Low Ice Adhesion Strength Coated Rotor Blades and the Effects of Surface Temperature on Ice Shedding

A study into the effects of a low ice adhesion strength coating and combined low power thermal heater system was conducted. Preliminary tests determined the mass of ice necessary to shed from the low ice adhesion strength coating at a specific ambient temperature (-4°C, -8°C, -12°C, and-16°C). The heater tests were conducted at an ambient temperature of -20°C, where the same mass of ice was accreted for each specific case temperature. With the accreted mass, the heaters were turned on until a shed event occurred. The surface temperature at the shed event was recorded. For colder temperatures such as -12°C and-16°C, the surface needed to reach a temperature within 1°C of -12°C and-16°C, respectively, to initiate a shed event. For the warmer cases the replication of ice at -20°C was not feasible, as the type of ice influences adhesion strength. Ice accreted at -20°C has different physical properties than ice formed at warm temperatures, therefore the surface temperature required for shedding did not match between the two tests. Results from the heater tests led to a discovery of a value that describes the adhesion strength normalized with respect to shed surface temperature. The value was found to be -1.09 psi/°C, averaged over six cases with varying conditions. This value is dependent upon a wide range of adhesion strength values for the system but opens possibilities of a full understanding of the hybrid thermal/passive coating system. With the experimental characterization of the adhesion strength to shed surface temperature value, future coating development could rely on heating the surface and recording the surface temperature needed for shedding. With such value, the ice adhesion strength of the coating could be characterized without the need for ice adhesion strength measurements.