PIV Measurements of the Aerodynamic Interactions of Closely Spaced Phase Locked Propellers with Synchronized Rotation Rates

Emerging advances in electric-propulsion technology are enabling aircraft to use distributed electric propulsion (DEP) to increase efficiency and maneuverability. The implementation of DEP effectively decreases the spacing between propellers, introducing complex aerodynamic interactions that are not well understood. This study presents the use of stereoscopic particle image velocimetry to obtain 3D velocity measurements of the flow fields of phase locked and synchronized propellers at close proximity in a side-by-side configuration. The current study focuses on the hover configuration and flow field measurements were made over a plane that is located immediately downstream of the propellers. Single and dual propeller cases were explored at varying phase locked rotation angles. Variations of phase offset, separation distance, and rotation direction between the interacting propellers were explored. The total momentum thrust as a function of propeller phase angle was computed and used as a basis of comparison between the cases. It was found that the total instantaneous momentum flux of the dual propeller cases is a function of propeller phase angle, propeller spacing, and angular offset.