Experimental and numerical investigations on rotor noise in axial descending flight

We investigate the aerodynamic and aeroacoustic characteristics of a small-scale drone rotor operating in axial descending flight. The integrated aerodynamic forces and the far-field noise are measured by wind tunnel experiments. Then, near-field flow structures and corresponding noise source analysis are presented based on computational aeroacoustics (CAA) simulations. We found the unique acoustic feature of descending flight is the haystacking-like spectral humps, possibly caused by the interaction between the blade leading edge and the rotor wake.