Tuesday, 27 September 2016
17:00 - 18:30 Innovative rotor design
Turbine technology  
          

In the conversion of wind power, the rotor is the first point of energy transformation, transforming the kinetic energy of the wind into torque and rotation. Rotor technology sets a limit of the energy converted and the loading required to convert this energy. The load cycles are design drivers, influencing the mass and operation of the rotor, and therefore the entire turbine. In addition to extracting kinetic energy from the flow, the rotor creates a pressure field that generates the wake and leads to noise generation. Rotor design optimisation must therefore account for power and load optimisation, constrained by the full lifecycle, fatigue life and noise, among other boundary conditions. This session focus on innovations in both rotor design methodologies and components.

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Learning objectives

• Understand the effect of geometric non-linearities in the fatigue life of the blade;
• Evaluate the possible impact of flexible certification guidelines in rotor design optimisation;
• Analyse the application of trailing edge serrations as a noise reduction device;
• Evaluate the potential of active flap control for both alleviation and power optimisation;
• Evaluate the impact of integrating the turbine lifecycle in the design optimisation of rotors.

This session will be chaired by:

Christian Frank Andersen LM Wind Power, Denmark
Co-authors:
Christian Andersen (1) ^F
(1) LM Wind Power, Kolding, Denmark

Rotor design approach for extending wind turbine platform lifecycle

Introduction

There is a clear trend in the wind energy market that the segment of 3-3.5MW wind turbines will grow significantly in the coming 5 year period. The growth of the segment will amongst other be supported by expansion into areas of lower wind classes, or regional specific wind climates, which drives a need for larger rotors to ensure a lower LCOE.

Approach

The growth in the 3-3.5MW segment will highly be supported by existing turbine platforms being upgraded.
As to upgrades of existing turbine platforms the challenge will be to optimize the annual energy production while still manage the loads on the various turbine components and thus minimize impact and need for major turbine component redesign. To overcome the challenge a design approach with high degree of freedom, which allows for balancing the load impact, is needed.


Main body of abstract

The overall optimization objective for rotor blade development is to reduce the cost of energy (COE). As the blades extract the energy from the wind, they are a critical component for reducing COE. There are different parameters that affect the blades contribution to COE, where some of the most important are the annual energy production, cost, and reliability. For on-shore turbines further design constraints have to be considered like transportability (e.g. blade chord) and noise emission. When designing rotors for existing wind turbine platforms also other parameters becomes dominant, like aero elastic response, as it will have a high impact on the turbine component loading, as such leaving a more narrow design window for the rotor design.
To optimize the aerodynamic performance and loads, there is a range of validated airfoils available, providing the characteristics needed for the specific rotor design. For the outer part of the blade, where the major part of the power production is generated, characteristics like aerodynamic efficiency and robust performance is prioritized, whereas on the inner part of the blade also the ability to support the structural efficiency have to be considered. Further to improve the aerodynamic characteristic, power as well as acoustics, enhancement devices are designed actively in.
To meet the wind turbine design constraints, the focus in the rotor design have to be kept equally important on the aerodynamic performance, as well as on the structural response of the rotor. The structural response of the rotor is influenced by several parameters: airfoil choice, blade plan-form, blade thickness distribution, layout of the blade structure and material choice (glass fiber or carbon hybrid). Further parameter to actively include when tailoring the structural response of the rotor is the blade pre-bend shape.
By tailoring of the blade pre-bending, the shape of the loaded blade is designed to be optimal in a load balance perspective. By advanced modelling of the aero-elasticity behaviour of the blades, it is possible to optimize the shape of the blades pre-bending, to reduce specific critical loading on other turbine components. Understanding the blade response during the life time of the turbine, together with the damage contributions, a shape can be designed, minimizing the damage of a set of chosen turbine components.


Conclusion

Designing optimized blades for existing wind turbine platforms will extend the product life cycle of the wind turbine. By tailoring the aerodynamics, and aero-elastic response, the annual energy production is optimized while utilizing the turbine component capabilities. The turbine components remain utilizing their efficient supply chain, and overall it supports the optimization of cost of energy.


Learning objectives
This presentation will show examples of complex blade design problems, where the aero elastic response of the blade have been constrained within a narrow window, to meet the wind turbine component design constraints, and how this have been overcome in the blade design approach, with a remained focus on a high performing rotor.