In order to investigate the flowfield and aerodynamic characteristics of rotor in descent and vortex ring state

a BO-105 model rotor with tip Mach number similarity was tested in Φ5m vertical wind tunnel of China Aerodynamics Research and Development Center. Flowfields around blade tip in hover and descent flight were captured

and variations of rotor thrust and torque were obtained. The process of vorticity accumulation with the increase of rotor descent rate was observed through application of high speed PIV(particle image velocimetry) camera. When vertical descent rate was 0.9

rotor thrust and torque were at the lowestlevel

and the value was only 60% and 80%

respectively

of that in hovering state. The formation and break down of large scale vortex structure were observed in deep vortex ring state. Violent fluctuation of rotor thrust and torque in vortex ring state was caused by this phenomenon. Oblique descent had less thrust and torque loss than vertical descent. Aerodynamic characteristics of parabolic blade tip were similar with those of conventional rectangular blade tip in vertical descent.