The aerodynamic design of horizontal-exis wind turbines

perpendicular to drag force. So, the extraction of a significant amount of energy from a flow has to be connected with unsteady flow phenomena. For this reason, the choice of referance frame is important. The flow through a steadily rotating horizontal-axis turbine in a reference frame attached to earth is steady, even when the oncoming flow is steady. When the turbine is considered in a reference frame attached to the turbine blade, the flow is steady, but it rotates as a whole around an axis coinciding with the axis of the turbine. Since there are aerodynamic forces experienced by the turbine blades, it is evident that there must be a circulation of the flow around them. From this point of the view, the flow around the turbine can be rep resented by vortex lines, like done for a wing. There are two kinds of vortex lines representing the turbine. One of them is the bound vortex which is running along the blade from its root to tip. The other kind is trailing vortex which is running helically along the rotation axis from all points of the blades to infinity. This vortex system induces velocities in front of, at and behind the rotor. With the effect of these induced velocities, the axial velocity increases and the tangential velocity decreases continiously along the rotation axis. For a detailed calculation, the rotor is represented by an infinite number of blades. This assumption makes the flow axissymetric and a homogenous circulation distribution at all definite radial stations. So, all quantities are independent from the angular coordinate. The cylindrical wake is examined, as well as the expanding wake. Even in the case of cylindrical wake, the equations representing the flow field are non-linear and the calculation of induced velocities is very complicated. They can only be calculated for some special cases. But the analysis gives important results. For example, the Bernoulli constant and circulation are constant along a stream surface. This result is used to carry the far behind flow conditions to the rotor plane. The calculation for constant circulation along the span shows that the rotation of wake decreases the power output. Since an exact solution of the influence of wake expansion with the circulation concept is very complicated, momentum considerations can be used. Axial momentum equation is applied to the stream tube and the outher flow separatly and angular momentum equation is applied to xiSUMMARY THE AERODYNAMIC DESIGN OF HORIZONTAL-AXIS WIND TURBINES The kinetic energy of the atmosphere is enormous. The idea to make use of this energy is very old. But the availability of the fossil fuels and the invention of electric engine prevented the development of wind turbines some time in the past. The energy chrisis of 1974 led to a renewed and lasting interest in alternative energy resources, like water, solar energy and wind energy. Today many researches about wind energy are carried out in different countries. The purpose of a wind turbine is to get mechanical energy from wind, then to turn it into electric energy. This kind of energy has some superiorities like being clean and unlimited. The electric energy from the wind does not need to be carried. However, it's true that wind energy is intermittent with respect to oil and nuclear power. In the present work, attention is only limited to fluid dynamics as pect; Firstly, the meteorological effects and the wind energy potential are mentioned briefly. The winds of the earth depend on the effect of unequal heating of the earth's surface by the sun, with the principle of "heated air rises". Since the earth's surface has a rough topographic shape, the mag nitude and the direction of the winds are changable. For this reason, most studies on the available amount of wind energy start with a kind of wind energy prospecting close to the ground, based on available meteorological IXperpendicular to drag force. So, the extraction of a significant amount of energy from a flow has to be connected with unsteady flow phenomena. For this reason, the choice of referance frame is important. The flow through a steadily rotating horizontal-axis turbine in a reference frame attached to earth is steady, even when the oncoming flow is steady. When the turbine is considered in a reference frame attached to the turbine blade, the flow is steady, but it rotates as a whole around an axis coinciding with the axis of the turbine. Since there are aerodynamic forces experienced by the turbine blades, it is evident that there must be a circulation of the flow around them. From this point of the view, the flow around the turbine can be rep resented by vortex lines, like done for a wing. There are two kinds of vortex lines representing the turbine. One of them is the bound vortex which is running along the blade from its root to tip. The other kind is trailing vortex which is running helically along the rotation axis from all points of the blades to infinity. This vortex system induces velocities in front of, at and behind the rotor. With the effect of these induced velocities, the axial velocity increases and the tangential velocity decreases continiously along the rotation axis. For a detailed calculation, the rotor is represented by an infinite number of blades. This assumption makes the flow axissymetric and a homogenous circulation distribution at all definite radial stations. So, all quantities are independent from the angular coordinate. The cylindrical wake is examined, as well as the expanding wake. Even in the case of cylindrical wake, the equations representing the flow field are non-linear and the calculation of induced velocities is very complicated. They can only be calculated for some special cases. But the analysis gives important results. For example, the Bernoulli constant and circulation are constant along a stream surface. This result is used to carry the far behind flow conditions to the rotor plane. The calculation for constant circulation along the span shows that the rotation of wake decreases the power output. Since an exact solution of the influence of wake expansion with the circulation concept is very complicated, momentum considerations can be used. Axial momentum equation is applied to the stream tube and the outher flow separatly and angular momentum equation is applied to xiSUMMARY THE AERODYNAMIC DESIGN OF HORIZONTAL-AXIS WIND TURBINES The kinetic energy of the atmosphere is enormous. The idea to make use of this energy is very old. But the availability of the fossil fuels and the invention of electric engine prevented the development of wind turbines some time in the past. The energy chrisis of 1974 led to a renewed and lasting interest in alternative energy resources, like water, solar energy and wind energy. Today many researches about wind energy are carried out in different countries. The purpose of a wind turbine is to get mechanical energy from wind, then to turn it into electric energy. This kind of energy has some superiorities like being clean and unlimited. The electric energy from the wind does not need to be carried. However, it's true that wind energy is intermittent with respect to oil and nuclear power. In the present work, attention is only limited to fluid dynamics as pect; Firstly, the meteorological effects and the wind energy potential are mentioned briefly. The winds of the earth depend on the effect of unequal heating of the earth's surface by the sun, with the principle of "heated air rises". Since the earth's surface has a rough topographic shape, the mag nitude and the direction of the winds are changable. For this reason, most studies on the available amount of wind energy start with a kind of wind energy prospecting close to the ground, based on available meteorological IXperpendicular to drag force. So, the extraction of a significant amount of energy from a flow has to be connected with unsteady flow phenomena. For this reason, the choice of referance frame is important. The flow through a steadily rotating horizontal-axis turbine in a reference frame attached to earth is steady, even when the oncoming flow is steady. When the turbine is considered in a reference frame attached to the turbine blade, the flow is steady, but it rotates as a whole around an axis coinciding with the axis of the turbine. Since there are aerodynamic forces experienced by the turbine blades, it is evident that there must be a circulation of the flow around them. From this point of the view, the flow around the turbine can be rep resented by vortex lines, like done for a wing. There are two kinds of vortex lines representing the turbine. One of them is the bound vortex which is running along the blade from its root to tip. The other kind is trailing vortex which is running helically along the rotation axis from all points of the blades to infinity. This vortex system induces velocities in front of, at and behind the rotor. With the effect of these induced velocities, the axial velocity increases and the tangential velocity decreases continiously along the rotation axis. For a detailed calculation, the rotor is represented by an infinite number of blades. This assumption makes the flow axissymetric and a homogenous circulation distribution at all definite radial stations. So, all quantities are independent from the angular coordinate. The cylindrical wake is examined, as well as the expanding wake. Even in the case of cylindrical wake, the equations representing the flow field are non-linear and the calculation of induced velocities is very complicated. They can only be calculated for some special cases. But the analysis gives important results. For example, the Bernoulli constant and circulation are constant along a stream surface. This result is used to carry the far behind flow conditions to the rotor plane. The calculation for constant circulation along the span shows that the rotation of wake decreases the power output. Since an exact solution of the influence of wake expansion with the circulation concept is very complicated, momentum considerations can be used. Axial momentum equation is applied to the stream tube and the outher flow separatly and angular momentum equation is applied to xi