The Effects of Freestream Turbulence on Edgewise Flight Fixed-Pitch Rotor Noise and Forces

The use of eVTOL vehicles as a means of urban transportation forces the fixed-pitch rotors to operate in high levels of atmospheric turbulence. This makes it imperative to understand the basic effects of freestream turbulence on rotor noise and forces. To analyze these effects, a fixed-pitch APC 9x6E rotor was operated in a range of edgewise flight conditions.  The experiments were conducted in the UF Anechoic Wind Tunnel Facility, which was outfitted to include three sets of passive grids for varying freestream turbulence conditions. The grid generated turbulence intensity and integral length scales were characterized with stereoscopic Particle Image Velocimetry (sPIV). sPIV measurements were also conducted above the rotor, operating in both clean and turbulent freestream conditions to investigate the effects of mean flow distortion on turbulence properties. The results showed that the mean induced flow to the rotor plane altered the turbulence statistics when compared to the baseline grid characterization measurements. The rotor forces and noise were also measured in similar conditions and the results indicated that the increased freestream turbulence intensity reduced rotor efficiency.