Servo-aeroelastic tailoring of wind turbines using new active-to-passive control systems

Lead Research Organisation: University of Bristol
Department Name: Aerospace Engineering

Abstract

In recent years, the cost of energy produced by renewable supplies has steadily decreased. This factor, together with socio-economical reasons, has made renewable energies increasingly competitive, as confirmed by industry growth figures. Considering wind turbines (WTs), there are some interesting technical challenges associated with the drive to build larger, more durable rotors that produce more energy, in a cheaper, more cost efficient way. The rationale for moving towards larger rotors is that, with current designs, the power generated by WTs is theoretically proportional to the square of the blade length. Furthermore, taller WTs operate at higher altitudes and, on average, at greater wind speeds. Hence, in general, a single rotor can produce more energy than two rotors with half the area. However, larger blades are heavier, more expensive and increasingly prone to greater aerodynamic and inertial forces. In fact, it has been shown that they exhibit a cubic relationship between length and mass, meaning that material costs, inertial and self-weight effects grow faster than the energy output as the blade size increases. In addition, larger blades also have knock-on implications for the design of nacelle components.

The wind-field through which the rotor sweeps varies both in time and space. Consequently, the force and torque distributions for the blades exhibit strong peaks at frequencies which are integer multiples of the rotor speed. Additional peaks are induced by lightly damped structural modes. The loads on the blades combine to produce unbalanced loads on the rotor which are transmitted to the hub, main bearing and other drive-train components. These unbalanced loads are a major contribution to the lifetime equivalent fatigue loads for some components which could cause premature structural failure. As the size of the blades increase, the unbalanced loads increase and the frequency of the spectral peaks decrease. Hence, they have an increasing impact as the size of the turbines become bigger.

In this scenario, the demand for improvements in blade design is evident. The notion of increasingly mass efficient turbines, which are also able to harvest more energy, is immediately attractive.

The viability of a novel adaptive blade concept for use with horizontal axis WTs is studied in this project. By suitably tailoring the elastic response of a blade to the aerodynamic pressure it could be possible to improve a turbine's annual energy production, whilst simultaneously alleviating structural loads. These improvements are obtained in a passive adaptive manner, by exploiting the capabilities that structural anisotropy and geometrically induced couplings provide. In particular, induced elastic twist could be used to vary the angle of attack of the blade sections according to power requirements, i.e. the elastic twist is tailored to change with wind speed proportionally to the bending load. The adaptive behaviour allows the blade geometry to follow the theoretically optimum shape for power generation closely (which varies as a function of the far field wind speed). This concept retains the load alleviation capability of previously proposed designs, whilst simultaneously enhancing energy production. Structurally, the adaptive behaviour is achieved by merging the bend-twist coupling capabilities of off-axis composite plies and of a swept blade planform. Potentially, an adaptive blade, controlled only by generator torque, could perform to power standards comparable to that of the current state-of-the-art-while greatly reducing complexity, cost and maintenance of wind turbines, by challenging the need for active pitch control systems.

Planned Impact

Industry partners associated with the Supergen Wind Energy Hub will gain immediate access to our results noting the Hub provides an excellent conduit for facilitating impact. Additional beneficiaries include our specific project partners: Vestas Wind Systems, DNV GL and Offshore Renewable Energy (ORE) Catapult. Successful outcomes will lead to further development of manufacturing processes, potentially under Bristol's ownership of the National Composite Centre (NCC), itself part of the high-value Manufacturing Catapult. Bespoke industry days at both Bristol and Strathclyde will also foster wider dissemination with potential end-users.

Society, in general, will benefit by having access to cost-effective, more reliable energy from a sustainable, secure and UK-based means. Wind energy can be an emotive topic for society and we will endeavour to inform the public at large of the outcomes of our work and hopefully inspire new generations of engineers through our engagement events with schools.

The UK economy aligned with design and manufacture will also benefit by the upskilling and high-level training of postdoctoral researchers.

Academics will benefit from the knowledge developed in this proposal which will be disseminated through academic conference and journal papers.
 
Description 1. A new variable stiffness finite element for structural analysis of wind turbine blades.
2. A set of open access design tools for composite optimisation (Optibless)
3. An aeroelastic tool for wind turbine blades (ATOM)
Exploitation Route Our design tools for making composite structures are freely available
Sectors Aerospace, Defence and Marine,Energy,Manufacturing, including Industrial Biotechology,Transport

 
Description One of our project partners (ORE Catapult) placed a national call for a Wind Blade Research Hub. Our team applied for this centre and after submitting a proposal and interview, we were notified that we had won the competition in February 2017. We are currently negotiating terms. The total value of the Hub is approximately £2M with direct funds of £700k over 5 years from ORE Catapult. update 2019-The wind blade research hub has been running for 21 months now. We have 2 PhD students and 1 IDC student as well as one 1 postdoctoral researcher on it update-2020- The wind blade research hub has been running for 32 months. We have 4 PhDs, 2 IDC students and 2 postdoctoral researchers working on it
First Year Of Impact 2017
Sector Energy,Environment,Manufacturing, including Industrial Biotechology
Impact Types Economic

 
Description International Exchange Scheme
Amount £2,000 (GBP)
Funding ID IE160439 
Organisation The Royal Society 
Sector Charity/Non Profit
Country United Kingdom
Start 11/2016 
End 03/2017
 
Title Advanced Wind Turbine Optimisation Framework 
Description We develop a sophisticated optimisation framework for the optimisation of wind turbines. In particular, these tools and models have been developed in order to span a design search space much broader than that of conventional wind turbine designs. The developed tools combine state of the art models in composite optimisation, structural and aero-elastic analyses. 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact The models and optimisation algorithms developed as part of this project are state of the art design tools that will allow us to investigate key research question about wind turbine designs. In particular, we will be focusing on investigating the viability of bend-twist coupled blades in the near future. 
 
Description Pint of Science lecture 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact n/a
Year(s) Of Engagement Activity 2017,2018
 
Description Science week lecturer, Carlow Ireland 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Public/other audiences
Results and Impact n/a
Year(s) Of Engagement Activity 2018