| Wind turbine dedicated airfoil families were successively developed in order to improve both the aerodynamic and structural requirements. However, there were some differences between the traditional aviation airfoils and the wind turbine dedicated airfoils, such as Reynolds number, angle of attack, the tailing edge thickness, and so on. We should make a special research on the aerodynamic performance of the wind turbine airfoil. Flow separation and stall phenomenon over an airfoil is related to the velocity and pressure distribution. Therefore, the near wall region need to be concentrated. Drag reduction by riblets is the most popular, and its effectiveness is fully valid in aviation area.Firstly, the empirical formula for the smooth flat plate drag coefficient is adopted, which can provide a standard to check the turbulent model’s accuracy. In the near wall region of the streamwise-ribleted plate, viscous sublayer is thickened and the average velocity gradient is small, which lead to the drag reduction. A pair of vortex, equal and opposite in direction, exists at the top of the riblet, and makes the flow remain in the riblet valley. At the same time, the spanwise flow is restricted by the vortexes. Reynolds number, the heitht of riblet h and the h+value are included in the elements that influence the drag reduction ratio. The conclusion is, when the riblet is fixed, the ratio of drag reduction and the value of h+increases as the Reynolds number becomes larger. Different Reynolds number corresponds to various optimal h+, which is not only limited to the existing literature of h+≤25. Secondly, we performed numerical simulation NACA0012. Because of the rather small riblet size and the low Re numbers, the simulation results are not good agreement with the experiment. There is big difference between DU00-W2-401airfoil and symmetric thin airfoil. The former is apt to flow separation even at a small angle of attack. Riblets are arranged at both surface of the DU00-W2-401airfoil. The comparative calculations indicate that riblets only have function on the suction side, and drag reduction appears at higher angles of attack.Thick airfoils are effective measures to improve the wind turbine blade structural properties, but likely to separate which results in aerodynamic efficiency loss. Install a ring spoiler at the maximum chord position of1.5MW wind turbine blade under the condition of not changing the blade structure characteristics, and make the CFD calculation. Spoiler can indeed improve the flow condition on the blade surface by truncating the spanwise flow forcely and guiding the fluid along the chordwise, and mitigate the adverse pressure gradient near the spoiler. The influence on flow field mainly concentrates in the nearby region behind the spoiler. Spoiler brings the wind turbine annual generation in a0.58%increase.The CAS closed return flow low speed wind tunnel was tested, and the pressure distribution of S809airfoil was measured. The insufficient expansion of CAS wind tunnel makes the result has a little difference with CSU. Smooth and ribleted airfoil section experiments are conducted separately by the surface pressure measuring system, seven-hole probe and boundary layer probe. Riblets make the drag coefficient increase at small angles of attack, while reduce at higher angles. |
PDF Full Text Request