INBOARD SHEET ROLL UP OF THE WAKE OF A SMALL-SCALE ROTOR SYSTEM

Analysis of flow visualization data of the rotor wake behind a scale m odel helicopter rotor in level forward flight (mu = 0.15 and 0.23) at one thrust level (C-T = 0.0064) and zero flapping, confirmed the exist ence of tip vortices as well as vortices that were most likely created by the roll up of the outboard edge of the inboard vortex sheet The r otor system used in the present test consisted of a four-bladed, fully articulated hub and utilized blades of rectangular planform with a NA CA-0012 airfoil section. A laser light sheet strobed with selected rot or azimuth, and seeded with smoke, was used to visualize the flow. Qua ntitative measurements of the geometric location of the inboard vortex sheet roll up and tip vortices were obtained from video images of the illuminated flow. Data were obtained for light sheet planes located o n the retreating side of the rotor disk at y/R = -0.3 and -0.8.