Rotor Wake Interaction with a Lifting Surface"
Robert B. Funk and Narayanan M. Komerath.
Presented at the 51st Annual Forum of the American Helicopter Society, Ft.
Worth, TX, May 1995.
Abstract: Vortex interaction with wings and control surfaces causes unsteady,
three-dimensional flow separation phenomena which are only beginning to be
understood. An NACA0021 wing interacting with the wake from a 2-bladed teetering
rotor is used as a basic experimental configuration to study such phenomena.
Video images of surface tufts and smoke in pulsed light sheets, laser velocimetry
and surface pressure sensors are used to capture the primary features of
the interaction. The interaction is found to be periodic except during the
impingement of the vortices on the surface. Strong once-per-revolution pressure
fluctuations are shown to result from the divergence of vortex trajectories,
enhanced by surface interaction. Flow reversal is found upstream and under
regions of vortex interaction on the wing upper surface, and massive steady
separation is found on the lower surface. Vortex core flow stagnation on
the surface under the advancing blade side appears to cause an apparent "diffusion"
of vorticity seen in vorticity contours constructed from velocity data. Strong,
quasi-steady spanwise flow is caused downstream of vortex interaction. The
separation line moves rapidly over the surface. Integrated section pressure
distributions are dominated by the blade passage signature, periodic at the
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