometry by using the most accurate methods for all phases. As a result, in most of the design applications, accurate design methods are used partially. Optimization of the aerodynamic of the wind turbine is the first place to start.
    1.3            OBJECTIVE OF PROJECT
     
    This project seeks to understand the difficulties face in using computational Fluid dynamics analysis to predict the flow around the blades of the horizontal axis wind turbine. Of much interest is the aerodynamic of the blade and the entire rotor.
     
    The main Objectives of this study are:
    1.      CFD Analysis of a wind Turbine blade.
    2.      Aerodynamics analysis of the  horizontal axis wind turbine rotor
    The experimental values needed for the CFD comparison study will be obtained from previous studies and from analytical calculations. In fulfilling the above objectives, the following sub-objectives will also be achieved:
    1.      2 dimension and 3Dimensional computer cad modeling of a wind turbine rotor according to the twist data and chord of NACA 4415 airfoil.
    2.      Analysis of the modeled wind blade and rotor using any of the ansys package (ansys CFX/ FLUENT) and SolidWorks flow Simulation (formally cosmos Flow).
    3.      Calculation of Power and pressure distribution at various speeds.
    The final stage of the project will be CFD simulation of a full Horizontal axis wind turbine comprising of the entire rotor-hub assembly, tower and the ground. This will give an interesting insight on wind flow behavior over the rotor in the presence of the tower.
     
    1.4              SCOPES
     The scopes of this project are:
    i.                    Aerodynamics study of a wind turbine blade
    ii.                  2D & 3D modeling of a wind turbine blade
    iii.                Modeling of an horizontal axis wind turbine
    iv.                CFD simulation of wind turbine blade.
     
    1.5              REPORT ORGANIZATION
    This section provides overview of the content and layout of this project report.
    Chapter I      introduce the concepts of the project starting with project background, problem statement, objectives and scope of the project.
    Chapter II focus on the theoretical part of the project, an explanation of some of the theories surrounding this project and review of the work that has been done by others as relate to the topic of this project. These works are also summarized into distinct grouping.
    Chapter III   discus the methodologies use in this project, concepts and theories on horizontal axis wind turbine, CFD simulation and Finite volume methods are explain. The work done in this project ranging from the aerodynamics of the turbine blade to the modeling and simulation of the HAWT is explained.
    Chapter IV   is about the results obtained, discussion, analysis and interpretation of this result.
    Chapter V    Conclusion is drawn on the results obtained and the entire project experience. Recommendations are made for future works.
     
     
     
     
     
     
     
     
     
     
     
    CHAPTER II
     
    LITERATURE REVIEW
     
    2.1              INTRODUCTION
    In this section, some relevant literatures are reviewed. Reviewing these literatures gives the insight into the reporting’s and documentations of what has been published by others and the tremendous pace with which innovations has been carried out on wind energy generation and distribution is something to be awe of. But with these innovations come several methodologies and concepts that have not been fully developed and the many challenges that are faced by researchers in bringing their hypothesis into fruition.
     
    2.1.1     Basics of wind turbine
    The focus on this review is the horizontal axis wind turbine, they are predominant and they are the subject of discussion. Approximately 2% of the solar energy striking the Earth’s surface is converted to kinetic energy in wind. The distribution of wind energy is heterogeneous; both across the surface of the Earth and vertically through the atmosphere.2 Wind turbines convert the wind’s kinetic energy to electricity without emissions. Wind power is proportional to the cube of wind speed. Because wind speeds are lower close to the earth’s surface a phenomenon called “wind shear” more wind power is available higher off the surface. The hubs of most modern wind turbines are 70-100 meters off the ground. Potentially, global onshore and offshore wind power at commercial turbine hub heights could provide 840,000 TWh of electricity each year, while total global electricity consumption from all sources in 2008 was about 17,400 TWh. Similarly, the U.S. annual potential of 68,000 TWh (lower 48 states) well exceeds annual U.S. electricity consumption of about 3,700 TWh (and growing).
    The capacity factor of a wind turbine is its average power output divided by its maximum power capability. Capacity factor depends on the quality of the wind at the turbine. Higher capacity factors imply more energy generation. Most HAWT extract 40% or more of the energy from the wind that passes through the rotor area. The theoretical maximum efficiency of a HAWT is under 50%. On land, capacity factors in the range of 0.25 to 0.40 are considered reasonable. Offshore winds are generally stronger than on land, and capacity factors can exceed 0.50, but offshore wind farms are more expensive to develop and maintain. Most offshore turbines are currently placed in depths of 30m or less.
     
     
    2.1.2      Overall Trend in What has been published
    There is an increase level of study in the field of renewable energy. Research on wind energy has tripled over the past decade and there continue to be more interest in the subject. From the study of the design of simple wind turbine for  local consumption to the building of complex high earn wind machines for public electric generation, the theory and concepts involve has generated much interest and much anticipation in finding out design methods and better formalization so as to design optimal system. Since the design of turbine rotor is a complex problem of many characteristics, many of the literatures publish has been on raveling a new optimal model of aerofoil for better and optimal capturing of wind energy. Many of these models has been analyze base on the Blade element Momentum (BEM) theory. There continue to be influx on the aerodynamic performance of the rotor and advanced FEM tools has been utilized in many of the literatures to study this.
    Also there is beginning to be concern on developing wind turbine systems for urban applications, which many of the literatures has come up with innovative design of wind energy machines to replace the roof of high rise buildings. These are tremendous achievement and with more countries investing in clean and renewable energies there is going to be more designs of this like and better in the coming years.
     
     
    2.1.3        Common Denominator in what has been Published
    For better understanding and for the purpose of this literature reviewed, the literatures reviewed are grouped into two main headings:
    Ø  Aerodynamic Analysis of wind turbines
    Ø  Modeling, simulation and performance analysis of wind turbines.
     
     

    2.1.4 Aerodynamic Analysis of Wind Turbine

    There continue to be a high interest on the aerodynamic design and performance analysis of the wind turbine. Special interest has been on the blade and rotor design. Many of the literatures use the blade element theory in their design. This is not surprising as the structure and aerodynamic performance of the blade plays a vital role in the overall performance of the wind turbine.
    As pointed clearly by Arvind et al (2011), The HAWT rotor design is a complex problem and as such can be formulated as a constrained of multi-objective optimization problem with respect to: geometric and operational characteristics, as maximization of output generated, minimization of generated vibration, minimization of blade material cost, minimization of stress and deflection in rotor fulfillment of appropriate strength requirement, by the blade structure. The following papers reviewed are related to aerodynamic performance of the wind turbine.
     
    Ø  Arvind Singh Rathore, Siraj Ahmed, (2011). Design and Analysis of Horizontal axis wind turbine rotor.
    Ø  Emrah Kulunk, Nadir Yilmaz: Computer Aided Design and Performance Analysis of HAWT Blades.
    Ø  Ernesto Benini, Andres Toffolo: Optimal Design of Horizontal-Axis Wind Turbines Using Blade-Element Theory and Evolutionary Computation
    Ø  Juan M´endez, David Greiner:Wind blade chord and twist angle optimization by using genetic algorithms
    Ø  M.C Robinson, M.M Hand, D.A. Siuns, J. Shreck: Horizontal axis Wind Turbine Aerodynamics: Three dimensional, Unsteady, and Separated Flow Influences.
     
     

    2.1.5 Modeling simulation and performance Analysis

    Some of the literatures tends to discuss and assessed the performance of wind turbines under different operation conditions, the economics involve, reliability and general performance of these systems. Many of the authors discuss this through numerical analysis; others combine it with experimental assessment. Some of the literatures under this denominator are:
    Ø  S. Carcangiu et al. Computational Fluid Dynamic Simulation of an Innovative system of wind power generation.
    Ø  Hiyoyuki Hirahara et al: Testing basic performance of a very small wind turbine designed for multipurpose.
    Ø  Jan Weinzettel, Marte Reenaas, Christian Solli and Edgar G. Hertwich, Life cycle assessment of a floating offshore wind turbine
    Ø  Djohra Saheb-koussa, M. Haddai, M. Belhanel, Modeling and Simulation of wind generator with fixed speed wind turbine under Matlab-Simulink.
     
     
     

    2.2 Summary of individual Literatures

    The following literatures are some of the papers reviewed in the process of this literature review. A great deal of time has been taking to summarized them as other wind energy books and resources has been consulted in order to gain an adapt understanding of the works published in these literatures.
     
     
    Optimal Design of Horizontal-Axis Wind Turbines Using Blade-Element Theory and Evolutionary Computation
    Ernesto et al. (2002) conducted a multi-objective optimization problem. In this research, a wind blade was modeled using a fixed airfoil family at four different stations along the span. The design variables were the rated power of the turbine, the radius as well as chord length and pitch angle distributions. The chord length and pitch angle distribution were described using Bezier functions. BEM method was used to calculate the aerodynamic performance of the blade. In cause of the research several assumptions were made so as to use a simplified cost effective model. One of those assumptions was that the blade will constitute only 20% of the turbine cost and the turbine cost itself has a linear relationship with weight.
     
     
     
     
    Life cycle assessment of a floating offshore wind turbine
    In this paper the Jan et al. (2009), presents a life cycle assessment (LCA) of electricity generation by a floating offshore wind power plant designed according to a concept of the Norwegian company. The result are compared with Ecoinvent database processes for electricity production in conventional offshore non floating wind power plants and there has been rapid growth in the use of wind power in recent years. In contrast to gas and coal power plants, wind power plants convert wind energy into electricity without significant emission or resource consumption during operation. The preliminary life cycle shows that the environmental impact of electricity production from a floating wind power plant does not differ much with the conventional offshore wind power plant, except for the toxic emissions from material production. Marine ecotoxicity has not been investigated due to lack of appropriate methods and have not collected data on direct marine emissions connected to the installation and maintenance of the power plant. This is a significant gap given to the location of the power plant (offshore).
     
    Wind Blade Chord and twist angle Optimization by using genetic algorithms
     J. Mendez et al (2005), present a method to obtain optimal chord and twist distributions in wind turbines blades by using genetic algorithms. The distributions are computed to maximize the mean expected power depending on the Weibull wind distribution at a specific site because I wind power systems optimization is highly site dependent. This approach avoids assumptions about optimal attack angle related to the ration between the lift to drag coefficients. To optimize chord and twist distributions, an efficient implementation of the Blade-Element and Momentum theory is used. In the implementation, the sophistication is dismissed to reduce computational cost. The time required to evaluate the forces in a typical turbine is in the order of milliseconds, which allows massive evaluation of trial turbines. The implementation is validated by comparing power prediction with the experimental data of the Riso test turbine. High quality in results is obtained until the stall zone, about wind speed of 13m/s proximately.
     
    Testing basic performance of a very small wind turbine designed for multipurpose
    In this paper H. Hirahara et al (2005), the relations among the energy output, turbine speed, power coefficient and torque of turbine were reported for various flow conditions. Then in order to examine the performance, the details of flow field around the turbines and the influences of the turbines were investigated with a particle image velocimetry (PIV) in an environmental wind tunnel. The micro wind turbine was design for use in or near urban space and for multipurpose. The requirements for running are to be quiet, safety in the running and simple for installation. A unique and very small wind turbine, µF500mm diameter was developed for wide use in urban space. The basic performance of µF500 was tested for various free stream and load resistance. The air flow around the turbine was investigated by using a Particle Image Velocimetry (PIV).
     
    Design and Analysis of Horizontal Axis Wind Turbine Rotor
    Arvind et al.(2011), presents an optimization model for rotor design of 750 KW horizontal axis wind turbine. The authors classified loads on a wind turbine as: aerodynamics blade loads, gravity loads on the rotor blades, aerodynamic drag forces on nacelle and tower, gyroscopic loads caused by the yaw motion, centrifugal forces and coriolis forces during the rotor rotation. The focus on the study was the loads affecting the blades which are aerodynamics and gravity loads. A mathematical model and user interface computer program for aerodynamic design of Horizontal Axis Wind Turbine rotor base on type approval provision scheme TAPS-2000 Calculates loads, stress and deflection in wind turbine components. The  HAWT rotor is formulated as a constrained of multi-objective optimization problem with respect to: geometric and operational characteristics, as maximization of output generated, minimization of generated vibration, minimization of blade material cost, minimization of stress and deflection in rotor fulfillment of appropriate strength requirement, by the blade structure.
     
     
    Modeling and Simulation of wind generator with fixed speed wind turbine under Matlab-Simulink
    The work published by Djohra et al, (2012),  was to represent the dynamic behavior of the wind energy conversion system (WECS) allowing power quality characterization, the developed model consist of subsystems such as wind turbine, related block, drive train system, asynchronous machine, Park transformers, three phase grid and the inverse park transformers. The paper inferred that to convert wind power into electricity, several concepts of generators have been used and proposed. Main wind turbine generators can be grouped into two classes: Variable and fixed speed. The fixed speed wind turbine has the advantage of being simple, robust, reliable and well proven. Statistical analysis of the result was performed to test the quality of the fit to the experimental data; Root mean square error (RMSE), the mean bias error and the mean absolute error (MAE) are the fundamental level of accuracy using calculated power or Cp and the experimental power or Cp. After validating the developed model used and in order to verify its usefulness, a study of its behavior when integrated in whole power system was needed. Three level wind speeds were chosen: low with 5m/s as the mean value, medium with 8m/s as the mean value and high with 12m/s as. These allowed predicting and supervising the active power supervise by the system, characterized respectively by the middle powers of -150kw, -250kw and -450kw which will be injected directly into public electricity grid and the reactive power; characterized respectively by the middle powers of  60KW, 180KW and 320KW which are consumed by the wind generator.
     
     
    Computational Fluid Dynamic Simulation of an Innovative system of wind power generation
    S. Carcangiu et al, (2011), proposes an innovative system for wind generation in urban areas. The generation system substitute the roof of the building and it consists of a static part, the stator, and a moving part called impeller or rotor which is a centripetal turbine with vertical axis of rotation. A Logarithmic spiral is chosen as the shape of the stator blades this is to help convey air inflow while avoiding the formation of vortices. The wind flow around and inside the building model is described by Navier-Stoke equations that has been solved for the velocity field and pressure. Nonlinearity momentum and continuity equations were also use. The boundary conditions applied to the computational domain are an inlet boundary condition of velocity vector normal to the boundary of U.n=5m/s which is the mean value of wind in most of Italian territory where the study was carried out. The outlet boundary condition was set as specific pressure of Po=0Pa. A no slip boundary condition of U=0 is set to the ground and the walls of the building. Also symmetry condition applied to the upper boundary, so velocity perpendicular to the boundary was set to zero. The FEM analysis are performed using Comsol Multiphysis, the shape of the duct describe in this study allows for meaningful increase of velocity in the minimum section.
     
     
     
    Computer Aided Design and Performance Analysis of HAWT Blades
    Emrah Kulunk, Nadir Yilmaz (2009).  In the paper presents a methodology using BEM theory for aerodynamic design of HAWT blades, performance analysis of existing blades and using this method to design to design a 100KW HAWT. According to the authors, BEM theory refers to the determination of wind turbine blade performance by combining the equations of general momentum theory and blade element theory. The aerodynamic design of optimum rotor blades from a known airfoil types means determining the geometric parameters such as chord length distribution and twist distribution along the blade length for a certain tip-speed ratio at which the power coefficient of the rotor is minimum. The result obtained shows that for the particular blade, S809 aerofoil at low values of angle of attack, the aerofoil successfully produces a large amount of lift with little drag and at around α=16 a phenomenon known as stall occurs where there is a massive increase in drag and a sharp reduction in lift.
     
    Horizontal Axis Wind Turbine aerodynamics: Three dimensional, unsteady, and separated flow influences
     Accurate and reliable prediction of wind turbine aerodynamics remains a unique challenge for today’s computational modelers stated the authors and that these are due to numerous influences ranging from how rapid changes in wind speed or direction dynamically alter the local angle of attack along the span, to effect of angle of attack and dynamic pressure change due variable speed or pitch variation.  M. C Robinson et al, (1999). points clearly that most wind turbine structural design codes rely on Blade Element Momentum Theory (BEMT) to simulate blade aerodynamic performance and this algorithm allow the aerodynamic model to run quickly, enabling practical design trade-off analysis. However the use of empirical two dimensional wind tunnel test data to obtain a quasi-static aerodynamic loads and necessary assumption associated with BEMT prevents these models form Capturing full three dimensional effects. In studying the three-dimensional performance effects, pressure coefficients (Cp) variation over a rotational cycle was used to provide a metric of the increased blade loading due to three dimensional dynamic responses. Conclusively, the authors inferred that improved understanding of complex wind turbine aerodynamics formalized in accurate robust models will constitute a powerful capability for analyzing and designing wind energy machines for the future.
     
     
     
    Characterization of the Unsteady Flow in the Nacelle Region of a Modern Wind Turbine.
     
    F. Zahle et al (2009), uses 3D Navier-Stokes solver to investigate the flow in the nacelle region of a wind turbine where anemometers are typically placed to measure the flow speed and the turbine yaw angle. A 500 kW turbine was modeled with rotor and nacelle geometry in order to capture the complex separated flow in the blade root region of the rotor. A number of steady state and unsteady simulations were carried out for wind speeds ranging from 6 m/s to 16 m/s as well as two yaw and tilt angles. The flow in the nacelle region was found to be highly unsteady, dominated by unsteady vortex shedding from the cylindrical part of the blades which interacted with the root vortices from each blade, generating high velocity gradients.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
    CHAPTER III
     
    METHODOLOGY
     
    3.1  LITERATURES
    The work on this projects starts with a review of some literatures on the horizontal axis wind turbine.  The literature was group into aerodynamic performance and modeling   analysis and CFD methodologies that has been applied on the HAWT. The individual literatures where summarized and all the literatures reviewed were summarized collectively, it also contain the problem statement, objectives and scope of work that will be carried out in the project.
     
    3.2  AERODYNAMICS OF THE WIND TURBINE
    This section starts with analytical calculations of the energy in the wind; the maximum available power in the wind is calculated in this process. This is followed by analysis of the Blade using momentum theory, particularly the actuator disc model will be use to determine the maximum efficiency that can be achieved under optimal conditions. Next the power and trust coefficients are calculated (the lift and drag coefficients). Finally more advanced method such as the blade element theories and the blade element and momentum theories will be applied in analyzing the blade design.
     
    3.3  CFD SIMULATION USING ANSYS FLUENT
    This section, Computational fluid dynamics analysis will be carried out on the  wind turbines blade. First the blade will be mesh using ansys pre and save as a file format for Fluent simulation. Ansys fluent will then be use to analyze the flow on the blade. The  analysis will be carried out for a test blade,  and then for two blades. Solidworks flow simulation will then be use for flow analysis of the entire HAWT.
     
    3.4  RESULT ANALYSIS AND CONCLUSION
     The result obtained in the previous section will be presented. Comparison will be made with of existing results and conclusion drawn from the project. The section will also include recommendation for further research.
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
    Initial Result
     The result presented below are just one of the initial results that has been obtain so far up till now in the project this
    CHAPTER IV
     
    ANALYSIS USING ANSYS FLUENT

     
    The model geometry is imported to ansys pre for preprocessing settings

                                                         Figure 3.1  rotor with 2 blades          
     To mesh the model, the following settings is done, the type of mesh is chosen