Drag Reduction by Manipulation of Afterbody Vortices

摘要

Drag force, surface pressure, and particle image velocimetry measurements were carried out in wind tunnel experiments in order to study the effect of minispoilers on the drag of an axisymmetric cylinder with a slanted base that has an upsweep angle of Phi = 28 deg. Two different spoiler heights (h/D=2.5 and 5%) were examined at various chordwise locations along the slanted surface. Placing the spoiler closer to the beginning of the slanted section caused an increased drag due to the separation induced by the spoiler itself, although a more diffused afterbody vortex was produced due to the turbulence ingestion. Drag reduction was observed when placing the spoiler closer to the trailing edge, with the optimum location x(s)'/c = 87.5%, resulting in approximately 5% drag reduction for both spoiler heights. This reduction was due to the displacement of the afterbody vortex away from the surface as the minispoiler acted similarly to a Gurney flap. The same effect can also be produced by introducing a smaller corotating vortex to manipulate the afterbody vortex trajectory.