An experimental study of rain erosion effects on a hydro-/ice-phobic coating pertinent to Unmanned-Arial-System (UAS) inflight icing mitigation

Abstract An experimental investigation was conducted to evaluate the variations of the surface wettability and ice adhesion strength on a typical hydro−/ice-phobic surface before and after undergoing continuous impingement of water droplets (i.e., rain erosion effects) at relatively high speeds (i.e., up to ~100 m/s) pertinent to Unmanned-Arial-System (UAS) inflight icing mitigation. The experimental study was conducted by leveraging a specially designed rain erosion testing rig available at Iowa State University. Micro-sized water droplets carried by an air jet flow were injected normally onto a test plate coated with a typical Super-Hydrophobic Surface (SHS) coating to simulate the scenario with micro-sized water droplets in the cloud impacting onto UAS airframe surfaces. During the experiments, the surface wettability (i.e., in the terms of static, advancing and receding contact angles of water droplets) and the ice adhesion strength on the SHS coated test plate were quantified as a function of the duration of the rain erosion testing. The surface topology changes of the SHS coated surface against the duration of the rain erosion testing were also measured by using an Atomic Force Microscope (AFM) system. The characteristics of the surface wettability and ice adhesion strength on the eroded SHS surface are correlated with the AFM measurement results to elucidate the underlying physics for a better understanding about the rain erosion effects on hydro−/ice-phobic coatings in the context of UAS inflight icing mitigation.