Analysis on three-dimensional flow characteristics of rotor wake

Abstract

As the main lift and control component of helicopters, the rotor has a complex flow field structure with unique characteristics, such as unsteadiness, paddle-vortex interference, and tip vortex. Thus, it is challenging to measure the rotor flow field. In addition, the instability of the flow is accompanied by strong flow pulsation, which leads to noise and blade vibration during the formation of tip vortices. A phase-locked Stereoscopic Particle Image Velocimetry (SPIV) technique, SPIV measurement technology, and phase locked technology are adopted in the present study to investigate the blade tip vortex. The blade tip vortex, which is the main flow structure to be characterized in this study about the rotor wake, is measured by the phase-locked SPIV technique. The velocity and vorticity fields at five phases are presented. Then, the main energetic modes of pulsation were extracted by proper orthogonal decomposition to analyze the instability characteristics of the flow. Finally, the three-dimensional structure of the blade tip vortex is reconstructed and presented. It can be seen that the blade tip vortex has a spiral structure and develops toward the rotor axis.