Interaction effects on blade tip vortices in a quadrotor μUAV in hover

The interaction of rotor wakes emanating from the blades of a multirotor micro unmanned air vehicle ( μ UAV) plays a crucial role in defining the performance and efficiency of the aerial platform. The current work leverages particle image velocimetry (PIV) to quantify the interaction effects in the wake of a commercially available μ UAV by addressing the modifications in the evolution and decay of blade tip vortices (BTVs), accounting for vortex meandering and the influence of the external shear layer. Three increasingly more complex configurations are comparatively assessed to help isolate the effect of the support plate and of the rotor-rotor interactions: the BTVs generated by an isolated rotor (IR) are compared with the ones generated by the isolated rotor placed on the support plate (IR-SP) and by the quadrotor (Q) configuration. The experimental investigation revealed that BTVs shed by the IR-SP and Q configurations undergo straining due to the influence of the support plate and experience premature dissipation. Additionally, the BTVs shed by the IR-SP and Q configurations exhibit, respectively, a 23% and a 51% reduction in circulation compared to the ones generated by the isolated rotor, even for very early vortex ages, indicating that significant interaction effects take place at the rotor disk level. Finally, BTVs shed by the IR-SP and Q configurations also show increased levels of aperiodicity, with the instantaneous vortex position scattering growing by factors of approximately 5 and 25, respectively, over the IR configuration.