Dynamic Analysis of a Wind Turbine Gearbox Towards Prediction of Mechanical Tonalities

Abstract

This dissertation describes the development of a methodology and modelling approach to lower the mechanical noise of the drive train of a modern wind turbine with a strong focus on the wind turbine gearbox. Although this mechanical noise is not the main noise source from a wind turbine, it could - especially when it contains audible tonal components - result in non-conformity to local noise regulations. This becomes more stringent when wind turbines are installed closer to urbanised areas. This research is motivated by inefficiencies in a cost and time consuming reactive trial and error approach to reduce or remove audible mechanical tonalities from the wind turbine noise. This dissertation focusses on the mechanical tonalities linked with the wind turbine gearbox. This mechanical noise originates from the interaction between the gears inside the gearbox, and then propagates directly airborne through the air or indirectly structure-born through the other wind turbine components to the outside. Two fundamental approaches exist to reduce or to remove a mechanical tonality. The first approach attempts to reduce the noise source by optimising the gears for low-noise. The second approach modifies the propagation path, also called transfer path from the source to the listener, such that the noise originating from the noise source is not amplified or even attenuated when it reaches the listener. The methodology proposed in this dissertation focusses on the second approach: using virtual prototyping models to assess and to optimise these transfer paths. The development of this methodology consists of 3 main parts: firstly individual components of the wind turbine gearbox are investigated in detail and if necessary experimentally validated. Secondly these individual components are assembled into a wind turbine gearbox model. The impact of these individual components on the global eigenmodes of the gearbox are investigated, and the model of the complete gearbox is experimentally validated by performing an experimental modal analysis. Lastly a model of two gearboxes on the end-of-line test rig is generated, investigated and also experimentally validated. This step-by-step approach, including the numerous experimental validation cases, resulted in a significant increase in both insight and confidence in the dynamic behaviour predicted by these virtual prototyping models. This dissertation demonstrates this methodology and modelling approach by performing two optimisation cases. The first optimisation case focusses on the impact of the bearings on the resulting vibrations. The second optimisation case modifies the flexible gearbox housing, which is considered the most dominant component, to shift an important eigenmode out of the operating range of the wind turbine. Both these optimisation cases clearly illustrate the potential of pro-actively using virtual simulation models to optimise the noise and vibration behaviour of the wind turbine gearbox during its design.Abstract Acronyms Contents List of Figures List of Tables 1 Introduction 1.1 Research objectives 1.2 Scope definition 1.3 Research facilitators 1.4 Research strategy 1.4.1 Modelling 1.4.2 Experimental validation 1.4.3 Used software 1.5 Main contributions 1.6 Overview of the dissertation 2 Introduction to wind turbines and wind turbine noise 2.1 Introduction 2.2 Climate change and renewable energy 2.3 Wind turbines 2.3.1 Layout 2.3.2 Operating range 2.4 Wind turbine noise 2.4.1 Wind turbine noise characteristics 2.4.2 Wind turbine noise sources 2.4.3 Wind turbine noise perception and annoyance 2.4.4 Regulations on wind turbine noise 2.5 Wind turbine farm planning 2.5.1 Site location 2.5.2 Site layout 2.6 Wind turbine gearboxes 2.6.1 Design 2.6.2 Excitation sources 2.7 Wind turbine noise transfer paths 2.8 Conclusions 3 Wind turbine drive train modelling, an overview 3.1 Wind turbine drive train design load models 3.2 Noise and vibration models 3.2.1 Non wind turbine gearboxes 3.2.2 Wind turbine drive train noise and vibration modelling 3.3 Limitations and shortcomings of current models to predict the NV behaviour 4 Modelling and experimental validation of individual wind turbine gearbox components 4.1 Introduction 4.1.1 Multibody modelling 4.2 Gearbox housing 4.2.1 Individual components 4.2.2 Assembly of individual components 4.2.3 Usage in MB model 4.3 Planet carriers 4.3.1 Modelling 4.3.2 Experimental validation 4.3.3 Conclusions 4.4 Bearings 4.4.1 Bearing stiffness determination 4.4.2 Bearing force introduction 4.5 Shafts and gears 4.5.1 Shafts 4.5.2 Gears 4.6 Conclusions 5 Modelling and experimental validation of a wind turbine gearbox 5.1 Introduction 5.2 HSH and MC 5.2.1 Model 5.2.2 Measurements 5.2.3 Correlation 5.2.4 Conclusions 5.3 Full gearbox - Structural model 5.3.1 Model 5.3.2 Measurements 5.3.3 Correlation 5.3.4 Conclusions 5.4 Full gearbox - Acoustic model 5.4.1 Need for acoustic modelling 5.4.2 Acoustic model 5.4.3 Structural - acoustic linking 5.4.4 Acoustic runup simulation 5.5 Conclusions 6 Modelling and experimental validation of two wind turbine gearboxes on the end of line test rig 6.1 Modelling 6.1.1 Impact of the flexible supporting structure on the global dynamics 6.1.2 Impact of load on the global dynamics 6.1.3 Sensitivity study 6.2 Measurements 6.3 Correlation 6.4 Conclusions 7 Virtual prototyping methodology to pro-actively avoid tonal wind turbine noise 7.1 Modelling method 7.1.1 Mechanical noise sources 7.1.2 Mechanical transfer paths 7.1.3 Acoustic radiation 7.2 Required analysis 7.3 Conclusions 8 Optimisation cases 8.1 Optimisation case 1: Impact of bearings on the resulting wind turbine gearbox vibration amplitudes 8.1.1 Using transfer path analysis to gain insight in the transmission of gear excitation through the different bearing positions 8.1.2 Effect of bearing stiffness & damping values on the transmission of gear excitation 8.1.3 Effect of bearing position on the transmission of gear excitation 8.1.4 Conclusions 8.2 Optimisation case 2: Wind turbine gearbox housing bending modes 8.2.1 Conclusions 8.3 Conclusions 9 Conclusions 9.1 Overview and main contributions 9.2 Recommendations for future research 9.2.1 Sources 9.2.2 Transfer paths 9.2.3 Noise radiation A Femtools A.1 Simpack model reader A.2 Simpack model writer A.3 Simpack solver & results reader B Roller based bearing model B.1 Distance calculation B.2 Roller force calculation C Overview on experimental validation campaigns C.1 Individual wind turbine gearbox components C.1.1 Torque arm C.1.2 Low speed ring wheel C.1.3 Intermediate bearing housing, low speed side C.1.4 High speed housing and main cover C.1.5 Assembled gearbox housing C.2 Assembled gearbox C.2.1 High speed housing and main cover C.2.2 Complete gearbox Bibliography List of publicationsnrpages: 266status: publishe