In the figure below, the blades are listed in eight positions from 0 degrees to 315 degrees. The wind enters from the left. The light blue vector v is the wind speed and the green vector u is the linear speed. inverse speed of the direction of the circular movement of the blade (i.e. the speed of the air flow felt by the blade when there is no wind), the blue vector w is the speed of the resultant airflow experienced by the blade (i.e. relative wind speed), and the purple vector L is the lift force experienced by the blade.
Let's analyze the stress exerted on the blades at these eight angles. At positions of 90 degrees and 270 degrees, relative wind speed does not produce lift. At the other six positions, the lift received by the blades. can all move. The steering produces a torque force, which is why the Darieu wind turbine can rotate under the force of the wind.
In fact, the situation is much more complicated. THEPrevious analysis diagram is an ideal state, that is, the state in which the ideal tip speed ratio and no blade resistance are present. The torque force used by the blades to push the rotor to turn is the component of the combined lift and drag force in the forward direction of the blades. Let's take the situation at 315 degrees to analyze the situation with resistance. The black vector D in the figure is the resistance experienced by the blades. The brown vector F is the combined force of lift L and resistance D. The component force M of this. The force in the forward direction of the blades is M. This is the actual torque force. Obviously, the torque force at this time is significantly lower than the ideal condition.
And at angles near 180 degrees and 270 degrees, the combined force of lift and drag produces an inverse torque force.
The Darieux wind turbine has a greater output force onlyuement when the blades are close to 360 degrees and 180 degrees. Even so, it can only work when the top speed ratio is greater than 3.5. This can be illustrated by the following figure.
In the figure on the left, the blade is affected by the relative wind speed W with respect to the blade. generate the lift L and the drag D. The angle between the relative wind speed W and the chord line of the blade, that is to say the angle of attack α of the blade, is approximately 14 degrees. The relative wind speed W is composed of the wind speed. V and the blade movement speed u. At this time, the blade moving speed is about 4 times the wind speed, that is, the peak speed ratio is 4. The resulting force of lift L and resistance D is F, and the moment of force exerted by this force on the wind wheel is M, which is the force that turns the wind wheel. When the speed ratio de tip is 4, the blade can generate a moment to push the rotor when it operates on the windward or leeward side. Only near both sides (90 degrees and 180 degrees), the lift force is very weak and there will be some. a small negative directional impact.
The wind speed on the right side of the figure has doubled, but the speed of movement of the blade has not changed. The tip speed ratio is approximately 2 and the blade angle of attack α is approximately. 27 degrees. At this time, the blade operates in a stall state, the lift L generated by the blades decreases considerably, but the resistance D increases considerably. The moment of force M generated by the wind wheel is negative, which prevents rotation. of the wind wheel. At this time, the blades generate negative moments in most positions. For the most common airfoils, when the tip speed ratio is less than 3.5, the blades will not produceThere is virtually no force to push the rotor to turn.
It is difficult for the Darrieu wind turbine to operate under low wind speeds. Only under higher wind speeds can the wind turbine rotate normally when the blade tip speed ratio reaches 3.5 or more.
, higher power output can be obtained when the tip speed ratio is 4 to 6. In order to reduce drag and increase lift, the cross-sectional shape of the wind turbine blades is The shape selection requirements (aerodynamic profile) and surface finish are relatively high. Since the Darieu wind turbine cannot rely on lift when the tip speed ratio is less than 3.5, can it operate in drag? Since each fin is fixed uniformly around the circumference of the wind wheel, the moment of resistance generated by each fin due to the wind is not grand and the total moment combined by each aileron is very small even though some moment can be generated at any given time. From a certain angle, it cannot be generated from another angle. A reverse torque is generated, so the Darieu wind turbine cannot start automatically by wind power alone. It must be started by external force so that the blade tip speed ratio reaches more than 3.5 forward. can work with an elevator. The typical wing of the Darieu wind turbine is not straight, but curved, and the two wings form a φ shape. The image below shows a Darieux wind turbine model.
Today's Darieu wind turbines mainly use straight blades, which some call H-shaped wind turbines. The number of blades in H-type wind turbines is generally 2 to 6.
The blades of Darieu wind turbines are fixed on the rotating shaft from both ends or the middle, which is beneficial for increasingr mechanical resistance. and can be made very light; Darieux wind turbine is not heavy, has lower tower requirements, is suitable for fixing with cables, is easy to install, and is convenient for maintenance. These are its advantages. Regarding the problem that the Darieu wind turbine cannot start automatically, the general method is to use a generator as a motor to drive the wind turbine rotating during starting, so that the blade tip speed ratio reaches more than 3 ,5. Due to the strict requirements for wind speed changes and load changes, it is difficult to operate smoothly and efficiently, and due to the inconvenience of not being able to start automatically, the development of Darieu n wind turbines 'has been slow in recent years. after technical improvements, it began to grow significantly.
To analyze the paerodynamic performance of the wind wheel, it is necessary to understand the flow field at the wind wheel in order to analyze the aerodynamic force, torque and power generated. For this, an aerodynamic model of the lift-type wind turbine must be established.
Operating principle of the wind turbine (the future of renewable energies)
Principle of electricity production
Convert The kinetic energy of wind energy wind into mechanical kinetic energy, and then convert the mechanical energy into electrical kinetic energy, which is the production of wind energy. The principle of wind power generation is to use wind energy to rotate the blades of the wind turbine, then use a speed multiplier to increase the rotation speed to induce the generator to produce electricity.
According to current wind turbine technology, electricity production can start ata breeze speed of about three meters per second (the degree of breeze). Wind energy is becoming a craze worldwide because it does not require the use of fuel and does not produce radiation or air pollution.
Due to the unstable air volume, the wind turbine produces 13-25V alternating current, which needs to be rectified by the charger, and then the battery is charged, so that the electrical energy generated by the wind turbine is converted into chemical energy. Then use an inverter with a protection circuit to convert the chemical energy of the battery into AC 220V mains power to ensure stable use.
Detailed information:
1. Horizontal axis wind turbine, the rotation axis of the wind wheel is parallel to the wind direction;
2. The wind wheel is perpendulum to the ground or to the direction of the air flow.
Advantages:
1. Clean environmental benefits;
2. Renewable and never exhausted
3. is short and can be built on land or at sea;
4. The installed capacity is flexible and the operation and maintenance costs are low.
Baidu Encyclopedia - Wind Energy
Wind turbine is a device that uses wind energy to convert it into electrical energy. It drives a generator to produce electricity through the rotation of a wind turbine. The working principle of a wind turbine mainly includes three processes: wind energy conversion, mechanical energy conversion and electrical energy conversion.
1. Wind energy conversion
Wind is the result of atmospheric movement on Earth and has enormous energy. The process of converting wind turbines using wind energy consist to convert wind energy into kinetic energy on the wind wheel. When the wind blows through the rotor of the wind turbine, the rotor rotates due to the force of the wind.
2. Mechanical energy conversion
The rotation of the wind wheel will cause the rotor inside the generator to rotate. The rotor is made up of magnets and coils. As the rotor turns, the magnetic field also changes. According to Faraday's law of electromagnetic induction, changes in the magnetic field will induce an electromotive force in the coil. This electromotive force is transmitted to the generator output through the wire, forming an electric current.
3. Conversion of electrical energy
The current transmitted through the wire will then be converted into electrical energy via the transformer. Transformers convert low voltage current into high voltage current so that electrical energy can be supplied more efficientlyicamentally. Ultimately, electrical energy is transmitted via transmission lines to users for their use.
Steps of wind turbine operation
1 Site selection
Site selection of wind turbines is very important. Generally speaking, you should choose an area with high and stable wind speeds to ensure that the wind turbine can continue to produce electricity. At the same time, it is also necessary to consider the surrounding environmental factors, such as the impact of terrain, buildings, etc. on the wind.
2. Installation Foundation
Once the site selection has been determined, the installation of the wind turbine foundation must be carried out. This includes work such as digging foundation pits and pouring concrete. The stability of the foundation is crucial to the normal operation of wind turbines.
3. Install the wind wheel and generator
A foIf the foundation is installed, the wind wheel and generator must be installed on the foundation. Wind rotors generally consist of several blades that must be installed perpendicular to the wind direction to maximize the use of wind energy.
4. Connect the transmission lines
After the installation is completed, the wind turbine must be connected to the transmission lines. This requires wiring and connection work. Ensuring the reliability and security of connections is essential to the transport of electrical energy.
5. Operation and Monitoring
After completing the installation and connection, the wind turbine motor is now ready to operate. At the same time, operational monitoring is necessary to detect and resolve possible problems in a timely manner to ensure the normal operation of wind turbines.