Rotorwash Characterization of a Counter-rotating Co-axial Rotor System

Abstract

An experimental investigation of the rotorwash generated by a counter-rotating coaxial rotor system was conducted by using a modular and thrust scaled experimental rig. The studies were carried out for in-ground-effect condition by varying the height of the rotor system above the ground for two axial separations of the coaxial rotor system. Comparisons were made between isolated single rotor and torque matched coaxial rotor configurations to study the effects of rotor interactions on the downwash and outwash for in-ground conditions. High-speed Particle Image Velocimetry (PIV) was used to measure the temporally resolved velocity field of the rotor wake and its interaction with the ground. Both time averaged and instantaneous characterization of the transition and outwash region of the coaxial rotor wake for in-ground conditions is investigated. The self-similar characteristics of the time-averaged outwash velocity across all operating conditions is explored. The effects of the time-averaged outwash velocity on the PAXman model and the spatio-temporal interactions of tip vortex structures in the transition and outwash region for coaxial rotors are discussed.