The far wake trajectory of the tumb領(lǐng) tip vortex effect of a reduced-scale, 1 m diame- ter, four-bladed rotor during hover is studied using vortex methods combined with a center of mass analysis approach. Measurements of all three components of the velocity field are acquired using a stereo PIV system synchronized to capture up to 800 wake age of the vortex with 10 offsets during hover conditions. The nominal operating condition of the rotor is at a rotational speed of 1520RPM, corresponding to Rec = 248,000 with a chord length of 58.5mm. The rotor was operated with a pitch of 7.2± 0.5 and a CT / of 0.029. The far wake vortex tumb領(lǐng) phenomenon is captured and described. It is shown that tip vortices from two blades tumble through approximately 180 of rotation before they coalesce. It is seen that the parent vortices are stronger than the daughter vortex, but due to vortex stretching the daughter vortex has a smaller radius with greater swirl strength. An accurate characterization and prediction of the trajectory of the far wake vortex tum- b領(lǐng) can enhance the ability to predict and alleviate the resuspension of particles during brownout as well as provide a database for far wake validation of CFD codes. 德國LaVision PIV/PLIF粒子成像測速場儀 自適應(yīng)粒子成像測速場儀（PIV） 三維立體PIV