Measurements in Rollup Region of the Tip Vortex from a Rectangular Wing

The evolving three-dimensional flowfield of the tip vortex in the near wake of a rectangular wing at incidence was studied in detail, using three-component laser Doppler velocimetry. The flow quantities measured were the three components of the instantaneous velocity. These data were used to obtain the distributions of velocity, vorticity, and circulation across the vortex at several axial locations in the flow for several angles of incidence. The data have been used to understand the process of rollup of the shear layer into the vortex in the near wake, as well as its kinematic structure. The data indicate that the rollup takes place quite quickly and the inner part of the three-dimensional vortex becomes nearly axisymmetric within a distance of about two chord lengths downstream of the trailing edge. Even though the vortex behavior in the near wake is, in general, strongly dependent on the initial conditions, the vortex trajectory appears to be described reasonably well by the overall wing lift and the freestream velocity. Also, even in the near wake, circumferentially averaged mean flow properties in the inner part of the nearly axisymmetric vortex begin to exhibit a universal structure characteristic of conceptual asymptotic trailing vortices