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 blade frequency.

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