"Rotor Wake -Induced Flow Separation on a Lifting Surface"
Journal of the American Helicopter Society, Vol. 40, No.2, April 1995, p.
Susan M. Foley, Robert B. Funk, Phillip A. Fawcett , Narayanan M. Komerath.
Abstract: Fin buffeting, wing download, and degradation of stabilator effectiveness
have been observed on rotorcraft where the rotor wake interacts with these
surfaces. This Note describes the finding of flow separation induced by rotor
wake vortex interaction on a lifting surface at low angles of attack. The
flowfield is perturbed by varying the location and attitude of an upstream
lifting surface to confirm that the separation phenomenon is indeed real
and persists over a wide range of flow conditions. Though such upper-surface
flow separation is counter-intuitive at first glance, the phenomenon becomes
obvious when one is able to see the vortex interacting with the upper surface
flow field. This is enabled by laser sheet visualization. Surface pressure
variations are measured using microphones an static pressure taps. The 3-dimensional
unsteady nature of the separation is shown by videotaping tuft behavior on
the upper surface.
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