The aerodynamic design of the blade is mainly the shape optimization design, which is a crucial step in the blade design. The advantages and disadvantages of the blade airfoil design in the shape optimization design directly determine the power generation efficiency of the wind turbine. Under the operating conditions of the wind turbine, the flowing Reynolds number is relatively low. The blades usually operate at low speed and high lift coefficient. The flow interference between the blades causes the flow. very complicated. In view of the complex flow state of the blade shape and the distribution of the blade profile in different directions, the design of the blade profile becomes very important.
At present, the design technology of blade profile usually adopts advanced aircraft wing airfoil design method in aviation to design the shape of blade profile. Advanced CFD technology has been widely used in the design of different types of aerodynamic shapes. For fan operating conditions under low Reynolds number and high lift coefficient, it is necessary to analyze the flow field of the blade profile by using the N-S control equation considering the viscosity.
In the past 10 years, the horizontal axis wind turbine blade airfoil usually chooses NACA series aviation airfoils, such as NACA44XX, NA-CA23XX, NACA63XX and NASALS(1). These airfoils are very sensitive to the roughness of the leading edge. Once the leading edge becomes rough due to pollution, the airfoil performance will be greatly reduced, and the annual output power loss can reach up to 30%. After recognizing that aviation airfoils are not suitable for wind power blades, after the mid-1980s, developed countries in wind power began to study special airfoils for blades and successfully developed special airfoil series for wind power blades, such as the US Seri and NREL series, and Denmark. RISO-A series, Swedish FFA-W series and Dutch DU series.
These airfoils have their own advantages. Seri series have low sensitivity to airfoil surface roughness; RISO-A series have good stall performance when approaching a stall and have low sensitivity to leading edge roughness; FFA-W series have good rear surface roughness. Stall performance. Danish LM company has adopted the Swedish FFA-W airfoil for large wind turbine blades, and the special airfoil for wind turbines will be widely used in the design of wind power blades.
At present, there are several design theories for blade shape, all of which are developed on the basis of wing aerodynamic theory. The first shape design theory is a simplified design method based on the Bates theory. This method assumes that the wind turbine is operating under the best conditions of the Bates formula, without considering eddy current loss, etc., and the designed wind turbine efficiency does not exceed 40%.
Later, some famous aerodynamicists established their own blade aerodynamic theory. Schmitz theory considers the vortex loss in the circumferential direction of the blade, and the design result is relatively accurate. Glauert theory considers the vortex flow behind the wind wheel, but ignores the influence of blade airfoil resistance and blade loss, which has a small effect on the shape of the blade, but has a greater impact on the efficiency of the wind turbine. Wilson made improvements on the basis of Glauert theory, studied the influence of blade loss and lift-to-drag ratio on the best performance of the blade, and studied the performance of the wind wheel under non-design conditions, which is currently the most commonly used design theory.
