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2014 | Buch

Smart Rotor Modeling

Aero-Servo-Elastic Modeling of a Smart Rotor with Adaptive Trailing Edge Flaps

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A smart rotor is a wind turbine rotor that, through a combination of sensors, control units and actuators actively reduces the variation of the aerodynamic loads it has to withstand. Smart rotors feature promising load alleviation potential and might provide the technological breakthrough required by the next generation of large wind turbine rotors.

The book presents the aero-servo-elastic model of a smart rotor with Adaptive Trailing Edge Flaps for active load alleviation and provides an insight on the rotor aerodynamic, structural and control modeling. A novel model for the unsteady aerodynamics of an air foil section with flap is presented and coupled with a multi-body structural representation. A smart rotor configuration is proposed, where the Adaptive Trailing Edge Flaps extend along the outer 20 % of the blade span. Linear Quadratic and Model Predictive algorithms are formulated to control the flap deflection. The potential of the smart rotor is finally confirmed by simulations in a turbulent wind field. A significant reduction of the fatigue loads on the blades is reported: the flaps, which cover no more than 1.5 % of the blade surface, reduce the fatigue load by 15 %; a combination of flap and individual pitch control allows for fatigue reductions up to 30 %.

Inhaltsverzeichnis

Frontmatter
Introduction
Abstract
During the past 25 years, the size of utility scale horizontal axis wind turbines grew uninterrupted, constantly seeking a reduction of the cost of energy, figure 1.1. As the rotor size increases, all wind turbine components, and the blades in particular, have to withstand higher loads. In the past, the higher structural requirements were mainly satisfied by up-scaling the load carrying components and thus increasing the weight of the structure, or by employing compounds with an higher specific strength - and cost. Sieros et al.
Leonardo Bergami
Simulation Environment
Abstract
A substantial part of the analysis presented in this book is based on simulations of the aero-servo-elastic response of the wind turbine model chosen as reference. The simulations are performed with DTU Wind Energy’s aeroelastic code HAWC2 [56]. The chapter briefly outlines the main characteristics of the aeroelastic code, and introduces the NREL 5 MW wind turbine, which will be used as reference model, first in its baseline configuration, and thereafter in a smart rotor configuration featuring adaptive trailing edge flaps.
Leonardo Bergami
Load Analysis
Abstract
A first series of aeroelastic simulations is performed on the NREL 5 MW turbine in its baseline configuration [51]. The objective is to identify the operational conditions that give rise to loads that are critical for the turbine design. In fact, active load alleviation in such conditions would be particularly beneficial, as it would allow for lower structural design requirements.
Leonardo Bergami
ATEFlap Aerodynamic Model
Abstract
The load analysis has highlighted the importance of an aerodynamic model able to describe not only the steady (or quasi-steady) effects of airfoil motion and flap deflection, but also the unsteady dynamics of the forces and moments, both in attached and stalled flow conditions. The model should also have low computational requirements to allow for an efficient integration with the BEM-based simulation environment of the aeroelastic code HAWC2, section 2.1.
Leonardo Bergami
Adaptive Trailing Edge Flap Placement
Abstract
The chapter proposes a smart rotor configuration for the NREL 5 MW turbine with Adaptive Trailing Edge Flaps (ATEF) on each of the blades. Flaps with the aerodynamic proprieties presented in the previous chapter are included in the HAWC2 model of the wind turbine, and aeroelastic simulations are performed to determine the blade root flapwise bending moment response to step deflections of flaps located at different positions along the blade span. The response characteristics guide the choice on placement and extension of the flap actuators, thus defining the smart rotor configuration that will be used in all the following active load alleviation analysis. A brief comparison of the blade root load variation achieved by the proposed actuator configuration, and the bending moment variations observed on the turbine rotor during normal operation concludes the chapter.
Leonardo Bergami
Preliminary Evaluation with Feed-Forward Cyclic Control
Abstract
Preliminary investigations to determine the smart rotor potential are carried out with a simplified feed-forward control approach: flap deflections and blade pitch angles follow pre-determined cyclic trajectories; the control signals are only function of the blade azimuthal position, and are repeated identically at each rotor revolution. The cyclic trajectories are determined offline by solving a constraint optimization problem that directly targets the control objectives: blade root flapwise bending moment variation, and aerodynamic power output.
Leonardo Bergami
Model Based Control Algorithms for a Rotor with ATEF
Abstract
The chapter presents two control algorithms that aim at actively alleviating the load variations on the turbine structure using the ATEF smart rotor configuration presented earlier. The control algorithms include feedback from measurements of the actual turbine structural deformations, and are thus able to address load variations of both periodic and stochastic nature, overcoming the limitations of the feed-forward cyclic control presented in the previous chapter.
Leonardo Bergami
Summary of Findings and Future Work
Abstract
The chapter briefly recalls the steps undertaken in the development of the smart rotor aero-servo-elastic model, and the analysis of the smart rotor configuration performance. First, the main findings from the previous chapters are summarized, accompanied by suggestions for future research work. A brief discussion on the estimation of the cost of energy with a smart rotor configuration follows; the chapter is concluded by few indications on desirable characteristics for an Adaptive Trailing Edge Flap actuator.
Leonardo Bergami
Conclusion
Abstract
The study presented the development of a smart rotor configuration with Adaptive Trailing Edge Flaps (ATEF) for active load alleviation. The smart rotor performance is evaluated by means of simulations with the aero-servoelastic code HAWC2, reproducing the wind field conditions specified by the IEC standard. The ATEFlap aerodynamic model is implemented in the simulation code to account for the steady and dynamic effects of the flap deflection on the aerodynamic forces and pitching moment of 2D airfoil sections; a good agreement between the model and computational fluid dynamic simulations is reported both in attached and separated flow conditions.
Leonardo Bergami
Backmatter
Metadaten
Titel
Smart Rotor Modeling
verfasst von
Leonardo Bergami
Copyright-Jahr
2014
Electronic ISBN
978-3-319-07365-1
Print ISBN
978-3-319-07364-4
DOI
https://doi.org/10.1007/978-3-319-07365-1