An experimental study on the aerodynamic performance degradation of a UAS propeller model induced by ice accretion process

An experimental study was performed to investigate the effects of ice accretion on the aerodynamic performances and wake characteristics of a propeller model used for Unmanned-Aerial-System (UAS) 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 important 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 the 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. To the best knowledge of the authors, this is the first work of its kind to provide detailed, temporally-resolved wake flow field measurements of UAS propeller under real icing conditions. It is found that while the rime ice accretion could closely follow the original profiles of the propeller blades, the glaze ice usually forms into very irregular 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 are found to enhance the turbulent mixing in the propeller wake and produce an evident velocity deficit channel around the outer board of the propeller blades, providing 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 are believed to be essential and very helpful to elucidate the underlying mechanisms of the aerodynamic performance degradation of ice accreting UAS propellers.