The Effects of Streamwise Vortex-Propeller Interaction on the Propeller Wake and Performance

In the development of Urban Air Mobility vehicles (UAMs), areas of concern include the stability of the vehicle and its aeroacoustic noise. Both issues are affected by vortex-propeller interactions. UAM propellers encounter large-scale vortices as they navigate through the transient flows within urban environments with tall buildings. In an effort to better understand the vortex-propeller interactions, this research focuses on the effects of streamwise vortex interactions with a propeller on the propeller performance and wake field. This study utilizes hotwire anemometry in a closed loop subsonic wind tunnel to measure the propeller wake and a load cell to measure the thrust produced by the propeller. The experiments involved generating a contra-rotating incident vortex (with respect to the propeller) using a stationary NACA 0018 wing of a 6-inch span pitched at 9°. The size and strength of the incident vortex were kept constant by conducting the experiments at constant freestream velocity, and fixed angle of attack and distance between the wing and the propeller. To characterize the size and dissipation of the wingtip vortex, a two-dimensional hotwire survey of the wing wake was conducted at various streamwise distances without the propeller. The propeller wake was also characterized separately to serve as a baseline. The effects of the ratio of the vortex diameter to the propeller diameter on the wake characteristics and wake performance are investigated. The changes in the wake due to the interactions with propellers of different pitch values are also investigated. The differences in flow characteristics of the propeller wake are visualized through contour plots, and the propeller performance is assessed through thrust and torque coefficients. The results indicate a more turbulent propeller wake with a velocity lower than the freestream velocity where the vortex interacts with the propeller.