Aeroelastic measurements and simulations of a small wind turbine operating in the built environment

S.P Evans,D.R Bradney,P.D Clausen

doi:10.1088/1742-6596/753/4/042013

Abstract

Small wind turbines, when compared to large commercial scale wind turbines, often lag behind with respect to research investment, technological development, and experimental verification of design standards. In this study we assess the simplified load equations outlined in IEC 61400.2-2013 for use in determining fatigue loading of small wind turbine blades. We compare these calculated loads to fatigue damage cycles from both measured in-service operation, and aeroelastic modelling of a small 5 kW Aerogenesis wind turbine. Damage cycle ranges and corresponding stress ratios show good agreement when comparing both aeroelastic simulations and operational measurements. Loads calculated from simplified load equations were shown to significantly overpredict load ranges while underpredicting the occurrence of damage cycles per minute of operation by 89%. Due to the difficulty in measuring and acquiring operational loading, we recommend the use of aeroelastic modelling as a method of mitigating the over-conservative simplified load equation for fatigue loading.

Highlights

Small wind turbines are defined by IEC 61400.2-2013 as having a swept area less than 200 m2 which corresponds to a blade diameter and power output less than 16 m and 50 kW respectively [1]
In this study we compare the simple load model specified in the standard for fatigue life formulation with both aeroelastic simulations and in-service load measurements
Rainflow counted and ranked damage cycles produced via aeroelastic simulations show very good agreement with field measurements acquired in similar inlet wind conditions

Summary

Introduction

Small wind turbines are defined by IEC 61400.2-2013 as having a swept area less than 200 m2 which corresponds to a blade diameter and power output less than 16 m and 50 kW respectively [1]. Small wind turbines have several significant operational differences compared to large wind turbines used for commercial scale generation, including, but not limited to; higher operational rotational speeds and tip speed ratios, the influence of low Reynolds number and high angle of attack aerodynamics (especially during rotor start-up), passive yaw control (typically achieved via a tail fin) which can result in high gyroscopic loads, and potential for siting within the built environment resulting in highly turbulent inlet flow and unsteady aerodynamics [2, 3, 4, 5] These factors can lead to comparatively complex operational dynamics and service loading, which can be detrimental to fatigue critical components such as blades and drive shafts [6, 7, 8, 9].

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