Wake characterization of thrust scaled counter-rotating coaxial rotor

The flowfield characterization of co-axial multi-rotor configuration in an out-of-ground (OGE) effect in hover is presented. A modular experimental setup with both axially and laterally adjustable rotor spacing is used for the study. Thrust scaled rotors each consisting of three blades actuated by DC brushless motors operating at torque balanced condition is being used. Collective pitch setting of the blades is changed to achieve the required trim condition. Flow visualization and time resolved particle image velocimetry (PIV) are used for the flow field characterization of the wake of the coaxial rotor system. The interaction between the wake and the tip vortices from the upper and lower rotor is studied in near and far wake by changing the axial separation distance between the rotors and keeping the tip Reynolds number constant. Non-dimensional axial separation distance is varied between 0.05-0.1 of the rotor diameter, which is the range in currently operational, full scale co-axial rotorcraft.