Formation of a Trailing Vortex

Abstract

The incompressible flowfield in the vicinity of a l ift ing rectangular finite wing is investigated experimentally to ascertain the nature and detailed characteristics of the formation of a trailing vortex. The mean velocity field was mapped directly using a linearized constant temperature hot-wire anemometry probe in conjunction with a precision wind-tunnel traversing mechanism. The associated vorticity field was inferred from these measurements through a spatial contour integration procedure. The existence of several identifiable flow regions exhibiting similar characteristics was established and verified with both hot-wire and flow visualization data. The nature of the near surface bound vorticity distribution is described including a map of the Prandtl-bound vortex filaments. Measurements at the wing trailing edge show that the properly nondimensionalized characteristic vorticity distribution in this region is independent of angle of attack. Shed vorticity emanating from the lower aerodynamic surface near the wing tip was observed to roll up adjacent to the tip and roll over onto the upper wing surface at a chordwise location which depends on the wing orientation. The presence and behavior of this structure which possesses an identifiable core is suggested as the cause of the modified pressure distribution (l ift increment) normally observed in this region.