Along-Wind Aerodynamic Damping of Wind Turbine Towers: Determination by Wind Tunnel Tests and Impact on Tower Lifetime

Robert Fontecha,Frank Kemper,Stefan Witter,Markus Feldmann,Ralf Schelenz

doi:10.3390/en15061984

Abstract

As wind turbines become larger and their towers more slender, aeroelastic effects play a bigger role in the wind turbine’s dynamic behavior. This study focuses on the along-wind aerodynamic damping of wind turbine towers, which has been determined by wind tunnel experiments using the forced oscillation method according to Steckley’s approach. Reynolds number scale effects have been considered through surface roughness modifications using sand paper and a dimple pattern, which have been described in detail. The wind tunnel measurements are performed in sub-critical, critical and trans-critical flow regimes, as well as in low- and high-turbulence conditions, which allows for an accurate description of the required relative roughness and Reynolds numbers for achieving trans-critical conditions. The resulting along-wind aerodynamic damping values according to Steckley’s and Holmes’ approaches are compared, and an analytical relation between them is established. Both approaches are then used in aeroelastic multi-body-simulations of an onshore 6 MW reference wind turbine and their impact on the wind turbine lifetime is evaluated through fatigue proofs at the tower base section. Holmes’ approach seems more appropriate for the application in aeroelastic multi-body simulations. A lifetime extension for the wind turbine tower of approximately 0.4% is achieved for the reference wind turbine tower, which roughly corresponds to 1 to 2 months for 20 years of operation. An analytical expression is given for the estimation of the tower’s aerodynamic damping in parked and operating conditions.

Highlights

IntroductionWind energy is still one of the main contributors to the global transition to renewable energies
In the last few years, the number of studies about the aerodynamic damping of wind turbines has increased. These studies mainly focus on the aerodynamic damping of the wind turbine rotor oscillating in wind direction due to the first bending mode shape of the wind turbine tower, which can reach damping rations between 5% and 15% depending on rotor dimension and other parameters [2–5]
While the aerodynamic damping of the rotor is already considered in state-of-the art aeroelastic software for wind turbines [3,4,11], the mentioned studies aim at its determination from real wind turbines or to its characterization and identification of its most relevant parameters

Summary

Introduction

Wind energy is still one of the main contributors to the global transition to renewable energies. To achieve the objective of remaining below a 2 ◦ C global temperature increase, the percentage of wind energy should be increased to over 30% by 2050 [1]. This requires an increase in the annually wind energy installation and ideally cheaper and more efficient wind turbines. This has been classically achieved through higher wind turbines with larger rotors. In the last few years, the number of studies about the aerodynamic damping of wind turbines has increased. While the aerodynamic damping of the rotor is already considered in state-of-the art aeroelastic software for wind turbines [3,4,11], the mentioned studies aim at its determination from real wind turbines or to its characterization and identification of its most relevant parameters

Objectives

Results

Conclusion