On the Determination of the Aerodynamic Damping of Wind Turbines Using the Forced Oscillations Method in Wind Tunnel Experiments

Robert Fontecha,Markus Feldmann,Frank Kemper

doi:10.3390/en12122452

Abstract

The development of wind turbine technology has led to higher and larger wind turbines with a higher sensitivity to dynamic effects. One of these effects is the aerodynamic damping, which introduces favorable damping forces in oscillating wind turbines. These forces play an important role in the turbine lifetime, but have not yet been studied systematically in detail. Consequently, this paper studies the plausibility of determining the aerodynamic damping of wind turbines systematically through wind tunnel experiments using the forced oscillation method. To this end, a 1:150 scale model of a prototype wind turbine has been fabricated considering Reynolds number effects on the blades through XFOIL calculations and wind tunnel measurements of airfoil 2D-section models. The resulting tower and wind turbine models have been tested for different operation states. The tower results are approximate and show low aerodynamic damping forces that can be neglected on the safe side. The measured aerodynamic damping forces of the operating turbine are compared to existing analytic approaches and to OpenFAST simulations. The measured values, although generally larger, show good agreement with the calculated ones. It is concluded that wind tunnel forced oscillations experiments could lead to a better characterization of the aerodynamic damping of wind turbines.

Highlights

Wind energy has become in recent decades one of the main renewable power generating capacities to reduce the emissions of CO2
The study presented in this paper aims to change this by proving the plausibility of determining the aerodynamic damping of wind turbines in wind tunnel measurements through forced oscillations tests
The results express increasing aerodynamic damping with increasing reduced speed as well as an increase of the system stiffness and natural frequency

Summary

Introduction

Wind energy has become in recent decades one of the main renewable power generating capacities to reduce the emissions of CO2. Wind energy was the second largest power generating capacity in the EU in 2016 with 16.7% of the total generated power [1]. This is partly due to the rapid development of wind turbine technology and multi-megawatt horizontal axis wind turbines (HAWT), which has led to higher hub heights and larger rotor diameters [2]. As towers get higher, more slender and more flexible, dynamic and aerodynamic aspects play increasingly a decisive role in the wind turbine behavior and their design. One of these aerodynamic aspects is the aerodynamic damping. If high oscillation amplitudes occur, like in the case of tall onshore wind turbines and offshore wind turbines with monopile foundations, the contribution of the aerodynamic damping to the total damping is significant and beneficial, as the total damping is usually increased

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