Experimental Study on Aerodynamic Characteristics of a Gurney Flap on a Wind Turbine Airfoil under High Turbulent Flow Condition

Abstract

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.

Experimental Study of a Gurney Flap on a Pitching Wind Turbine Airfoil under Turbulent Flow Conditions

“…This conclusion was consistent with our previous static experiment that the Gurney flap has better aerodynamic performance at a moderate T.I. inflow condition [38].…”

“…This conclusion was consistent with our previous static experiment that the Gurney flap has better aerodynamic performance at a moderate T.I. inflow condition [38]. Figure 9 shows the lift hysteresis loops in the deep stall region under three turbulent inflow conditions.…”

“…In order to further illustrate the possible validity of the conclusions in this paper on a full-size wind turbine, it was necessary to be concerned about the Reynolds effect. Based on similar research [37], Figure 4b exhibited the lift coefficient results measured in uniform flow conditions [29,38] to reflect the possible relation. It can be found that when the Re was 1.5×10 5 , there was an approximate relationship between the lift coefficients with a higher Re, so the Reynolds effect was not evident in this experiment.…”

Special Issue on Wind Turbine Aerodynamics II

“…Subsequently, the effects of wind shear were also studied for the turbine with a tilt angle of 4 • , and it was found that wind shear will cause the thrust and power of the wind turbine to decrease. Yang et al [8] experimentally studied the effect of Gurney flaps on the performance of a wind turbine airfoil (DTU-LN221 airfoil [9]) under different turbulence levels (T.I. of 0.2%, 10.5%, and 19.0%) and various flap configurations.…”

Study on Turbulence Intensity Behavior under a Large Range of Temperature Variation

“…Nishi et al studied the environmental and boundary layer of a wind tunnel to control turbulence characteristics [9]. Kelberlau et alestimated the TI with a continuous wave wind lidar [10], and Yang et al studied the aerodynamic characteristics of a gurney flap in turbulence level (TI of 0.2%, 10.5%, and 19.0%) [11].…”