"Rotor Wake -Induced Flow Separation on a Lifting Surface"

Journal of the American Helicopter Society, Vol. 40, No.2, April 1995, p. 24 -

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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