Experimental Researches on Electric Thermal Anti-Icing Performance and Runback Icing

Runback icing may occur on a thermal anti-icing system when the system is not fully evaporated. Most researches focused on aerodynamic characteristics at simulated runback ice shape, and icing wind tunnel test was very limited, the runback icing process, surface temperature variation, power consumption were not fully understood. Electric thermal anti-icing performance and runback icing were researched in FL-61 icing wind tunnel, and mean volume diameter was 20 mu m, liquid water content was 0.5-2 g/m(3). An electric thermal heater was equipped on a NACA 0012 airfoil with length of 304.8 mm to simulate a thermal anti-icing system, which consists of airfoil, heat insulation, electric heater and surface, and the electric heater was controlled to maintain surface temperature a preset value. Tests were performed in dry air and simulated icing conditions, keeping the temperature, angle of attack, and mean volume diameter the same, but varying the free stream velocity and surface temperature leads to differences in the runback icing process. Videography of the runback process was captured, temperature and power consumption were measured during anti-icing process. Water running back and icing process was researched. Water film formed on the leading edge heated area, and became rivulets when running back. Rivulets turned into ice where surface temperature was lower than freezing, and ridge ice grew dramatically. A "clean zone" without water and ice was observed slightly before ice ridge, which was believed to be caused by the forward step separation induced by ridge. This clean zone phenomenon was analyzed by examining test photos and videos, partial rivulets ran spanwise instead of chordwise downstream before ridge, so the rivulets cannot reach ice ridge continuously, and less water collected by high ridge than the initial ridge. The "clean zone" was a coupled result of water film running, unsteady aerodynamics and ice ridge growth, careful close-up researches were suggested. Thermal anti-icing process was researched. Surface temperature and power consumption variation with time was analyzed, there were a rapid decrease of temperature and a sharp increase in power consumption when spray initiated during anti-icing test. Although leading edge surface was heated up to 36.7 degrees C, the system performed as a running wet thermal anti-icing system, and a full evaporated anti-icing system would consume more power and need higher surface temperature. Runback ice can be affected by anti-icing power and icing conditions, a large extent of runback icing from 6% to more than 40% chord length was observed.