Energy is one of the most major fields in the development of a society and its economy. Its consummations rate could by the way be an indicator of the level of prosperity that a nation could achieve. Among renewable sources of energies, hydro power is an important source of environmental-friendly energy and has become more and more important in the recent years. Water energy, as a renewable source of energy, can help in reducing the dependency on fossil fuels. The number of installed water power systems is increasing every year and many nations have made plans to make large investments in hydropower in the near future. Many developed and developing countries have realized the importance of water as an important resource for power generation and necessary measures are being taken up across the globe to tap this energy for its effective utilization in power production. Remarkable advances in water turbines design have been possible due to developments in modern technology. In this context, we are interested in developing a design and a numerical study of the Impulse and the Cross flow hydro turbine‘s type. This book contains four chapters; in the first, a bibliographic study has been developed in order to present a general view about renewable energy, hydropower and different ways to gather it. A particular interest has been given to the water rotors concerning their different types and historical of some famous type like cross flow and Impulse turbines type, object of our study. Indeed, the bibliographic study summarized the considered parameters to improve the water turbine performances. The second chapter presents the numerical approach developed using the CFD code "CFX". I present also the mathematical formulation and the turbulence model will be presented. Then a background of the used methods in our numerical model will be undertaken. The third chapter presents the numerical simulations consisting on the characterization of the hydro dynamic structure of the impulse and the cross flow turbines The fourth chapter consist of the design of the test bench and the different components and solutions.
Table of content
Introduction
Chapter 1: Bibliographic research
1. Introduction
2. Renewable energy
2.1. Why should we use Renewable Energy?
2.2. What’s a renewable energy?
3. Hydropower
3.1. Hydroelectricity
3.2. Generating methods
3.2.1. Conventional dams
3.2.2. Pumped-storage hydroelectricity
3.2.3. Run-of-the-river hydroelectricity
3.2.4. Tidal power
3.3. Underground power station
4. Water turbine
4.1. Francis turbine
4.2. Kaplan turbine
4.3. Tyson turbine
4.4. Gorlov helical turbine
4.5. Impulse turbines
4.6. Horizontal wheel
4.7. Breast shot wheel
4.8. Overshot wheel
4.9. Reversible wheel
4.10.Back shot wheel
4.11. Peiton wheel
5. Efficiency calculation
5.1. Pressure measurement
6. Conclusion
Chapter 2: Numerical model
1. Introduction
2. CFD methodology
2.1. Creating the Geometry/Mesh
2.2. Solving the CFD Problem
2.3. Visualizing the Results in the Postprocessor
3. Mathematic formulation
3.1. Mass Conservation
3.2. Momentum Conservation
3.3. Volume of Fluid Model
3.4. Turbulence models
3.4.1. k-8 model
3.4.1.1 Standard k-8 model
3.5. Realizable k-ε model
3.6. RNG k-ε model
3.7.1. SSTk-ω Model
3.8. Standard k-ω model
4. Finite Volume Method
5. Convergence Criteria
6. Conclusion
Chapter 3: Numerical simulations
1. Introduction
2. Impulse turbine
2.1. Meshing
2.2. Boundary conditions
2.3. Volume fraction
2.4. Velocity vectors
2.6 Dynamic pressure
2.7. Turbulent kinetic energy
2.8. Torque value
2.9. Efficiency
3. Cross flow turbine
3.1. Meshing
3.2. Boundary conditions
3.3. Volume fraction
3.4. Velocity vectors
3.5. Static pressure
3.6. Dynamic pressure
3.7. Turbulent kinetic energy
3.8. Efficiency
4. Study of the test section
4.1. Meshing
4.2. Boundary conditions
4.3. Velocity vectors
4.4. Static pressure
4.5. Dynamic pressure
4.6. Turbulent kinetic energy
4.7. Volume fraction
5. Conclusion
Chapter 4: Design of the test bench
1. Introduction
2. Test bench components
2.1. Turbine choice
2.2. Turbine box
2.3. Tank
2.4. Tank support
2.5. Water pump
2.6. Collector
3. Instrumentation
3.1 Torque meter
3.2. Rotation speed measurement
3.3. Alternator bearing system
3.4. Electricity production
3.5. Pitot tube
4. Test bench presentation
4.1. Advantages
4.2. Disadvantages
4.3. System installation
5. Steel rod section and thickness
5.1 Tank support
5.2. Turbine
6. Conclusion
Conclusion and perspectives
Reference
Dedication
First arud foremost, to my dearpareruts Mohamed arud Souhlr sources of ту joys, sec-rets of my streruøth. you will always be the model: x>ad in your determlruatloru, your streruøth arud horuesty arud Mom Iru your øoodruess, Ljour patleruce arud ljour devotion to me. Tharute you for all ljour sacrifices■ so that ! proøress. without you I would ruever arrlch this level. Tharute you for slavlruø away without rest, despite the vicissitudes of life. Tharute you to be simply my pareruts. I have to offer this Worte arud I avu ■proud to offer it To my sisters wíj deru arud yesmlrue, thejewel of the family, I dedicate this Worte with you all my best wishes for happlruess, health arud success. Arud ! will express my feellruøs of respect arud love.
Nermlrue who ruever stopped bellevlruø Iru me .who has beeru so close to me that I found her with me wheruever I rueeded. she Is my ruearest surrender arud has provided me with a stroruø love shield that always ruever let aruy sadness enter Iruslde. I caru't find the just arud sincere words to express my affection, love
arud respect, you are my life.
To my dear friends, to my famlly, to all those I love.
Ahmed
Acknowledgement
It is with great pleasure that I write these few lines to show gratitude and appreciation to all those who contributed to the development of this project.
I would like to show my appreciation to the supervisor Mr. Zied DRESS.
I want to express appreciation to the members of the juries: Mr. Lasaad Walha and Mr. Slim Triki and who agreed to judge this work.
I thank all those who contributed directly or indirectly to the development of this work.
We warmly welcome all distinguished teachers and technicians of our prestigious mechanical engineering department of the ENIS.
Nomenclature
Abbildung in dieser Leseprobe nicht enthalten
Figures list
Figure 1.1. Projected Renewable Production (Hernandez-Escobedo et al. 2011)
Figure 1.2. Global renewable power capacity excluding hydro
Figure 1.3. Saint Anthony falls, United States
Figure 1.4. Three Gorges Dam-China (2009)
Figure 1.5. Cross section of a conventional hydroelectric dam
Figure 1.6. Diagram of the TVA pumped storage facility
Figure 1.7. Chief Joseph Dam near Bridgeport, Washington
Figure 1.8. A tidal stream generator Sea Gen
Figure 1.9. An underground power station
Figure 1.10. Examples of waterturbines
Figure 1.11. Francis turbine
Figure 1.12. Vertical Kaplan turbine
Figure 1.13. Tyson turbine
Figure 1.14. Gorlov helical turbine
Figure 1.15. Impulse turbine
Figure 1.16. Undershot water wheel
Figure 1.17. Breast shot wheel
Figure 1.18. Overshot water wheel
Figure 1.19. Reversible wheel
Figure 1.20. Overshot water wheel
Figure 1.21. Peiton turbine
Figure 1.24. Schematic representation of fluid flow pattern at location of IT AB AR profile .
Figure 1.25. Velocity triangle
Figure 2.1. ANSYS CFX File Types
Figure 2.2. Control volume
Figure 2.3. Convergence algorithm
Figure 3.1. Control volume
Figure 3.2. Meshing
Figure 3.2. Boundary conditions
Figure 3.3. Turbine box Volume fraction
Figure 3.4. Velocity vectors
Figure 3.5. Static pressure
Figure 3.6. Dynamic pressure during turbine rotation
Figure 3.7. Distribution of the turbulent kinetic energy
Figure 3.8. Distribution of the torque
Figure 3.9. Torque values for different rotating speed
Figure 3.10. Impulse turbine efficiency
Figure 3.11. Rotating domain
Figure 3.12. Meshing
Figure 3.13. Boundary conditions
Figure 3.13. Distribution of the volume fraction
Figure 3.14. Velocity vectors
figure 3.15. Static pressure
Figure 3.16. Distribution of the dynamic pressure
Figure 3.17. Distribution of the turbulent kinetic energy
Figure 3.18. Cross flow turbine efficiency
Figure 3.19. Geometrical arrangement
Figure 3.20. Meshing effect
Figure 3.21. Meshing parameters
Figure 3.22. Boundary conditions
Figure 3.23. Velocity vectors in the test section
Figure 3.24. Distribution of the static pressure
Table 3.25. Dynamic pressure distribution
Table 3.26. Distribution of the turbulent kinetic energy
Figure 4.1. Turbine
Figure 4.3. Roller
Figure 4.3 Tank choice
Figure 4.5. Tank support choice
Figure 4.6. Water pump
Figure 4.7. Cylindrical collector
Figure 4.8. Torque meter
Figure 4.9. Torque meter installation
Figure 4.10. Digital laser tachometer position
Figure 4.11. Flexible coupling
Figure 4.12. Pitot tube
Figure 4.13. Pitot tube position for the two turbines
Figure 4.14. Testbench
Figure 4.15. System installation on building
Figure 4.16. Simulation specification
Figure 4.17. Support generator simulation results
Figure 4.18. Simulation results
Figure 4.19. Impulse turbine simulation results
Figure 4.20 Cross flow turbine vectors simulation
Figure 4.21. Cross flow turbine simulation results
General introduction
Introduction
Energy is one of the most major fields in the development of a society and its economy. Its consummations rate could by the way be an indicator of the level of prosperity that a nation could achieve. Among renewable sources of energies, hydro power is an important source of environmental-friendly energy and has become more and more important in the recent years. Water energy, as a renewable source of energy, can help in reducing the dependency on fossil fuels. The number of installed water power systems is increasing every year and many nations have made plans to make large investments in hydropower in the near future. Many developed and developing countries have realized the importance of water as an important resource for power generation and necessary measures are being taken up across the globe to tap this energy for its effective utilization in power production. Remarkable advances in water turbines design have been possible due to developments in modern technology. In this context, we are interested in developing a design and a numerical study of the Impulse and the Cross flow hydro turbine‘s type.
This book contains four chapters; in the first, a bibliographic study has been developed in order to present a general view about renewable energy, hydropower and different ways to gather it. A particular interest has been given to the water rotors concerning their different types and historical of some famous type like cross flow and Impulse turbines type, object of our study. Indeed, the bibliographic study summarized the considered parameters to improve the water turbine performances.
The second chapter presents the numerical approach developed using the CFD code "CFX". I present also the mathematical formulation and the turbulence model will be presented. Then a background of the used methods in our numerical model will be undertaken.
The third chapter presents the numerical simulations consisting on the characterization of the hydro dynamic structure of the impulse and the cross flow turbines
The fourth chapter consist of the design of the test bench and the different components and solutions.
Finally, we present a general conclusion of this work and the outlook suggested by this study.
Chapter 1: Bibliographic study
1. Introduction
With the rapid development of the global economy, energy requirements have increased remarkably, especially in emergent countries. The realization that fossil fuel resources required for the generation of energy are becoming scarce and that climate change is related to carbon emissions to the atmosphere has increased interest in energy saving and environmental protection (Vine et al., 2008). The first strategy to reduce dependence on fossil resources is based on reducing energy consumption by applying energy savings programs focused on energy demand reduction and energy efficiency in industrial (Lee and Chen, 2009) and domestic (Martiskainen et al., 2010) fields’ spheres.
2. Renewable energy
A second strategy to achieve this goal consists of using renewable energy sources, not only for large-scale energy production, but also for stand-alone systems (Zhou et al.2010). Renewable energy technologies are known to be less competitive than traditional electric energy conversion systems, mainly because of their intermittency and the relatively high maintenance cost. However, renewable energies avoid the safety problems derived from atomic power (Strupczewskim et al.2003), which is why, from the social point of view, it has become more desirable to adopt renewable energy power plants (Skoglund et al.2010). An important decision for governments and businesses is whether or not to establish renewable energy systems in a given place and to decide which renewable energy source or combination of sources is the best choice. Several authors have evaluated the main renewable energy technology taking into account sustainability indicators, such as Evans et al. (Evans et al.2009). The improvement of renewable energy technologies will assist sustainable development and provide a solution to several energy related environmental problems. In this sense, optimization algorithms constitute a suitable tool for solving complex problems in the field of renewable energy systems. Figure 1.1 shows that this technique has a couple of shortcomings. First, it aggregates all renewable energy sources: geothermal, solar, wind, biomass etc. Because some of these sources are still in their infancy, it is possible that they may exhibit higher growth rates in the future, thus making the projection too conservative. Balancing this of course is the possibility that they may run into unexpected constraints, skewing the outcome in the other direction. The second problem is that due to the youth of the industry large discontinuities in production from year to year may render the curve fit unreliable.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.1. Projected Renewable Production (Hernandez-Escobedo et al. 2011)
2.1. Why should we use Renewable Energy?
Energy is a vital input for social and economic development. As a result of the generalization of agricultural, industrial and domestic activities the demand for energy has increased remarkably, especially in emergent countries. This has meant rapid grower in the level of greenhouse gas emissions and the increase in fuel prices, which are the main driving forces behind efforts to utilize renewable energy sources more effectively, i.e. energy which comes from natural resources and is also naturally replenished. Despite the obvious advantages of renewable energy, it presents important drawbacks, such as the discontinuity of generation, as most renewable energy resources depend on the climate, which is why their use requires complex design, planning and control optimization methods. Fortunately, the continuous advances in computer hardware and software are allowing researchers to deal with these optimization problems using computational resources, as can be seen in the large number of optimization methods that have been applied to the renewable and sustainable energy field.
2.2. Whaťs a renewable energy?
Renewable energy is energy which comes from natural resources such as sunlight, wind, rain, tides and geothermal heat, which are renewable, with 10% coming from traditional biomass, which is mainly used for heating, and 3.4% from hydroelectricity. New renewable (small hydro, modern biomass, wind, solar, geothermal, and biofuels) accounted for another 3% and are growing very rapidly. The share of renewable in electricity generation is around 19%, with 60% of global electricity coming from hydroelectricity and 3% from new renewable. Wind power is growing at the rate of 30% annually, with a worldwide installed capacity of 238.000 megawatts (MW) at the end of 2011, and is widely used in Europe, Asia, and the United States. At the end of 2011 the photovoltaic (PV) capacity worldwide was 67.000 MW and PV power stations are popular in Germany and Italy. Solar thermal power stations operate in the USA and Spain, and the largest of these is the 354 megawatts (MW) SEGS power plant in the Mojave Desert. The world largest geothermal power installation is the Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving injection of ethanol fuel from sugarcane, and ethanol now provides 18% of the country’s automotive fuel. Ethanol fuel is also widely available in the USA. Figure 1.2 shows an exponential evolution of the global renewable power capacity excluding hydro from 2004 to 2011. While many renewable energy projects are large-scale, renewable technologies are also suited to rural and remote areas, where energy is often crucial in human development. As 2011 small solar PV systems provide electricity to a few million households, and micro-hydro configured into mini-grids serves many more. Over 44 million households use biogas made in household-scale digesters for lighting and/or cooking and more than 166 million households rely on a new generation of more-efficient biomass cook stoves. United Nations secretary- General Ban Ki- moon has said that renewable energy has the ability to lift the poorest nations to new levels of prosperity. Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization. New government spending, regulation and policies helped the industry weather the global financial crisis better than many other sectors. According to a 2011 projection by international Energy Agency, solar power generators may produce most of the world’s electricity within 50 years, dramatically reducing the emissions of greenhouse gases that harm the environment.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.2. Global renewable power capacity excluding hydro
3. Hydropower
Hydropower, hydraulic power, hydrokinetic power or water power is power that is derived from the force or energy of falling water, which may be harnessed for useful purposes. Since ancient times, hydropower has been used for irrigation and the operation of various mechanical devices, such as watermills, sawmills, textile mills, dock cranes, and domestic lifts. Since the early 20th century, the term is used almost exclusively in conjunction with the modem development of hydro-electric power, the energy of which could be transmitted considerable distance between where it was created to where it was consumed. Another previous method used to transmit energy had employed a tromp, which produces compressed air from falling water, which could then be piped to power other machinery at a distance from the energy source. Water's power is manifested in hydrology, by the forces of water on the riverbed and banks of a river. When a river is in flood, it is at its most powerful, and moves the greatest amount of sediment. This higher force results in the removal of sediment and other material from the riverbed and banks of the river, locally causing erosion, transport and, with lower flow. Taking into account the fact that water is much denser than air, even a slow flowing stream of water, or moderate sea swell can yield considerable amounts of energy.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.3. Saint Anthony falls, United States
3.1. Hydroelectricity
As more and more countries deregulate their electricity market, new challenges appear for hydroelectricity producers. To maximize their profits, they now need to consider market price uncertainty in their production plan. This IS much more complex than maximizing the total production when prices are constant. Hydroelectricity is the term referring to electricity generated by hydropower; the production of electrical power through the use of the gravitational three of falling or following water. It is the most widely used form of renewable energy, accounting for 16 percent of global electricity consumption, and 3,427 terawatt-hours of electricity production in 2010, which continues the rapid rate of increase experienced between 2003 and 2009. Hydropower is produced in 150 countries, with the Asia-Pacific region generating 32 percent of global hydropower in 2010. China is the largest hydroelectricity producer, with 721 terawatt-hours of production in 2010, representing around 17 percent of domestic electricity use. There are now three hydroelectricity plants larger than 10 GW: the Three Gorges Dam in China, ltaipu Dam in Brazil, and Guri Dam in Venezuela. The cost of hydroelectricity is relatively low, making it a competitive source of renewable electricity. The average cost of electricity from a hydro plant larger than 10 megawatts is 3 to 5 D.s. cents per kilowatt-how. Hydro is also a flexible source of electricity since plants can be ramped up and down very quickly to adapt to changing energy demands. However, damming interrupts the flow of rivers and can harm local ecosystems, and building large dams and reservoirs often involves displacing people and wildlife and requires significant amounts of carbon-intensive cement. Once a hydroelectric complex is constructed, the project produces no direct waste, and
has a considerably lower output level of the greenhouse gas carbon dioxide (C02) than fossil fuel powered energy plants.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.4. Three Gorges Dam-China (2009)
3.2. Generating methods
3.2.1. Conventional dams
Most hydroelectric power comes from the potential energy of dammed water driving a water turbine and generator. The power extracted from the water depends on the volume and on the difference in height between the source and the water's outflow. This height difference is called the head. The amount of potential energy in water is proportional to the head. A large pipe (the "penstock") delivers water to the turbine.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.5. Cross section of a conventional hydroelectric dam
3.2.2. Pumped-storage hydroelectricity
Pumped-storage hydroelectricity is a type of hydroelectric power generation used by some power plants for load balancing. The method stores energy in the form of water, pumped from a lower elevation reservoir to a higher elevation. Low-cost off-peak electric power 15 used to run the pumps. During periods of high electrical demand, the stored water IS released through turbines to produce electric power. Although the losses of the pumping process makes the plant a net consumer of energy overall, the system increases revenue by selling more electricity during periods of peak demand, when electricity prices are highest. Pumped storage is the largest-capacity form of grid energy storage now available. It can be 70% to 87% efficient in practice.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.6. Diagram of the TVA pumped storage facility
3.2.3. Run-of-the-river hydroelectricity
Run-of-the-river hydroelectricity (ROR) is a type of hydroelectric generation whereby a considerably smaller water storage called bondage or none is used to supply a power station. Run-of-the-liver power plants are classified as with or without bondage. A plant without bondage has no storage and is, therefore, subjected to seasonal liver flows and serves as a peaking power plant while a plant with bondage can regulate water flow and serve either as a peaking or base load power plant. Run-of-the-river hydroelectricity is ideal for streams or rivers with a minimum dry weather flow or those regulated by a much larger dam and reservoir upstream. A dam, smaller than that used for traditional hydro, is required to ensure that there is enough water to enter the "penstock" pipes that lead to the lower-elevation turbines. Projects with bandage, as opposed to those without bandage, can store water for peak load demand or continuously for base load, especially, during wet seasons. In general, projects divert some or most of a river's flow (Thor S-E et al.2006) up to 95% of mean annual discharge) through a pipe and/or tunnel leading to electricity -generating turbines, then return the water back to the river downstream, projects are dramatically different in design and appearance from conventional hydroelectric projects. Traditional hydro dams store enormous quantities of water in reservoirs, necessitating the flooding of large tracts of land. In contrast, most run-of-river projects do not require a large impoundment of water which is a key reason why such projects are often referred to as environmental ly-friendly, or "green power." The use of the term “run- of-the-river" for power projects varies around the world and is dependent on different definitions. Some may consider a project ROR if power is produced with no storage while a limited storage is considered by others. Developers may mislabel a project ROR to sooth public image about its environmental or social effects. The Bureau of Indian Standards describes run- of-the-river hydroelectricity as a power station utilizing the run of the river flows for generation of power with sufficient bondage for supplying water for meeting diurnal or weekly fluctuations of demand. In such stations. The normal course of the river is not materially altered. Many of the larger ROR projects have been designed to a scale and generating capacity rivaling some traditional hydro dams. For example, one ROR project currently proposed in British Columbia (BC) Canada has been designed to generate 1027 megawatts capacity.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.7. Chief Joseph Dam near Bridgeport, Washington
3.2.4. Tidal power
Tidal power, also called tidal energy, is a form of hydropower that converts the energy of tides into useful forms of power - mainly electricity. Although not yet widely used, tidal power has potential for future electricity generation. Tides are more predictable than wind energy and solar power. Among sources of renewable energy, tidal power has traditionally suffered from relatively high cost and limited availability of sites with sufficiently high tidal ranges or flow velocities, thus constricting its total availability. However, many recent technological developments and improvements, both in design (e.g. dynamic tidal power, tidal lagoons) and nu-bine technology (e.g. new axial turbines, cross flow turbines), indicate that the total availability of tidal power may be much higher than previously assumed, and that economic and environmental costs may be brought down to competitive levels. Historically, tide mills have been used, both in Europe and on the Atlantic coast of North America. The earliest occurrences date from the Middle Ages, or even from Roman times. The world's first Large- scale tidal power plant (the Ranke Tidal Power Station) became operational in 1966.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.8. A tidal stream generator Sea Gen
3.3. Underground power station
An underground power station makes use of a large natural height difference between two waterways, such as a water fall or mountain lake. An underground tunnel is constructed to take water from the high reservoir to the generating hall built in an underground cavern near the lowest point of the water tunnel and a horizontal tailrace taking water away to the lower outlet waterway.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.9. An underground power station
4. Water turbine
A water turbine is a rotary engine that takes energy from moving water. Water turbines were developed in the 19th century and were widely used for industrial power prior to elecnical grids. Now they are mostly used for electric power generation. They harness a clean and renewable energy source. Water Wheels have been used for thousands of years for industrial power. Their main shortcoming is size, which limits the flow rate that can be harnessed. The migration from water wheels to modern turbines took about one hundred years. Development occurred during the industrial revolution, using scientific principles and methods. They also made extensive use of new materials and manufacturing methods developed at the time. The word turbine was introduced by the French engineer Claude Bourdin in the early 19th century and is derived from the Latin word for "whirling" or a "Vortex". The main difference between early water turbines and water wheels is a swirl component of the water which passes energy ta a spinning rotor. This additional component of motion allowed the turbine to be smaller than a water wheel of the same power. They could process more water by spinning faster and could harness much greater heads. (Later, impulse turbines were developed which didn't use swirl. Flowing water is directed on the blades of a turbine runner, creating a force on the blades. Since the runner is spinning, the force acts through a distance in this way, energy is transferred from the water flow to the turbine Water turbines divided into two groups; reaction turbines and impulse turbines. The precise shape of water turbine blades is a function often supply pressure of water, and the type of impeller selected.
4.1. Francis turbine
The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts. Francis turbines are the most common water turbine in use today. They operate in a head range of 10 to 650 meters (33 to 2,133 feet) and are primarily used for electrical power production. The power output generally ranges from 10 to 750 megawatts, though mini-hydro installations may be lower. Runner diameters are between 1 and 10 meters (3 and 33 feet). The speed range of the turbine is from 83 to 1000 rpm. Mediun size and larger Francis turbines are most often managed with a vertical shaft. Vertical shaft may a 150 be used for small size turbines, but normally they have horizontal shaft. The Francis turbine is a reaction turbine, which means that the working fluid changes pressure as it moves through the turbine, giving up its energy. A cerement is needed to contain the water flow. The turbine is located between the high-pressure water source and the low-pressure water exit, usually at the base of a dam.
4.2. Kaplan turbine
The Kaplan turbine IS a propeller-type water turbine which has adjustable blades. It was developed in 1913 by the Austrian professor Viktor Kaplan, who combined automatically adjusted propeller blades with automatically adjusted wicket gates to achieve efficiency over a wide range of flow and water level. The Kaplan turbine was an evolution of the Francis turbine. Its invention allowed efficient power production in low-head applications that was not possible with Francis turbines. The head ranges from 10-70 meters and the output from 5 to 120 MW. Runner diameters are between 2 and 8 meters. The range of the turbine is from 79 to 429 rpm. Kaplan turbines are now widely used throughout the world in high-flow, low-head power production. The Kaplan turbine is an inward flow reaction turbine, which means that the working fluid changes pressure as it moves through the turbine and gives up its energy. Power is recovered from both the hydrostatic head and from the kinetic energy of the flowing water.
4.3. Tyson turbine
The Tyson turbine is a hydropower system that extracts power from the flow of water. This design doesn't need a cerement, as it is inserted directly into flowing water. It consists of a propeller mounted below a raft, driving a power system, typically a generator, on top of the raft by belt or gear. The turbine is towed into the middle of a river or stream, where the flow is the fastest, and tied off to shore. It requires no local engineering, and can easily be moved to other locations.
4.4. Gorlov helical turbine
The Gorlovka helical turbine (GHT) is a water turbine evolved from the Darnus turbine design by altering it to have helical blades/foils. It was patented in a series of patents from September 19, 1995 to July 3, 2001 and won 2001 ASME Thomas A. Edison Patent Award. GHT was invented by Professor Alexander M. Gorlovf the Northeastern University. The physical principles of the GHT work are the same as for its main prototype, the Darnus turbine, and for the family of similar vertical axis wind turbines which includes also wind turbine Quiet revolution wind turbine Urban Green Energy. GHT, turbulence and quiet revolution solved torque issues by using the helical twist of the blades.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.14. Gorlov helical turbine
4.5. Impulse turbines
Impulse turbines change the velocity of a water jet. The jet pushes on turbine’s curved blades which changes the direction of the flow. The resulting change in momentum (impulse) causes a force on the turbine blades. Since the turbine is spinning, the force acts through a distance (work) and the diverted water flow is left with diminished energy. Prior to hitting the turbine blades, the water's pressure (potential energy) is converted to kinetic energy by a nozzle and focused on the turbine. No pressure change occurs at the turbine blades, and the turbine doesn't require housing for operation. Newton's second law describes the transfer of energy for impulse turbines. Impulse turbines are most often used in very high head applications.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.15. Impulse turbine
4.6. Horizontal wheel
Commonly called a tub wheel or Norse mill, the horizontal wheel is essentially a very primitive and inefficient form of the modem turbine. It is usually mounted inside a mill building below the working -floor. A jet of water is directed all to the paddles of the water wheel, causing them to turn; water exits beneath the wheel, generally through the center. This is a simple system, usually used without gearing so that the vertical axis of the water wheel becomes the drive spindle of the mill. An undershot wheel (also called a stream wheel) is a vertically-mounted water wheel that is rotated by water striking paddles or blades at the bottom of the wheel. The name undershot comes from this striking at the bottom of the wheel. This type of water wheel is the oldest type of wheel. It is also regarded as the least efficient type, although subtypes of this water wheel allow somewhat greater efficiencies than the traditional undershot wheels. The advantages of undershot wheels are that they are somewhat cheaper and simpler to build, and have less of an environmental impact as they do not constitute a major change of the river. Their disadvantages are as mentioned before less efficiency, which means that they generate less power and can only be used where the flow rate is sufficient to provide torque. Undershot wheels gain no advantage from head. They are most suited to shallow streams in flat country.
Abbildung in dieser Leseprobe nicht enthalten
Figure 1.16. Undershot water wheel
4.7. Breast shot wheel
A vertically-mounted water wheel that is rotated by falling water striking buckets near the center of the wheel's edge, orjust above it, is said to be breast shot. Breast shot wheels are the most common type in the United States of America and are said to have powered the American industrial revolution. Breast shot wheels are less efficient than overshot wheels more efficient than undershot wheels, and are not back shot. The individual blades of a breast shot wheel are actually buckets, as are those of most overshot wheels, and not simple paddles like those of most undershot wheels. A breast shot wheel requires a good trash rack and typically has a masonry "apron" closely conforming to the wheel face, which helps contain the water in the buckets as they progress downwards. Breast shot wheels are preferred for steady, high-volume flows such as are found on the famine of the North American East Coast.
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Figure 1.17. Breast shot wheel
4.8. Overshot wheel
A vertically-mounted water wheel that is rotated by falling water striking paddles, blades or buckets near the top of the wheel is said to be overshot. In hue overshot wheels, the water passes over the top of the wheel, but the term is sometimes applied to back shot or pitch back wheels where the water goes down behind the water wheel. A typical overshot wheel has the water channeled to the wheel at the top and slightly beyond the axis. The water collects in the buckets on that side of the wheel, making it heavier than the other "empty" side. The weight turns the wheel, and the water flows out into the tail-water when the wheel rotates enough to invert the buckets. The overshot design can use all of the water flow for power (unless there is a leak) and does not require rapid flow.
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Figure 1.18. Overshot water wheel
4.9. Reversible wheel
A special type of overshot wheel is the reversible water wheel. This has two sets of blades or buckets running in opposite directions, so that it can turn in either direction depending on which side the water are directed. Reversible wheels were used in tuning industry in order to power various means of one conveyance. By changing the direction of the wheel, barrels or baskets of one could be lifted up or lowered down a shaft. As a rule there was also a cable drum or a chain basket (German: Kettenkorb. 2011) on the axle of the wheel. It was also essential that the wheel had braking equipment in order to be able to stop the wheel (known as a braking wheel). The oldest known drawing of a reversible water wheel was by Georgia’s Agricola and dates to 1556.
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Figure 1.19. Reversible wheel
4.10. Back shot wheel
A back shot wheel (also called pitch back) is a variety of overshot wheel where the water is introduced just behind the summit of the wheel. It combines the advantages from breast shot and overshot systems, since the full amount of the potential energy released by the falling water is harnessed as the water descends the back of the wheel. A back shot wheel continues to function until the water in the wheel pit rises well above the height of the rude, when any other overshot wheel will be stopped or even destroyed. This makes the technique particularly suitable for streams that experience externe seasonal variations in flow, and reduces the need for complex sluice and tail race configurations. A back shot wheel may also gain power from the water's current past the bottom of the wheel, and not just the weight of the water falling in the wheel's buckets.
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Figure 1.20. Overshot water wheel
4.11. Peiton wheel
The Peiton wheel is an impulse turbine which is among the most efficient types of water turbines. It was invented by Lester Allan Peiton in the 1870s. The Peiton wheel extracts energy from the impulse (momentum) of moving water, as opposed to its weight like traditional overshot water wheel. Although many variations of impulse turbines existed prior to Peloton’s design, they were less efficient than Pelton's design; the water leaving these wheels typically still had high speed, and carried away much of the energy. Peloton’s paddle geometry was designed so that when the rim runs all the speed of the water jet the water leaves the wheel with very little speed, extracting almost all of its energy, and allowing for a very efficient turbine. The water flows along the tangent to the path of the runner. Nozzles direct forceful streams of water against a series of spoon-shaped buckets mounted around the edge of a wheel.
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Figure 1.21. Peiton turbine
5. Efficiency calculation
5.1. Pressure measurement
According to the continuity law derived by Bernoulli and the energy equation, the sum of the pressure energy and the potential and kinetic energy of a flowing fluid inside a pipe and in conditions of stationary and frictionless flow is the same at any time and in any part of the pipe.
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The factor p (static) is the static pressure equally distributed in all directions. The other term in the equation represents the dynamic pressure, effective in the flow direction, p (dynamic). For flowing fluids in horizontal pipes, with a small velocity compared to the Mach-number (Ma «1), the dynamic pressure p (dynamic) of a fluid with a flowing velocity V, a density p and a resistance factor ζ is calculated as:
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Inserting a fixed body into a flowing fluid causes the flow to dam up immediately upstream of the body and to be completely zero at S2. At this point, the total pressure p is defined as follow: ps2 = pd + ps (13־)
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Figure 1.24. Schematic representation of fluid flow pattern at location of IT AB AR profile
The efficiency and the pressure (Pout and Pin) are calculated in these formulation below:
Where:
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figure 1.25. velocity triangle
[...]
- Quote paper
- Ahmed Ben Chalbi (Author), 2018, Conception and Numerical Study of the Cross Flow and Impulse Hydroturbine, Munich, GRIN Verlag, https://www.hausarbeiten.de/document/441047
