Pressure Fields Around a Rotor Blade in Reverse Flow

The flowfield and pressure distribution of a rotor blade in reverse flow is studied using stereoscopic particle image velocimetry. The 2-bladed teetering rotor with rigid NACA0013 untwisted untapered blades, with manually set collective and cyclic pitch, is operated at advance ratios from 0.7 to 1.0. Results are presented from azimuths 240 and 270 degrees, where the velocity field in chordwise sectional planes at two radial stations are analyzed, at two advance ratios. The paper is focused on two aspects. First is calculation of the total circulation around each blade section, and around the strong sharp-edge vortex seen below the blade in these sections. The second is the surface and flowfield pressures derived from the 3-component velocity field obtained from closely-spaced planes, after interpolation to satisfy the mass continuity equation. The pressure extraction technique is being developed using a yawed-cylinder test case, and shows good success in satisfying continuity between data planes.