Aerodynamic Design of Wind Turbine Blades Utilising Nonconventional Control Systems

Wiratama, I. Kade (2012) Aerodynamic Design of Wind Turbine Blades Utilising Nonconventional Control Systems. Doctoral thesis, Northumbria University.

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Abstract

As a result of the significant growth of wind turbines in size, blade load control has become the main challenge for large wind turbines. Many advanced techniques have been investigated aiming at developing control devices to ease blade loading. Individual pitch control system, adaptive blades, trailing edge microtabs, morphing aerofoils, ailerons, trailing edge flaps, and telescopic blades are among these techniques. Most of the above advanced technologies are currently implemented in, or are under investigation to be utilised, for blade load alleviation. The present study aims at investigating the potential benefits of these advanced techniques in enhancing the energy capture capabilities rather than blade load alleviation. To achieve this goal the research is carried out in three directions: (i) development of a simulation software tool suitable for wind turbines utilising nonconventional control systems, (ii) development of a blade design optimisation tool capable of optimising the topology of blades equipped with nonconventional control systems, and (iii) carrying out design optimisation case studies with the objective of power extraction enhancement towards investigating the feasibility of advanced technologies, initially developed for load alleviation of large blades, for power extraction enhancement. Three nonconventional control systems, namely, microtab, trailing edge flap and telescopic blades are investigated. A software tool, AWTSim, is especially developed for aerodynamic simulation of wind turbines utilising blades equipped with microtabs and trailing edge flap as well as telescopic blades. As part of the aerodynamic simulation of these wind turbines, the control system must be also simulated. The simulation of the control system is carried out via solving an optimisation problem which gives the best value for the controlling parameter at each wind turbine run condition. Developing a genetic algorithm optimisation tool which is especially designed for wind turbine blades and integrating it with AWTSim, a design optimisation tool for blades equipped with nonconventional control system is constructed. The design optimisation tool, AWTSimD, is employed to carry out design case studies. The results of design case studies reveal that for constant speed rotors, optimised telescopic blades are more effective than flaps and microtabs in power enhancement. However, in comparison with flap and microtabs, telescopic blades have two disadvantages: (i) complexity in telescopic mechanism and the added weight and (ii) increased blade loading. It is also shown that flaps are more efficient than microtabs, and that the location and the size of flaps are key parameters in design. It is also shown that optimisation of the blade pretwist has a significant influence on the energy extraction enhancement. That is, to gain the maximum benefit of installing flaps and microtabs on blades, the baseline blades must be redesigned.

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