An Experimental Study of Wake Vortex Instabilities

An investigation of the stability of a four-vortex wake has been conducted in the atmospheric boundary layer wind tunnel at the University of Notre Dame. Four independent wing models were used to create a generic four-vortex wake, such that the effects of circulation strength and vortex span could easily be studied. Helium bubble flow visualizations provide sufficient evidence of the persistence of a long-wavelength instability driven primarily by the strain field between the inboard-outboard vortex pair for a specific set of wake configurations. A quantitative investigation into the near-field development of these wakes via hot-wire anemometry further indicates the development of the elliptical form of short-wavelength instability. The experimental measurements of a short-wavelength perturbation frequency was found to compare favorably to that predicted by theory.