Measurements of the near Wake of a Rotor in Forward Flight

# Graduate Research Assistant, Student Member AIAA * Professor, Associate Fellow AIAA This paper describes initial measurements of the near wake of a 2-bladed teetering, untwisted, squaretipped rotor in forward flight. Issues of periodicity and repeatibility of the core are studied using laser velocimetry and flow-visualization on the front of the rotor wake where cycle to cycle variations are expected. Core passage uncertainty from cycle to cycle is less than 1 ̊ of rotor azimuth. Velocity measurements on the advancing blade side show wake-like core-axial velocities higher than the core circumferential velocity for the first 180 ̊ of vortex age. Both the axial and circumferential velocities approach 50% of blade tip speed. The inboard vortex sheet has substantial wake-like velocities and rolls up into a concentrated circulatory region of high wake-like axial velocity rotating opposite to the tip-vortex, within 30 ̊ from the blade. The fully-developed values of the vortex core circulation, radius and axial velocity remain constant over 180 ̊ of age as current measurements indicate. Measurements on the front, rear and retreating blade side of the rotor are in progress.