Towards early ice detection on wind turbine blades using acoustic waves Viktor Berbyuk*, Bo Peterson, Jan Möller Department of Applied Mechanics, Chalmers University of Technology SE-412 96, Gothenburg, SWEDEN ABSTRACT The study focuses on the early detection of ice using controlled acoustic waves propagating in the wind turbine blades. An experimental set-up with a cold climate chamber, a composite test object used in turbine blades and equipment for glaze and rime ice production has been developed. Controlled acoustic waves are generated by magnetostrictive Terfenol-D based actuator. The propagation of three orthogonally polarized acoustic waves was studied by means of 6 accelerometers positioned, 3 each, in 2 holders on the 8 m long composite test object. The results show that for the considered composite test object the formation of ice, the ice mass, icing areas and the temperature have a significant influence on controlled acoustic waves propagation w.r.t. Fourier transform, amplitude attenuation and RMS values as indicators concluding that the proposed acoustic wave technique is a promising approach for ice detection. Keywords: Ice detection, controlled acoustic waves, composite material, rotor blade, wind turbine, magnetostrictive actuator 1. INTRODUCTION The output of the wind turbine is strongly influenced by the environment. In places with a cold climate wind turbines are affected by icing. Icing is one of the main contributes to the low performance of the wind turbine. Even a thin layer of ice can strongly influence the boundary layers at the surface of the turbine blade and decrease the lift coefficient and increase the drag coefficient considerably 1 . Due to these factors the wind turbine can lose power. In fact according to simple propeller theory the power loss will be directly proportional to the change in lift and drag coefficients if their relative changes are the same. However, since the drag coefficient is more strongly influenced the situation is much worse in practice. Somewhat greater ice layers can cause unbalance and influence the life time of bearings in various places of a wind turbine. Big chunks of ice can become loose and thrown away long distances and constitute hazard to lives for humans and animals. Really great ice buildup can of course wreck the entire wind turbine installation in a short time. In very rare cases the ice can even build a slat on the blade's leading edge. This is a high lift devise (usually combined with a slot) used on aircraft wings in order to increase the lift. Hereby the wind turbine can, by utilizing the higher lift, produce more energy than it was designed for and several types of difficulties can arise dependent on the control system. It is possible to use a deicing system but both starting deicing to late and too early can turn out to be costly. The later fact is related to the detrimental influence on the construction material in the blades due to some methods of deicing and the cost of deicing itself. A sensor system applied to the blades of the turbine could detect ice and start a deicing system before power losses are already measured on the output of the generator. A sensor system can be built on different principles such as optical, acoustical, others. A review on ice detection sensors and others ice related issues for wind turbines can be found in 2-4 . Acoustic waves have been used in nondestructive testing of isotropic materials since a long time. In this area one is usually looking for defects, cracks etc. Originally these studies were made using bulk waves. Later in order to study slender bodies one has started using guided waves (which can be seen as a sum of bulk waves) 5,6 . An example of such *viktor.berbyuk@chalmers.se; phone: +46 31 772 1516; fax: +46 31 772 3827; www.chalmers.se Nondestructive Characterization for Composite Materials, Aerospace Engineering, Civil Infrastructure, and Homeland Security 2014, edited by H. Felix Wu, Tzu-Yang Yu, Andrew L. Gyekenyesi, Peter J. Shull, Proc. of SPIE Vol. 9063, 90630F · © 2014 SPIE · CCC code: 0277-786X/14/$18 · doi: 10.1117/12.2046362 Proc. of SPIE Vol. 9063 90630F-1