Preliminary Investigation of the Role of the Tip Vortex in Rotary Wing Aerodynamics through Flow Visualization.
Technical rept. no. 1, 1 Jan 72-28 Feb 73,
SAGE ACTION INC ITHACA N Y
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The interaction between the tip vortices and successive rotor blades is responsible for two important helicopter problems, static loss in lift and blade slap during power descent. As a step toward the solution of these problems, the objective of this investigation was to examine the flowfield about an isolated blade in rectilinear flow up to 40 chords downstream. Wind tunnel tests were carried out on the tip section of a HR2S-1 S-56 blade in the NASA Langley VSTOL Research Wind Tunnel. Visualization of the detailed flow patterns, particularly the tip vortex and rollup in the near wake, was achieved using small, neutrally-buoyant bubbles as flow tracers. To provide adequate illumination, a new, expanded lighting arrangement was assembled from an array of searchlights. Also, a special chopper unit was designed and constructed for quantitative velocity data. Records of the flow patterns were made, both by means of still photography and a video system employing a high-sensitivity camera. Author