Influence Of The Diffuser Geometry Of Shrouded Rotors On The Aerodynamic Footprint Of MAVs

Numerical simulations are conducted in order to assess the influence of diffuser geometry on the aerodynamic performance and aerodynamic footprint of shrouded rotors. The diffuser geometry varies in the azimuthal direction following a sine waveform with different wavelengths and amplitudes. It is shown that at a given rotor thrust, shroud thrust is reduced with respect to the optimized straight diffuser shape. For the specific cases addressed here, the reduction can simply be explained from simple potential flow theory / critical diffuser angle considerations as there is no clear evidence of strong induced three-dimensional effects. However, it is shown that wavy diffusers can help reduce the aerodynamic footprint of the rotor. This can potentially contribute to reducing brownout effects, thereby promoting flight capacity of MAVs operating in confined spaces through visual odometry.