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Current Trends in the Application of Atmospheric Plasma for the Improvement of Wind Turbine Efficiency through Separation Control

Authors: Mei CheongDr. Maziar Arjomandi

Presenter: Amelia Greig

21st July 2011

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Wind Energy

• Clean alternative source of power • Currently competitive with fossil power • Major limitation comes from adverse aerodynamic

loadings shortening lifespans

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Price comparison between wind and traditional power. Courtesy of UTS

Wind turbine on Rottnest IslandCourtesy of Caniluna Pty Ltd

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Loads on Wind Turbines

• Inertial forces due to dead weight of rotor blades which are periodic and unsteady

• Aerodynamic loads – Uniform, steady airflows generate time-independent steady-

state loads

– Steady but spatially non-uniform airflows cause cyclic loadings

– Turbulent airflows cause non-periodic stochastic loads

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Aerodynamic Blade Loading

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Turbine velocity components and resulting angle of attack

• Two velocity components – wind and blade motion• Resultant gives optimal angle of attack

– Generally between 12o-15o

• Wind gusts up to 25%, alter required angle of attack

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Blade Separation and Stall

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Lift coefficient of turbine blade with angle of attack Adapted from http://www.sportpilot.org

Change in airflow with angle of attack

• Lift coefficient varies with angle of attack. Should be as high as possible for efficient turbine operation

• Wind gusts cause separation and stall to occur if angle of attack increases past maximum levels

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• Wind turbines designed to operate in specific ranges of wind speeds

• Outside this range, adverse aerodynamic loads occur predominantly due to separation control

• Turbine blade loads controlled through:– Flow velocity through variable speed rotor– Blade length– Blade incidence angle through variation of blade pitch– Blade section aerodynamics

Separation Control

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• Minimize fatigue life of system due to changes in wind direction and speed

• Passive control– Control through adaptation of aero-elastic

responses of blades and stall regulation

• Active control– Control through adjustment of aerodynamic

properties and pitch angles of blades

Load Reduction - Blade Section Aerodynamics

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Photos from http://www.lmwindpower.com and http://en.wikipedia.org

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Plasma Actuators

Schematic configuration for DBD actuator

8 Adapted from Cheong et al. 2010

• Plasma generated by applying an electric field to sustain electron-ion pairs

Electron movement: a) negative half-cycle, b) positive half-cycle

• Standard Dielectric Barrier Discharge (DBD) Actuator configuration

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Plasma induced airflow and response force

DBD Actuator Physics

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Adapted from Cheong et al. 2010

Plasma discharge

• Dielectric material retains more electrons than the electrode material resulting in an asymmetric flow pattern

• Induced airflow, called ‘Ionic Wind’ results

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• DBD actuators modify fluid flow characteristics by generating massless wall jets in the boundary layer of the flow

• Introduction of these jets injects momentum into retarded boundary layers to delay separation or even reattaching separated flow

Massless Wall Jets

Adapted from Nelson et al., 200810

Lift coefficient with and without actuator

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• DBD actuators were shown to – energize flow near locations of separation (Huang et al. 2006)– increase stall angle and delaying leading-edge separation (Orlov et

al. 2007, Post & Corke 2004)– improve lift cycle by controlling dynamic stall vortices (Post & Corke

2006)

DBD Actuators for Flow Separation

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Adapted from Post & Corke, 2006

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• DBD actuators are an effective means of separation and stall control

• Feasible method of load control for wind turbine blades

• Advantages over conventional methods of load control: High frequency responseDo not introduce parasitic dragLow power consumption

• Further investigations to implement DBD actuators on wind turbines highly valuable

Summary

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Acknowledgements

• Electrical and Mechanical Engineering Workshop at the University of Adelaide

• The Sir Ross and Sir Keith Smith Fund

DisclaimerResearch undertaken for this report has been assisted with a grant from the Smith Fund (www.smithfund.org.au). The support is acknowledged and greatly appreciated. The Smith Fund by providing for this project does not verify the accuracy of any findings or any representation contained in it. Any reliance in any written report or information provided to you should be based solely on your own assessment and conclusions. The Smith Fund does not accept any responsibility or liability from any persons, company or entity that may have relied on any written report or representations contained in this report if that person, company or entity suffers any loss (financial or otherwise) as a result.