Correlation Between Vortex Strength and Axial Velocity in a Trailing Vortex

The vorticesthat that trail from the wingtips of a large aircraft provide a significant hazardto an aircraft that follows in its wake. The objective is to contribute to the understanding of these vortices by identifying the conditions where an axial velocity in excess of the freestream value will be generated in the core of a trailing vortex. The axial velocity near the core of a trailing vortex was measured using a triple-sensor hot-wire probe and compared with measured values of vortex circulation strength. The vortex wasg eneratedin a wind tunnelusing a NACA 0015 wing model with a semispan aspect ratio of 0.80. A linear relationshipbetween the axial velocity and a nondimensional circulation parameter is indicated. For small values of the circulation parameter, the axial velocity shows a velocity deficit. An increase in circulation strength results in a progressive increase in axial velocity, which can exceed the freestream velocity by as much as 70%. The results indicate that the magnitude of the axial velocity is sensitive to the two end-cap configurations, flat and rounded, that were tested. It was found that scaling the circulation parameter by the vortex radius collapses the data from both configurations to a single linear curve.