An Experimental Investigation on Surface Water Transport and Ice Accreting Process Pertinent to Wind Turbine Icing Phenomena
Wind turbine icing represents the most significant threat to the integrity of wind turbines in cold weather. Ice accretion on turbine blades would decrease power production of the wind turbines significantly. Ice accretion and irregular shedding during wind turbine operation would lead to load imbalances as well as excessive turbine vibration, often causing the wind turbine to shut off. Icing issues can also directly impact personnel safety due to falling and projected large ice chunks. It should be noted that the icing hazard is often most severe in the locations which are best suited for wind turbine sites, such as northern latitudes, off-shore wind farms and high altitudes (i.e. mountains). Wind turbines in these regions are more prone to water contamination and icing in cold weather. Advancing the technology for safe and efficient wind turbine operation in atmospheric icing conditions requires the development of innovative, effective anti-/de-icing strategies tailored for wind turbine icing mitigation and protection. Doing so requires a keen understanding of the underlying physics of complicated thermal flow phenomena pertinent to wind turbine icing phenomena, both for the icing itself as well as for the water runback along contaminated surfaces of wind turbine blades. In the present study, a series of experimental investigations were conducted to characterize the transient behavior of wind-driven water film/rivulet flows over a NACA 0012 airfoil model and the dynamic ice accreting process over the airfoil model in order to elucidate the underlying physics of the important microphysical processes pertinent to wind turbine icing phenomena. The experimental study was conducted in an icing research tunnel available at Aerospace Engineering Department of Iowa State University. A suite of advanced flow diagnostic techniques, such as molecular tagging velocimetry and thermometry (MTV), digital image projection (DIP), and infrared (IR) imaging thermometry techniques, were developed and applied to achieve quantitative measurements of the film thickness distributions of the surface water film/rivulet flows and the temperature distributions of the water/ice mixture flows over the airfoil model surface at different test conditions. The new findings derived from the present icing physics study would lead to a better understanding of the important micro-physical processes, which could be used to improve current icing accretion models for more accurate prediction of ice formation and ice accretion on wind turbine blades as well as development of effective anti-/de-icing strategies tailored for safer and more efficient operation of wind turbines in cold weather.