Effects of Ice Accretion on the Aerodynamic Performance and Wake Characteristics of an UAS Propeller Model

摘要

A comprehensive experimental study was performed to investigate the effects of ice accretion on the aerodynamic performances and wake characteristics of a UAS propeller model under different icing conditions (i.e., rime vs. glaze). The experimental study was conducted in the unique Icing Research Tunnel available at Iowa State University (ISU-IRT). In addition to acquiring the key features of ice accretion on the rotating propeller blade using a "phase-locked" imaging technique, the wake characteristics of the rotating UAS propeller under the different icing conditions were also resolved by using the Particle Imaging Velocimetry (PIV) technique along with the time-resolved measurements of aerodynamic forces and power consumption of the UAS propeller model. Both "free-run" and "phase-locked" PIV measurements were performed on the propeller model at different stages of the icing experiments (i.e., before, during and after the dynamic icing processes) to provide both the instantaneous flow characteristics and the ensemble-averaged flow statistics (e.g., mean velocity, vorticity, and turbulence kinetic energy) in the wake of the rotating propeller model. It was found that while the rime ice accretion would closely follow the original profiles of the propeller blades, the glaze ice was formed into very irregular structures (e.g., "lobster-tail-like" ice structures) that can significantly disturb the wake flow field of the rotating propeller model, generating the much larger and more complex vortices. Such complex large-scale vortices were found to enhance the turbulent mixing in the propeller wake and produce an evident velocity defícit channel around the outer board of the propeller blades, which provided direct evidences in elucidating the dramatic decrease in thrust generation and the significant increase in power consumption of the rotating propeller model in icing conditions. The findings derived from this study revealed the underlying mechanisms of the aerodynamic performance degradation of the iced UAS propeller, which is of significant importance for the development of innovative, effective anti-/de-icing strategies tailored for UAS icing mitigation and protection to ensure the safer and more efficient UAS operations in atmospheric icing conditions.