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Numerical and experimental analysis of aerodynamics of a Savunius vertical axis wind turbine

Number of pages: 86 File Format: word File Code: 32576
Year: Not Specified University Degree: Master's degree Category: Biology - Environment
Tags/Keywords: Aerodynamics - Fluid dynamics - Numerical analysis - Numerical simulation - torque - Turbine performance - Vertical axis wind turbine - wind energy - wind turbine
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  • Summary of Numerical and experimental analysis of aerodynamics of a Savunius vertical axis wind turbine

    Dissertation for receiving the master's degree "M.Sc"

    Mechanical engineering - energy conversion trend

    Abstract

    In this thesis, an experimental analysis along with numerical simulation has been done to investigate the performance of the Sawnius vertical axis wind turbine.  In order to carry out the tests, the turbine was tested in the subsonic wind tunnel. In order to check the accuracy of the experiments, each experiment was repeated three times at each wind speed, and the results were in good agreement with each other. Numerical simulation has been done with the help of Fluent 6.3 software using the k-? SST model and using the multiple reference coordinate axes (MRF) method. Torque, power factor, stress and pressure distribution on turbine blades have been studied. In order to check the validity and accuracy of the numerical results obtained from the principles of Computational Fluid Dynamics (CFD), comparison with the experimental results of the wind tunnel has been used. The results indicate that the numerical and experimental results are in good agreement, and there is a 6% error between our results in the maximum amount of error at the maximum point of the power factor. Numerical results showed that static pressure and shear stress increase with increasing angular speed and also wind speed.

    Key words: wind energy, Savunius vertical axis wind turbine, computational fluid dynamics, torque, power factor.

    1 Introduction Due to the global desire to reduce greenhouse gases and provide sustainable energy that meets the ever-increasing human need for all kinds of energy, many efforts are being made to develop renewable energies. Wind energy, as one of the most reliable types of energy, has an ancient history, and its use in order to build huge power plants has seen a significant boom in recent decades. This has led to many studies on various types of wind turbines. In this chapter, an introduction to wind energy and some practical and required concepts about wind power and wind farms are explained. We will also take a look at the state of installed capacity of wind power plants in the world from the past until now, as well as the forecast of the state of wind power until 2017. At the end, we will explain the purpose of this thesis and the chapters in it.

    1-2 The origin of wind

    The origin of wind is a complex issue. Since the earth is unevenly heated by sunlight, therefore there is less thermal energy in the poles than in the equatorial regions, and temperature changes occur more quickly in the luminaries, and therefore the land of the earth warms up and cools down faster than the seas. This global temperature difference will create a global heat exchange system that extends from the Earth's surface to the atmosphere of the globe, acting as an artificial roof. Most of the energy contained in the movement of wind can be found in the upper levels of the atmosphere where the sustained wind speed reaches more than 160 kilometers per hour and eventually the wind loses its energy due to friction with the surface of the earth and the atmosphere.

    A general estimate says that there are 72 terawatts (TW) of wind energy on earth that has the potential to be converted into electrical energy, and this amount is also renewable.

    In the same way, the big atmospheric winds that go around the earth are created because the surface air near the equator is heated more by the heat of the sun than the air at the north and south poles. Since the wind will be produced continuously as long as the sun shines on the earth, it is called a renewable energy source. Today, wind energy is mainly used to generate electricity.

    1-3 History of Wind

    Throughout history, humans have used wind in various ways. More than 5,000 years ago, the ancient Egyptians used the power of the wind to propel ships on the Nile. After that, man built a windmill to grind his seed.. The newest windmill belongs to Iran. This mill resembled very large paddles.

    Centuries later, the Dutch improved the basic design of the windmill. They added propeller-like blades made from new vanes to the windmill and devised a way to change its direction according to the direction of the wind. Windmills helped the Dutch to be the most industrialized country in the world in the 17th century. The turbine has been tested in a subsonic wind tunnel. Experimental results are repeated three times to check the accuracy of the test apparatus. Also, a numerical study is done using the software Fluent 6.3 using k-? SST model and based on moving reference frame (MRF) method. To check the robustness of the numerical results, they are compared with experimental data. The comparison shows excellent agreements between both experimental and numerical results with maximum 6% error. Moment, power coefficient, shear stress and static pressure are considered. Results illustrate that, shear stress and static pressure increase with velocity magnitude and angular velocity.

    Keywords: Wind Energy, Savonius Vertical Axis Wind Turbines, Computational Fluid Dynamics, Moment, Power Coefficient.

  • Contents & References of Numerical and experimental analysis of aerodynamics of a Savunius vertical axis wind turbine

    List:

     

    The first chapter. 13

    1-1 Introduction. 14

    1-2 source of wind. 14

    1-3 History of wind. 15

    1-4 Wind speed distribution. 16

    1-5 wind sources. 17

    1-6 Wind production. 18

    1-7 capacity factor. 20

    1-8 periodic restrictions and influence. 21

    1-9 predictability. 22

    1-10 wind and environment. 22

    1-11 Spread of pollution. 23

    1-12 wind farms. 24

    1-12-1 land use. 24

    1-13 Small-scale wind power. 25

    1-14 wind energy potential in urban environments. 26

    1-15 The status of wind power in the world. 27

    1-16 issues discussed in the thesis, objectives and how to conduct the research. 29

    The second chapter. 31

    2-1 Introduction. 32

    2-2 Turbine aerodynamics and quantities affecting its performance. 32

    2-2-1 drag force 32

    2-2-2 drag force 33

    2-2-3 Reynolds number 36

    2-2-4 turbine rigidity. 36

    2-2-5 blade tip speed coefficient. 36

    2-2-6 efficiency and power of wind turbines. 37

    2-3 types of wind turbines. 38

    2-3-1 Horizontal axis turbines. 39

    2-3-2 vertical axis turbines. 44

    3-1 Introduction. 53

    3-2 Turbine construction. 53

    3-2-1 Construction of Saunius turbine. 54

    3-3 Turbine test in wind tunnel. 57

    3-4 How to place the turbine in the tunnel for testing. 62

    3-5- Test results. 63

    The fourth chapter. 67

    4-1 Introduction. 68

    4-2 Preprocessor. 69

    4-3 Mathematical model. 69

    4-4 Production of computing cells. 70

    4-5 mesh resolution. 73

    4-6- Mesh quality. 74

    4-7 smoothness of cells 75

    Chapter five. 76

    5-1 Introduction. 77

    . 77

    5-2 Boundary conditions in Fluent software. 77

    5-2-1 Output and input flow. 78

    5-2-2 wall boundary condition 79

    5-2-3 fluid condition. 79

    5-2-4 Boundary conditions used. 79

    3-5 Equations of motion. 80

    5-5 Modeling turbulent flows. 81

    5-6 Reynolds averaged Navirastox equations (RANS) 82

    5-7 Standard k-? model. 85

    5-8 k-? SST model. 87

    5-9 computational area and boundary conditions. 87

    5-10 convergence of the solution. 88

    5-11 Selection of solution methods. 89

    5-12 Power calculation. 90

    5-13 Numerical results. 91

    5-13-1 Checking independence from the network. 91

    5-13-2 Comparison of numerical and laboratory results. 92

    5-13-3 pressure distribution 93

    5-13-4 shear stress distribution. 94

    5-13-5 Speed ??contours. 97

    Sixth chapter. 100

    6-1 Conclusion. 101

    6-2 suggestions. 101

    References. 103

     

    Source:

     

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    [2] United Nations Environment Program, “Global Trends in Sustainable Energy Investment”, 2009

    [3] American Wind Energy Association, “Global Wind Energy Market Report”,

    http://www.awea.org/pubs/documents/globalmarket2003.pdf March 7, 2010.

    [4] Global Wind Energy Council, “Global Wind 2009 report”,

    http://www.gwec.net/index.php?id=78 June 2010.

    [5] S. Eriksson, H. Bernhoff, and M. Leijon. "Evaluation of different turbine concepts for wind power" Renewable and Sustainable Energy Reviews, vol. 12, pp. 1419-1434,2008.

    [6] Golding, E. W., “The Generation of Electricity by Wind Power”, London E. & F. M. Spon Ltd, Halsted Press, 1976.

    [8] Global Wind Energy Council, www.gwec.net.

    [9] Betz, A., “Das Maximum der theoretisch moglichen Ausnutzung des Windes durch Windmotoren”, Zeitscrift fur das gesamte Turbinenwesen, Heft 26, Sept.26, 1920.

    [10] Manwell, J. F., McGowan, J. G., Rogers, A. L., “Wind Energy Explained; Theory, Design and Application”, John Wiley & Sons Ltd, 2002.

    [11] Savonius SJ. The S-rotor and its applications; Mech Eng, 53, 333–8, 1931. [12] Gupta R, Das R, Sharma KK. Experimental study of a Savonius-Darrieus wind machine. In: Proceedings of the international conference on renewable energy forIn: Proceedings of the international conference on renewable energy for developing countries, 2006.

    [13] Debnath, B.K.; Biswas, A.; Gupta, R., "Computational fluid dynamics analysis of a combined three-bucket Savonius and three-bladed Darrieus rotor at various overlap conditions". Journal of Renewable and Sustainable Energy, 1, 033110-14, 2009.

     

    [14] Betz, A., “Das Maximum der theoretisch moglichen Ausnutzung des Windes durch Windmotoren”, Zeitscrift fur das gesamte Turbinenwesen, Heft 26, Sept.26, 1920.

    [15] Manwell, J. F., McGowan, J. G., Rogers, A. L., “Wind Energy Explained; Theory, Design and Application", John Wiley & Sons Ltd, 2002. [16] Menet JL.  A double-step Savonius rotor for local production of electricity: a design study.  Renew  Energy  ;29:1843–62, 2004.

     

    [17] Akwaa, J. V., Vielmob, H.A., Petryb, A.P., A review on the performance of Savonius wind turbines; Renewable and Sustainable Energy Reviews 16, 3054–3064, 2012.

    [18] B. Altan, M. At?lgan, An experimental and numerical study on the improvement of the performance of Savonius wind rotor, Energy Conversion and Management 49 (2008) 3425-3432.

    [19] M.H. Mohamed, G. Janiga, E. Pap, D. Thévenin, Optimal blade shape of a modified Savonius turbine using an obstacle shielding the returning blade, Energy Conversion and Management 52 (2011) 236–242.

     

    [20] M. Kamoji, S. Kedare, S. Prabhu, Experimental investigations on single stage modified Savonius rotor, Applied Energy 86 (2009) 1064-1073.

     

    [21] T. Hayashi, Y. Li, Y. Hara Wind tunnel tests on a different phase three-stage Savonius rotor. JSME Int J, Ser B: Fluids Therm Eng, 48(1) (2005) 9-16.

    [22] Saha UK, Thotla S, Maity D. Optimum design con?guration of Savonius rotor through wind tunnel experiments;  J Wind Eng Ind Aerod,96,1359-75, 2008. [23] N. Fujisawa, K. Ishimatsu, K. Kage, A comparative study of Navier-Stokes calculations and experiments for the Savonius rotor, Journal of Solar Energy Engineering 117 (1995) 344-346.

    [24] T. Kawamura, T. Hayashi, K. Miyashita, Application of the domain decomposition method to the flow around the Savonius rotor, In: Proc. of the 12th International conference on Domain Decomposition Methods, 2001, pp. 393-400.

     

    [25] R.Gupta, B. Debnath, R. Das, CFD analysis of a two-bucket Savonius rotor using Fluent package. In: Proc. of the European Wind Energy Conference, 2009. [26] Islam, M., Ting, D. S.-K. and Amir, F., "Aerodynamic Models for Darrieus-type Straight-bladed, Vertical Axis Wind Turbines", Renewable and Sustainable Energy Reviews, Vol. 12, No. 4, pp. 1087-1109, 2008.  

     

    [27] Sivasegaram, S. and Sivapalan, S., “Augmentation of Power in Slow-Running Vertical-axis Wind Rotors Using Multiple Vanes”, Wind Engineering, Vol. 7, No. 1, pp. 12-19, 1983. [28] Takao, M., Maeda, T., Kamada, Y., Oki, M., Kuma, H., "A Straight-bladed Vertical Axis Wind Turbine with a Directed Guide Vane Row", Proceedings of 5th Joint ASME/JSME Fluids Engineering Conference, San Diego, USA, Paper No. FEDSM2007-37422, 2007. [29] Kuma, H., Takao, M., Beppu T., Maeda, T., Kamada, Y, and Kamemoto, K., “A Straight-bladed Vertical Axis Wind Turbine with a Directed Guide Vane– Mechanism of Performance Improvement”, Proceedings of 27th International Conference on Offshore Mechanics and Arctic Engineering, Estoril, Portugal, Paper No. OMAE2008-57233, 2008. [30] M. Hiroyuki Takita et al, Experimental study of a straight-bladed vertical axis wind turbine with a directed guide vane row, Proceedings of the ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering, Honolulu, Hawaii, USA, OMAE2009 May 31 - June 5. 2009. [31] Guerri, O

Numerical and experimental analysis of aerodynamics of a Savunius vertical axis wind turbine
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