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Optimising the aerodynamic performance and control of wind turbines

Objective

The energy productivity of wind turbines is increasing through improvements in availability and design. Further gains may be expected but these will diminish as the energy extraction process approaches its limit. Consideration of the overall cost of energy is more important than the energy extraction process alone, and consequently, designs must be cost effective. Improved methods of control will reduce overall energy costs and the potential of two concepts which have shown promise in early tests will be studied. These are
Flap control
Airjet vortex generator control.
These retain the advantages of stall control but avoid problems associated with large actuator loads in a pitch controlled machine. Theoretical analyses and wind tunnel testing of these concepts will be effected. A blade set will be modified to test airjet vortex generators on a full-scale wind turbine. The targets include the optimisation of each concept, appraisal of their control characteristics, power curves and annual energy output.

Through the emphasis now being placed on renewable energy sources, the wind energy sector is receiving greater interest then ever before. Future wind turbines installed in Europe are likely to be of larger rotor size and greater efficiency to obtain the highest energy yield from the limited number of sites. Europe has a large number of private firms, research institutions, goverment agencies and electric companies working in the wind energy sector. The project must then have a European basis if this expertise is to be used to its greatest advantage.

Using a flap for aerodynamic control promises to combine the advantages of both stall and pitch control. The main objective is to compare flap control with existing aerodynamic control systems and compare loads and overall economy. A flap will provide precise control, simplified load paths reducing fatigue and rotor weight and requires lower actuating loads. The detailed tasks are
Define control concepts to be compared
Load calculations for specific critical load cases
Optimisation of flap design parameters
Verification of flap characteristics through wind tunnel testing
Outline design of rotor blade with flap
Power curve calculations and estimates of annual energy yield
Overall economic calculations for each concept
Airjet vortex generators may be another method of improving the performance and control of wind turbines.
Airjet vortex generators delay boundary layer separation and offer an increased lift to drag ratio over the upper half of the power curve.
Further gains may be realised in the post stall region if airjets can be used to tailor the power curve. The airflow for the airjets is available through natural pumping and the control system will be simple compared with pitch control. The detailed tasks are
Aerofoil selection from blade as used by wind turbine manufacturer
Design of airjet system using computational fluid dynamics
Optimisation of airjet system through wind tunnel testing
Performance calculations and estimation of annual energy yield
Detailed design of ducting and control strategies
Construction of blade test set
Erection and testing on full scale wind turbine
Analysis of operational results

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

CITY UNIVERSITY
Address
Northampton Square
EC1V0HB London
United Kingdom

Participants (3)

DEUTSCHES WINDENERGIE - INSTITUT GMBH
Germany
Address
Ebert Strasse 96
Wilhelmshaven
Ecotecnia Sociedad Cooperativa Catalana Ltd.
Spain
Address
23 1,Cl. Amistad
08005 Barcelona
Technische Universität Braunschweig
Germany
Address
Schleinitzstrasse
38106 Braunschweig