To address the acoustic behaviour of wind turbines, particularly tonalities, in an early design stage, accurate simulation toolchains have to be developed. In this work a novel simulation approach for the prediction of tonalities of direct drive wind turbines is presented. Comprehensive work is carried out in the fields of electromagnetic force excitation, structural sound transfer and radiation as well as airborne sound propagation. The developed methods are combined to a simulation toolchain to formulate a multi-physical system model of a direct drive wind turbine in order to predict tonal sound behaviour. These methods will be presented and discussed in detail in the course of this work. First, the approach, integrating the electromagnetic airgap forces of the large generator into a multi body simulation model of the mechanical turbine, is explained and validated with test bench measurements. Following, the modeling of the respective mbs is presented which calculates the resulting surface velocities. This model is solved in the time domain to account for the interaction between the external loads that are highly nonlinear and low-frequency and the high-frequency excitation forces of the generator. Subsequently, the methods for calculating the airborne sound emission in the vincinity of the turbine resulting from the surface velocities are discussed.

The usage of journal bearings as planetary bearings in wind turbines instead of roller bearings has become more common in recent years. Their usage is advantageous, due to smaller installation space needed compared to roller bearings allowing for higher power densities of wind turbine drive trains. However, this technology presents a challenge since there is currently no standardized approach for the design of planetary journal bearings regarding wear. Due to varying wind speeds and dynamic operating events a large variation of loads has to be considered in the design process of a planetary journal bearing for wind turbines. Some of these loads are considered potentially critical to the journal bearing in terms of wear. Identifying these critical load areas early in the design phase supports a reliable bearing design and wind turbine operation.This paper introduces a method to identify critical operating conditions for planetary journal bearings using a simulation tool chain, which couples a multi body simulation (MBS) model of a wind turbine with an elasto-hydrodynamic (EHD) model of the planetary journal bearing. Based on the EHD results critical operating conditions are determined for the planetary bearing. Furthermore, methods are implemented to reduce the number of required EHD simulations for analysing the bearing design. The combination of the identification of critical operating conditions, while reducing the computational effort leads to a simulation methodology, which enables a faster bearing design assessment considering the wide variation of wind turbine operating conditions. The applicability of this method is demonstrated by a simplified use case.Firstly, this paper introduces the MBS model and the parameter space that describes possible combinations of bearing loads such as forces, moments and rotational speed. Due to the number of combinations and the EHD computing effort, the identified parameter space is secondly sampled statistically to reduce the simulation effort. A risk map is derived from the EHD results, to easily indicate potentially critical operating conditions for the planetary journal bearing.

In this paper the methodology and results of the validation of a multi-physical system model of a direct drive wind turbine are presented. The analyzed model serves the purpose of examining the structure borne sound resulting from electromagnetic excitations inside the turbine’s generator. To study the accuracy of this model and to increase the confidence in the simulation results, an experimental validation is performed in the course of this work. Hereby, the simulation results are compared with data from a measurement campaign in which the real generator was tested on a full-scale system test bench. The validation takes the structure-borne sound transfer, modal behavior of the generator and effects of structural dynamics into account.

Decreasing the levelized cost of energy is a major design objective for wind turbines. Accordingly, the control is generally optimized to achieve a high energy production and a high-power coefficient. In partial load range, speed and torque are controlled via the generator torque but the rotor torque determines the power coefficient of the turbine. High uncertainties for the uncalibrated low-speed shaft torque measurement and varying drivetrain efficiencies which depend on the speed, load and temperature lead to a torque control error that reduces the power coefficient of the wind turbine. In this paper the rotor torque control error and the impact on the power coefficient of wind turbines is quantified. For this purpose, the variation of drivetrain efficiency is analyzed. An efficiency model for the wind turbine drivetrain is build and validated on the test bench. Then, the influence of the drivetrain speed, torque loads, non-torque loads, and temperature on the efficiency is quantified. Finally, the influence of the rotor torque control error on the power coefficient was simulated with an aerodynamic model. The results show that of all examined influences only torque and temperature significantly impacting the efficiency leading to rotor torque control errors that reduce the power coefficient and consequently increase the levelized cost of energy. Improved efficiency measurement on WT test benches or drivetrain efficiency modelling can reduce the rotor torque control error and therefore decrease the LCOE.