The Effects of Vortex Interaction on Propeller Performance

Urban air mobility vehicles (UAMs), which are small flying taxis, promise to revolutionize city travel by offering a quick and environmentally friendly means of transportation. However, the uneven topology of the urban environments in which UAMs operate create large-scale, unsteady vortices that can disrupt the propellers of the small, light-weight UAMs. Utilizing a low-speed wind tunnel, this research aims to determine how vortices of different rotational directions impact the performance of propellers with varying diameters and pitches. A tip vortex was generated by a stationary wing with a NACA 0018 profile pitched at an absolute angle of attack of 9 degrees. Co-rotating or counter-rotating vortex (with respect to the propeller) are generated by pitching the wing at negative and positive angles of attack, respectively. Hotwire anemometry was used to locate the center of the vortex and measure its size at different streamwise locations, allowing for the alignment of the center of the propeller and the center of the vortex. The generated vortex interacted with a downstream propeller, whose thrust and torque outputs were measured with a load cell at varying rotational speeds. The effects of the vortex size with respect to propeller diameter and pitch are also investigated. The results show that a counter-rotating vortex will increase propeller thrust, whereas a co-rotating vortex will decrease propeller thrust. A co-rotating vortex will also decrease the torque applied to the motor while a counter-rotating vortex will increase the torque. These effects can be mitigated by decreasing the pitch of the propeller or by increasing the size of the propeller. These findings will assist engineers in adapting the designs of aircraft propellers and stabilization systems to account for vortex-propeller interactions in urban environments. Future research includes detailed flow field measurements using three-dimensional particle image velocimetry.