The phenomenon of wake meandering is long known empirically, but has so far not been treated in a satisfactory manner on the wind turbine load modelling side. We present a consistent, physically based theory for wake meandering, which we consider of crucial importance for the overall description of wind turbine loadings in wind farms. In its present version, the model is confined to single wake situations-including a simple heuristic description of wake interaction with a reflecting surface. Contrary to previous attempts to model wind turbine wake loading, the present approach opens for a unifying description in the sense that turbine power and load aspects can be treated simultaneously. This capability is a direct and attractive consequence of the model being based on the underlying physical process, and it potentially opens for optimization of wind farm topology, wind farm operation, as well as control strategies for the individual turbine.The application of the proposed dynamic wake meandering methodology with existing aeroelastic codes is straightforward and does not involve any code modifications. The strategy is simply to embed the combined effect of atmospheric turbulence, added wake turbulence and the intermittent 'turbulence contribution', caused by wake meandering, in files replacing the traditional turbulence file input to aeroelastic computations. Copyright wake profi le is typically assumed Gaussian, 4 and the centreline defi cit decays monotonically with a rate strongly dependent on the ambient turbulence, but also on the turbulence generated by the velocity defi cit profi le itself and the turbulence generated by the mechanical mixing process in the rotor plane. The development of the far wake was modelled with an eddy viscosity model by Ainslie 4 taking into account the ambient turbulence as well as the defi cit-shear-generated turbulence.The problems and uncertainties, by comparing model results with full-scale measurements, were noticed by Taylor et al., 5 based on an investigation where model results were compared with wake measurements on the Nibe 630 kW turbines. He describes that the variations in on-site wind direction shift the wake across the downstream rotor disc, and this will increase the average power output from the downstream turbine measured over some time-a mechanism not taken into account in the modelling. Ainslie 6 discusses the subject in more detail and mentions that wake meandering effects can have considerable infl uence on measured wake defi cits, in particular under non-stable atmospheric conditions. It seems that Ainslie 6 is the fi rst to model the effect from wake meandering on wake defi cits by correlating the wake meandering to the variability in the wind direction. In this way, he computes the averaging of wake defi cits for two full-scale experiments, and the infl uence from the meandering is signifi cant in reducing the depth of the defi cits. 6 Further comparisons of model and experimental results, including the correction for meandering for a number of different ...
The theory and results of two experimental methods for estimating the modal damping of a wind turbine during operation are presented. Estimations of the aeroelastic damping of the operational turbine modes (including the effects of the aerodynamic forces) give a quantitative view of the stability characteristics of the turbine. In the first method the estimation of modal damping is based on the assumption that a turbine mode can be excited by a harmonic force at its natural frequency, whereby the decaying response after the end of excitation gives an estimate of the damping. Simulations and experiments show that turbine vibrations related to the first two tower bending modes can be excited by blade pitch and generator torque variations. However, the excited turbine vibrations are not pure modal vibrations and the estimated damping is therefore not the actual modal damping. The second method is based on stochastic subspace identification, where a linear model of the turbine is estimated alone from measured response signals by assuming that the ambient excitation from turbulence is random in time and space. Although the assumption is not satisfied, this operational modal analysis method can handle the deterministic excitation, and the modal frequencies and damping of the first tower and first edgewise whirling modes are extracted. Copyright © 2006 John Wiley & Sons, Ltd.
A new load-reducing control strategy for individual blade control of large pitch-controlled wind turbines is presented. This control concept is based on local blade inflow measurements and offers the possibility of larger load reductions, without loss of power production, than seen in other state-of-the-art load-reducing concepts. Since the new flow-based concept deviates significantly from previous published load-reducing strategies, a comparison of the performance based on aeroelastic simulations is included. Advantages and drawbacks of the systems are discussed.
Violent edgewise blade vibrations have in recent years been a large problem for some stall-regulated wind turbines. Owing to the complexity of the phenomenon, it has been difficult to predict the risk of these vibrations with aeroelastic load prediction tools. One problem is the choice of parameters in the aeroelastic model, e.g. structural damping and aerodynamic aerofoil characteristics. In many cases a high degree of uncertainty in the predicted response exists and the need for experimental verification methods is obvious. In this work a new method to identify the effective damping for the edgewise blade mode shape for wind turbines has been developed. The method consists of an exciter mechanism which makes it possible to excite the edgewise blade mode shapes from the wind turbine nacelle. Furthermore, the method consists of an analysis method which enables a straightforward determination of the damping. The analysis method is based on a local blade whirl description of the edgewise blade vibrations. The method is verified on a Bonus wind turbine, and for this specific turbine the effective damping for edgewise blade vibrations has been determined. The results support the further development of aeroelastic models and show potential for fine-tuning of parameters of importance for the edgewise blade vibration problem. Furthermore, the method can be used for experimental investigation of the risk of edgewise blade vibrations for a specific turbine.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.