Aerodynamic performance of discrete trailing edge flaps of wind turbine airfoil

Abstract: In order to increase the wind capture ability of the wind turbine, many research studies on the lift enhancement method of the wind turbine airfoil have been conducted by scholars at home and abroad. An airfoil with tailing edge flaps has a much higher lift-to-drag ratio than an airfoil without trailing edge flaps. Among all the lift enhancement methods of trailing edge flaps, the structure of the wind turbine airfoil with discrete trailing edge flaps is simple, the cost of production is low, and it can easily achieve variable angle control. But the aerodynamic performance of the wind turbine airfoil with traditional discrete trailing edge flaps has not been comprehensively studied, and gaps between the flaps and the airfoil main body has an influence on the aerodynamic performance of the airfoil. So it is necessary to optimize the gap structure and study the aerodynamic performance of the discrete trailing edge flaps with different deflection angles. Taking a wind turbine airfoil S809 as the research object, the structure of the discrete trailing edge flaps was designed, the chord length was set as 1 000 mm, and the gap between the flap and the main body of airfoil was optimized to make the width of gap an even 1 mm. Then the trailing edge flaps model was established. The flap rotates around the rotate center to form a different flap model at different deflect angles, the deflect angles of the flap varied from 0-16°, and the step size was 2. Mesh generation software Gambit s used to generate a model mesh, and the grids near the trailing edge were refined. After comparing the three kinds of grid number models, the grid independence was verified, and the number of a 148000 grid model for a calculating model was determined. The k-ω two equation turbulence model of Commercial software FLUENT was used here to calculate the aerodynamic performance of the airfoil S809 without flaps, and the result was compared with the experimental data. The result showed that when the attack angle is small ,the error of lift coefficient is less than 0.9%, the error of drag coefficient is less than 4.86%, and the pressure coefficient distributions of calculated model is in good agreement with the experimental data. All these data verified that the calculated method was right and reliable. And then the aerodynamic performance of the 10% chord length flaps with different deflection angle under the attack angle of 0° was studied with the same method. The pressure contours, streamline and pressure coefficient distribution around the model with discrete trailing edge flaps were calculated and analyzed theoretically. The result showed that the gaps between the flap and the main body of airfoil were reasonably designed, and that the gaps had little influence on the aerodynamic performance of the airfoil. So the influence of the gaps can be ignored here. The deflect angle of the discrete trailing edge flaps had much influence on the aerodynamic performance of the model. With the increase of the deflect angle, the camber of airfoil was increased, this made the airflow near trailing edge of airfoil deflected downward, the velocity of airflow near the upper surface of airfoil increased, this result in the pressure of the upper surface of airfoil decreased, and the pressure of the lower surface of airfoil decreased, then the pressure difference between the upper and lower surface was also increased, eventually leading to enhancement of the lift coefficient and the lift-to-drag ratio of the airfoil with discrete trailing edge flaps. When the deflection angle was 14°, the lift-to-drag ratio of the airfoil reached the highest. The drag of the airfoil decreased with the increase of attack angle at first and then increased with the increase of attack angle. When the attack angle was 4°, the drag was the smallest.