The Method Of Adjusting The Wind Energy Absorption Rate By Changing The Length Of The Wind Blade

Because of the tendency of capacity of Wind Turbine and the length of blade kept growing, as the core component of a wind turbine, the blade plays a vital role in this field, its stability and sensitivity, the adjustability of efficiency and the range of Power generation directly impact the running condition of the generation set, the complexity of the electricity part, the equality of the power and the access area of wind power. Besides the quality of the blade itself, the most important factor to keep the set running smooth is the blade's stability and sensitivity.Analyze the modern method for efficiency adjustments, there is no theory for adjusting efficiency by changing the blade's parameters itself. Such as installing a brake on the former edge of blade can only be used in the smaller wind turbine rather the large one, like Pitch-Regulated Device, it produces the extra Vibration on blade which even lower the stability, unlike the joint adjustment, the Independent Pitch-Regulated Device is not ready practically and coming the higher cost. Or like yaw system, which is usually not considered to be the method for efficiency adjustment, is basically activated as emergency. Therefore, a new adjustment method which directly affect the blade itself is needed. Within the advantage of higher sensitivity, this method can co-operate with other adjustments without any conflicts on equipment installation and etc.With this particular goal, this paper analyze the fault of classical one-dimensional momentum theory for failing to explain the difference of the flow field when the parameters of the blade change. Therefore, on the basic of the theory, the Plate model is improved to be the Single Blade Area-limited Model, and by using the mass conservation for the blade's front-side and the back-side to express the flow field. Base on this new model, the theory of the flow field changing pattern is built by varied area of the blade, and provides the theoretical support for the method of Blade chord length adjustment. The basic research result is as follows:1. By Analyzing the Single Blade Area-limited Model's expression for flow field, this paper built The Dispersed Mass Model, the field movement on both sides of the blade can be described through the mutative kinetic energy carried by infinitesimal mass fluid. Using the mass conservation law, using mass superposition vector to avoid complex velocity calculation, and deduced equation of velocity and equation of blade thrust for Flow Field, by the theory of momentum conservation and conservation of kinetic energy.2. Refer to the Boundary Layer theory, this paper find that the kinetic energy transmitting inside the flow can be neglected, therefore the velocity field of the surface, where the particular blade element is, is equivalence to the velocity field of this blade element itself. In order to discuss the space relation from two theories of one same blade, this paper built three coordinate systems:one for turbine; one for blade, and last one for blade element, which is generated by twisting blade's pitch angle.3. Discuss the necessary condition for best performance of turbine blade. Based on the experienced formulation, this paper choose one airfoil as blueprint, and designed a varied chord length twisted blade, calculate the shape parameters by conformal transformation theory. Use software to analyze the lift-drag force characteristic for particular parameters of airfoil by choosing different Reynolds number, and calculate the chord length and twist angle distribution. Eventually, using existing Blade design theory to examine the results.4. Assuming the output torque of the blade don't change when wind velocity changing, this paper calculate the necessary chord length, which will ensure the tangential force of the blade. Compare the chord length changing ratio to the wind velocity changing ratio, finally build the blade efficiency adjustment theory, which will alter the length of chord in order to change the blade efficiency, so the blade output torque will remain steady.