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.
Highlights
Wind power generation technology has been maturely developed in the past decades
Two types of grilles generate different turbulence levels in the wind tunnel, such that the experiments were mainly separated into different turbulence levels in the wind tunnel, such that the experiments were mainly separated into low and high turbulence cases
A grille was placed at the upstream of the airfoil test section which results in different aerodynamic characteristics of flow over the airfoil with and without section which results in different aerodynamic characteristics of flow over the airfoil with and a Gurney without flap
Summary
Wind power generation technology has been maturely developed in the past decades. Airfoil is a basic element of a wind turbine blade, and its aerodynamic characteristics have a major influence on the wind energy conversion efficiency. Among the conventional rotor aerodynamic design strategy, the blade add-ons were of particular interest to further improve wind energy efficiency. Mounting flap to the airfoil trailing edge was one of the most feasible methods to improve the aerodynamic performance of wind turbines. In addition to power production, such a technique can effectively reduce the aerodynamic loads both of wind turbine blades and tower. If a sophisticated controller was implemented, the flap can further reduce turbulence-induced fatigue loads, so that longer lifetime was guaranteed.
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