A Study of the Trailing Vortices Behind a Ring Wing

Citation

Bofah, Kwasi Kete (1976) A Study of the Trailing Vortices Behind a Ring Wing. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/050Z-4228. https://resolver.caltech.edu/CaltechETD:etd-11092006-132109

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The flow field of a laminar vortex wake behind a ring wing was investigated. Experiments were conducted in the GALCIT Low Speed Water Channel, using laser Doppler velocimetry techniques to measure vertical and axial velocity components in the trailing vortex wake. A thin cylindrical ring wing model was tested at various axial angles of attack and free stream velocities. Velocity profiles were measured at several downstream stations from the trailing edge to 45 wing diameters downstream. The inviscid roll-up of the trailing vortex sheet shed by a ring wing was numerically examined. A line vortex representation was used to calculate the evolution of the initially cylindrical vortex sheet. The vortex sheet was found to distort in shape and then smoothly roll up into a pair of doubly connected spirals whose centers originate from approximately the center of gravity of vorticity in the upper quadrants of the ring wing's circular trailing edge. (This origin is at an angle of 38° measured from the horizontal wing diameter.) The experimental and flow visualization results are consistent with the numerical data and show that a pair of counter-rotating vortices do develop from the rolling up of the vortex sheet shed by a ring wing in a nonaxial flow. The vortices trail, downstream of the wing, with their vorticity centroids spaced by [...]/4 wing diameters. Saffman and Moore's theory of axial flow in laminar trailing vortices was adapted and found to be in reasonable agreement with the experimental results. The flow field near the trailing edge was found to be in fair agreement with Weissinger's inviscid calculations.

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