Abstract
In this work, a novel rotor rebalancing algorithm is tested in a simulation environment to evaluate its performance when facing both aerodynamic and inertial imbalances. The algorithm, ...starting from a generic measurement collected on the wind turbine fixed frame, is capable of remotely minimizing once per revolution vibrations, avoiding the need for on-site inspections, and without requiring detailed information about the machine. Indeed, once access to the pitch system is granted, this algorithm simply iteratively computes the pitch angle that needs to be applied to each individual blade in order to rebalance the rotor.
Several turbulent time histories, with changing mean inflows, were simulated with the goal of testing the proposed method in realistic field conditions. Overall, the algorithm proved capable of significantly reducing the desired once per revolution vibrations in 3 to 4 iterations, irrespective of the imbalance root cause, its severity and its location. The method also appeared quite robust, showing that the found rebalanced configurations guarantee reduced vibrations no matter the machine operating point.
In this work, the wind sensing technology that exploits the turbine rotor as an anemometer is further developed into a non-deterministic formulation. First, an inflow-turbine response map is ...identified, which relates out and in-plane blade root bending moments to both vertical and horizontal shears and misalignments. Then, this linear model is used with and without a Kalman filter to estimate online the wind field at the rotor disk once blade loads are measured. A comprehensive simulation study, including different wind speeds and turbulence intensity levels, was performed to evaluate the accuracy of the new non-deterministic formulation. The results show that introducing a Kalman filter in the estimation process allows for a significant improvement in the angle estimates with respect to the deterministic formulation, with no considerable additional computational cost.
Abstract
This study explores the effect of different technology choices on the life cycle Greenhouse Gases (GHG) emissions of wind turbines. It aims at identifying possible improvement pathways and ...quantifying potential benefits. First, an automated Life Cycle Assessment (LCA) model is developed and validated against other studies. The breakdown of the resulting Impact Of Energy (IOE) by life stages, components and materials is presented for a selected reference turbine. Sensitivity analyses are conducted on the different hypotheses to model the turbine life cycle. The model is then applied to analyze the potential effect of turbine size, foundation type, tower type, drivetrain technology, carbon-fiber blades and thermoplastic polymer resin for the blades. The tower type (especially wooden tower) and the thermoplastics (allowing to recover materials at the end-of-life) are identified to have the biggest potential to reduce the life cycle environmental impact of wind energy.
Abstract Noise remains an obstacle to the advancement of onshore wind energy. Despite the ongoing debate on the effects of infrasound on human health, especially from wind turbines, there is ...consensus that the blade passing frequency (BPF) in the infrasound range modulates the audible higher-frequency sound and creates a rhythmic “swishing” sound at farther distances. This paper presents a simulation framework for assessing infrasound noise (<20 Hz) from wind turbines, which was designed to capture the relevant physics without incurring in overwhelming computational costs. The flow is modelled using large eddy simulation (LES) and is coupled through an actuator line method (ALM) to the aeroelastic model of a wind turbine. The use of an ALM significantly reduces the computation effort compared to blade-resolved CFD approaches. Moreover, the Ffowcs Williams-Hawkings (FW-H) acoustic analogy is applied on a permeable integration surface that surrounds the entire wind turbine, thereby capturing the coupled effects of rotor, tower, and the near-wake turbulence shed by the turbine. The present approach is shown to be capable of resolving rotor-tower interactions as tonal peaks at BPF and its harmonics, enabling the evaluation of design and control measures to mitigate infrasound noise emissions from wind turbines.
Abstract In this work, a load-based yaw misalignment observer was tested and validated with turbine and mast data collected during a wake steering and characterization campaign. A shallow ...feed-forward neural network was used to map the relation between the yaw misalignment and the in-and out-of-plane blade load harmonics for a 3.5 MW machine, and its performance was analysed over about 108 full days of useful data. Confirming previous findings, this simple neural network was able to accurately estimate the yaw misalignment, with an average 10-minute absolute error of at most 4°. The performance of the yaw misalignment observer was compared to the one of the standard onboard wind vane during the wake steering campaign. Results indicate that the wind vane may significantly overestimate the misalignment for large angles, possibly on account of the wake rotation and flow distortion effects caused by the nacelle. The observer on the other hand, sampling the flow at the rotor disk and not behind it, is not affected by such phenomena and could therefore provide a more accurate measurement of the misalignment angle, possibly improving the performance of wake steering. When the turbine is already equipped with load sensors, this is obtained without the need to install and maintain extra hardware, which instead is the case with spinner-mounted anemometers or lidars.
This work reports preliminary findings on the field validation of the "rotor as a sensor" concept. In a nutshell, the idea is to use the rotor response in order to measure the wind inflow, ...effectively turning the whole rotor into a sort of generalized anemometer capable of estimating wind speed, shears and directions. In turn, these quantities can be used for optimizing turbine and farm-level performance. Here a purely data-driven method is used, where a wind observer is first identified using flow field measurements (obtained by a met-mast) together with the corresponding blade root load harmonics. Once the observer has been identified, the wind inflow is estimated online during turbine operation by feeding it with measured blade root harmonics. Preliminary results reported herein seem to be very encouraging.
This study explores the potential benefits of considering Lidar-assisted control (LAC) at the first stages of wind turbine design. The proposed methodology starts with a load analysis of several ...reference wind turbines to understand which design constraints can be influenced by the use of LAC. The blade and tower of each analyzed model are redesigned considering LAC-induced reductions in key driving quantities. Preliminary results suggest modest reductions in LCOE with potentially significant benefits limited to the tower. The study also discusses the requirements on LAC system purchase and O&M costs, for both onshore and offshore machines, to achieve a reduction in LCOE.
This paper presents a new way of detecting imbalances on wind turbine rotors, by using a harmonic analysis of the rotor response in the fixed frame. The method is capable of distinguishing among ...different root causes of the imbalance. In addition, the imbalance severity and location, i.e. the affected blade, can be identified. The automatic classification of the imbalance problem is obtained by using a neural network. The performance of the method is illustrated with the help of different fault scenarios, within a high-fidelity simulation environment.
We use the capabilities of a multi-disciplinary design tool to provide a definition of a 20 MW wind turbine. Starting from an aero-elastic model obtained through a classic scaling procedure, we ...conduct an aero-structural optimization of the rotor through a staged redesign process, in which we optimize primary characteristics of the rotor including the blade shape, the solidity and a certain amount of native structural tailoring. The process is based on a series of parametric analysis, in order to assess the impact of a variation of macro design parameters on the fundamental performance of the turbine. The redesign activity shows remarkable advantages in terms of blade mass reduction and load alleviation, highlighting directions for the development and optimization of very large rotors.
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