Deformable trailing edge flaps for modern megawatt wind turbine controllers using strain gauge sensors

The present work contains a deformable trailing edge flap controller integrated in a numerically simulated modern, variablespeed, pitch-regulated megawatt (MW)-size wind turbine. The aeroservoelastic multi-body code HAWC2 acts as a component in the control loop design. At the core of the proposed controller, all unsteady loads are divided by frequency content. Blade pitching and generator moment react to low-frequency excitations, whereas flaps deal with high-frequency excitations. The present work should be regarded as an investigation into the fatigue load reduction potential when applying trailing edge flaps on a wind turbine blade rather than a conclusive control design with traditional issues like stability and robustness fully investigated. Recent works have shown that the fatigue load reduction by use of trailing edge flaps may be greater than for traditional pitch control methods. By enabling the trailing edge to move independently and quickly along the spanwise position of the blade, local small flutuations in the aerodynamic forces can be alleviated by deformation of the airfoil flap. Strain gauges are used as input for the flap controller, and the effect of placing strain gauges at various radial positions on the blade is investigated. An optimization routine minimizes blade root fatigue loads. Calculations are based on the 5 MW reference wind turbine part of the UpWind project primarily with a mean turbulent wind speed close to rated power. A fatigue load reduction of 25% in the blade root moment was obtained for a continuous 6.3 m long flap. Copyright © 2009 John Wiley & Sons, Ltd.

[1]  G.A.M. van Kuik,et al.  State of the art and prospectives of smart rotor control for wind turbines , 2007 .

[2]  Helge Aagaard Madsen,et al.  A near wake model for deformable trailing edge flaps implemented the in multi body aero-servo-elastic code HAWC2 , 2010 .

[3]  J. G. Leishman,et al.  Unsteady aerodynamics of a flapped airfoil in subsonic flow by indicial concepts , 1995 .

[4]  Christian Bak,et al.  Potential load reduction using airfoils with variable trailing edge geometry , 2005 .

[5]  Raymond Chow,et al.  Computational Investigations of Small Deploying Tabs and Flaps for Aerodynamic Load Control , 2007 .

[6]  H. Madsen,et al.  A Beddoes-Leishman type dynamic stall model in state-space and indicial formulations , 2004 .

[7]  Torben J. Larsen,et al.  Active load reduction using individual pitch, based on local blade flow measurements , 2005 .

[8]  Load Alleviation on Wind Turbine Blades Using Variable Airfoil Geometry , 2005 .

[9]  J. Gordon Leishman,et al.  Unsteady lift of a flapped airfoil by indicial concepts , 1994 .

[10]  Christian Bak,et al.  Implementing a Dynamic Stall Model for Airfoils with Deformable Trailing Edges , 2008 .

[11]  Ervin Bossanyi,et al.  Wind Turbine Control for Load Reduction , 2003 .

[12]  D. Weihs,et al.  The Effect of Chordwise Flexibility on the Lift of a Rapidly Accelerated Airfoil , 1979 .

[13]  Helge Aagaard Madsen,et al.  A near wake model for trailing vorticity compared with the blade element momentum theory , 2004 .

[14]  Mac Gaunaa,et al.  Wind tunnel test on wind turbine airfoil with adaptive trailing edge geometry , 2007 .

[15]  Mac Gaunaa,et al.  Load alleviation on wind turbine blades using variable airfoil geometry , 2006 .

[16]  Imad Abdallah.  Advanced load alleviation for wind turbines using adaptive trailing edge geometry : Sensoring techniques , 2006 .

[17]  Michel Verhaegen,et al.  On the proof of concept of a ‘Smart’ wind turbine rotor blade for load alleviation , 2008 .

[18]  Lars Christian Henriksen,et al.  Integrating deformable trailing edge geometry in modern Mega-Watt wind turbine controllers , 2008 .

[19]  Christian Bak,et al.  A dynamic stall model for airfoils with deformable trailing edges , 2009 .

[20]  Berend G. van der Wall,et al.  Experimental and Numerical Investigations on Steady and Unsteady Behaviour of a Rotor Airfoil with a Piezoelectric Trailing Edge Flap , 1999 .

[21]  Niels Troldborg,et al.  Computational Study of the Risø-B1-18 Airfoil with a Hinged Flap Providing Variable Trailing Edge Geometry , 2005 .