An Experimental Study of the Wind-Driven Water Droplet/Rivulet Flows Over an Airfoil Pertinent to Wind Turbine Icing Phenomena

Abstract

Wind turbine icing represents the most significant threat to the integrity of wind turbines 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, an experimental investigation was conducted to characterize the surface wind-driven water film/rivulet flows over a NACA 0012 airfoil in order to elucidate the underlying physics of the transient surface water transport behavior pertinent to wind turbine icing phenomena. The experimental study was conducted in an icing research wind tunnel available at Aerospace Engineering Department of Iowa State University. A novel digital image projection (DIP) measurement system was developed and applied to achieve quantitative measurements of the thickness distributions of the surface water film/rivulet flow at different test conditions. The measurement results reveal clearly that, after impinged on the leading edge of the NACA0012 airfoil, the micro-sized water droplets would coalesce to form a thin water film in the region near the leading edge of the airfoil. The formation of rivulets was found to be time-dependent process and relies on the initial water runback flow structure. The width and the spacing of the water rivulets were found to decrease monotonically with the increasing wind speed. The film thickness icing scaling law is evaluated by the time-average measurement film thickness. The measurement results show good consistent with the analytical scaling predictions.