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

Junwei Yang,Nailu Li,Hua Yang,Xiangjun Wang

doi:10.3390/jmse10030371

Abstract

The present work aimed to investigate the aerodynamic characteristics of a pitching wind turbine airfoil with a Gurney flap under turbulent inflow. Experiments were carried out for the DTU-LN221 offshore wind turbine airfoil under different turbulence levels at Reynolds number 105 order of magnitude by replacing the grilles in the wind tunnel. The dynamic stall characteristics were analyzed by measuring surface pressure and near-wake flow field. The pressure results demonstrated that with the increase of turbulence intensity, the differences in lift hysteresis loops between baseline airfoil and flapped airfoil became smaller. With the turbulence intensity from 0.5% to 10.18%, the maximum lift increment of the Gurney flap decreased from 14.32% to 4.34% (i.e., 0–20° pitching oscillation). In a more extensive range of oscillation, the capability for the lift-improvement dropped down a bit more (i.e., 0–25°). A brief aerodynamic damping analysis indicated that the Gurney flap was more stable in turbulent conditions than the baseline airfoil. Besides, hysteresis loops of the wake were analyzed to compare the difference between the flapped airfoil and the baseline airfoil. Unlike the studies of static airfoils, the results may help better understand the dynamic characteristics of offshore wind turbines with Gurney flaps for practical situations.

Highlights

In the face of the Paris agreement being finalized, all contracting countries need to contribute to dealing with global climate change
It is found that the power spectral density (PSD) of the frequency of the vortices that mainly generate energy was below 40 Hz
Compared with the uniform inflow, the Gurney flap leads to an additional increase in lift and pitching moment under turbulent conditions

Summary

Introduction

In the face of the Paris agreement being finalized, all contracting countries need to contribute to dealing with global climate change. The measurement results proved the efficiency of Gurney flaps, with the power of the full-size wind turbine increasing by 4.3% in a month. Another example was the DTU-10 MW wind turbine designed by Bak et al [10]. The method of improving aerodynamic performance was put forward by adding Gurney flaps with a chord length height of 1% to 3%, and the designed results were verified by software EllipSys3D . Ebrahimi and Movahhedi [11] numerically investigated the flow behavior and the output power caused by the Gurney flap based on the NREL Phase VI wind turbine. The Vestas® (global largest wind power manufacturer) optimization service, for example, claims that Gurney flaps increase the annual energy production of a wind turbine by 1.2% per year [14]

Methods

Results

Conclusion