VISUALIZATION OF THE WING-TIP VORTEX IN TEMPORAL AND SPATIAL PRESSURE-GRADIENTS

The evolution of the longitudinal vortex in the near field of a rectangular wing has been visualized using smoke and laser light sheet. The smoke photographs have been used to obtain qualitative and some quantitative information on the effect of small temporal and spatial pressure gradients on the evolution of the vortex in this region. The experiments indicate that even small temporal retardation of the flow can produce a significant increase in the vortex size. This effect becomes larger with increase in retardation, angle of incidence and distance downstream from the trailing edge. Also, vortex "breakdown" was found to occur in many temporal-deceleration experiments. The vortex evolution was, however, found to be relatively insensitive to the presence of small spatial adverse pressure gradients along the flow direction. The study is preliminary in nature and needs to be supported by more extensive quantitative measurements.