In-cloud ice accretion and performance degradation of UAV propellers in forward flight: An experimental study
Manaf Muhammed, Derek Harvey, Hassan Abbas Khawaja, Muhammad S. Virk, Gelareh Momen
Abstract
An experimental study of ice accretion on a rotating UAV propeller blade was conducted under diverse environmental conditions. This research aimed to study the effects of varying independent environmental parameters on the characteristics and morphology of the accreted ice as well as its influence on propeller's performance. These experiments were carried out at the Anti-icing Materials International Laboratory (AMIL) Icing Wind Tunnel (IWT) at the Université du Québec à Chicoutimi (UQAC), Canada. The icing conditions are determined in accordance with the 14 CFR Part 29 Appendix-C for rotorcraft operating at altitudes below 10,000 ft. The analysis of results revealed that increase in Liquid Water Content (LWC) values can significantly affect the ice accretion rates. Higher LWC intensifies ice accretion, leading to a sharp initial drop in thrust and a rapid rise in power demand; however, it is observed that these variations gradually saturate after the initial aggressive degradation phase. Increasing Median Volume Diameter (MVD) can significantly affect the nature, morphology, and mass of accreted ice. The thin propeller sections were highly sensitive to increase in droplet size, leading to increase collection efficiencies. In some cases, an increase in MVD could trigger a transition in the ice accretion regime from rime to glaze ice. Also, the ice transitioned from soft rime to hard glaze as atmospheric temperatures approached the freezing point. Such transitions resulted in significative increase in the severity of the aerodynamic performance degradation. Elevated values of LWC and MVD at temperatures close to the freezing point led to the development of severe ice formations characterized by ice horns along the leading edge, intricate ice structures near the blade tip and fast degradation of aerodynamic performance. During ice accretion, thrust decreases linearly, while input power increases quadratically with RPM. The 3D scans of the final ice shapes obtained in this research not only offered detailed insights into the ice morphology but will also serve to validate numerical ice accretion models in future work. Performance penalties were notably more significant during the first 50 s of ice accretion, indicating a necessity for ice protection systems with low reaction times in rotary wing UAVs.