Optimizing the Layout of Heaters for Distributed Active De-icing of Wind Turbine Blades

Ice accumulation on wind turbines operating in cold regions reduces power generation by degrading aerodynamic efficiency and causes mass imbalance and fatigue loads on the blades. Due to blade rotation and variation of the pitch angle, different locations on each blade experience large variations of Reynolds number, Nusselt number, heat loss, and non-uniform ice distribution. Hence, applying different amounts of heat flux in different blade locations can provide more effective de-icing for the same total power consumption. This large variation of required heat flux highly motivates using distributed resistive heating with the capability of locally adjusting thermal power as a function of location on the blade. To optimize thermal actuation strategy, improving de-icing efficiency, and reducing power consumption, development of a numerical model was investigated for distributed resistive heaters using a computational approach with ANSYS. The numerical model was validated with experimental results. Then, ice melting was modeled on the blade for different heater layouts (aligned and staggered) and geometries. The result of this study showed more uniform and 40% faster de-icing, with approximately 30% reduction in the maximum applied temperature to the blade structure for circular heaters compared to square heaters. Furthermore, aligned heaters create relatively higher thermal stress to the blade structure than staggered heaters. This computational model can be used for the development of a pseudo-analytical aero-thermodynamic model for closed-loop active de-icing using distributed resistive heating on wind turbines and aircraft. Received 02/09/2013; Revised 13/09/2014; Accepted 23/09/2014 NOMENCLATURE AoA Angle of attack (deg) c Chord length (m) h Convective coefficient of heat transfer (watt/(m2·°C)) J De-icing performance cost function K Thermal conductivity (watt/(m·°C)) P Wind turbine rated power (watt) q input heat flux to the thermal resistor (watt/m2) qmax Maximum thermal resistor heat flux at maximum applied voltage (watt/m2) R Span-wise radius (distance from the hub) (m) Rtip Span-wise radius at the blade tip (m) T Temperature (°C) Tamb Ambient temperature (°C) Tc (t) Current blade surface temperature at time t (°C) Td Desired blade surface temperature (°C) Tmaxb Maximum global temperature on the surface of the blade during de-icing (°C) t Time (sec) tdi De-icing time (sec) uw Wind speed (m/sec) Vice Volume of ice residue (m3) VT>T0 Volume of the blade experiencing temperature higher than T0°C (m3) WIND ENGINEERING Volume 38, No. 6, 2014 PP 587–600 587 *S. Shajiee is a Ph.D. candidate in the Department of Aerospace Engineering Sciences, University of Colorado, Boulder, CO 80309. shervin.shajiee at colorado.edu †L. Y. Pao is the Richard and Joy Dorf professor in the Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, CO 80309. pao at colorado.edu ‡Robert R. McLeod is the Richard and Joy Dorf professor in the Department of Electrical, Computer, and Energy Engineering, University of Colorado, Boulder, CO 80309. robert.mcleod at colorado.edu