The objective of the current work is to experimentally investigate the effect of turbulent flow on an airfoil with a Gurney flap. The wind tunnel experiments were performed for the DTU-LN221 airfoil under different turbulence level (T.I. of 0.2%, 10.5% and 19.0%) and various flap configurations. The height of the Gurney flaps varies from 1% to 2% of the chord length; the thickness of the Gurney flaps varies from 0.25% to 0.75% of the chord length. The Gurney flap was vertical fixed on the pressure side of the airfoil at nearly 100% measured from the leading edge. By replacing the turbulence grille in the wind tunnel, measured data indicated a stall delay phenomenon while increasing the inflow turbulence level. By further changing the height and the thickness of the Gurney flap, it was found that the height of the Gurney flap is a very important parameter whereas the thickness parameter has little influence. Besides, velocity in the near wake zone was measured by hot-wire anemometry, showing the mechanisms of lift enhancement. The results demonstrate that under low turbulent inflow condition, the maximum lift coefficient of the airfoil with flaps increased by 8.47% to 13.50% (i.e., thickness of 0.75%), and the Gurney flap became less effective after stall angle. The Gurney flap with different heights increased the lift-to-drag ratio from 2.74% to 14.35% under 10.5% of turbulence intensity (i.e., thickness of 0.75%). However, under much a larger turbulence environment (19.0%), the benefit to the aerodynamic performance was negligible.

No abstract

To study the output power and wake flow characteristics of a wind turbine with swept blades, taking the blade tip offset and the location of the sweep start as two variables, the straight blade of the DTU-LN221 baseline airfoil was optimally designed with sweep. Then the designed wind turbine was numerically simulated, and the swept blade with the best optimal output power characteristics was selected for the wind tunnel test. The results indicate that for both forward and backward swept blades, increasing the blade tip offset and the sweep start location could decrease the power and thrust coefficients. Compared with the backward swept design, the forward swept design significantly improved the blades’ power characteristics. By adopting swept blades instead of straight blades, wind turbines could generate more power at high tip speed ratios, especially in yaw conditions. The streamwise velocity recovery of the wind turbine with swept blades was slower than that with straight blades as the lateral velocity near the wake region was higher than that with straight blades. Besides, the wind turbine with swept blades had a greater turbulence intensity of the wake near the wake center than that with straight blades with or without yaw condition.

No abstract