Effect of a Jet on Vortex Merging

Abstract

Experiments were conducted in order to understand the effect of an axial jet on the merging process of a simulated flap-edge and wing-tip co-rotating vortex pair in the near wake. Cross-flow velocity measurements and flow visualization were performed for three realistic jet positions on both equal and unequal strength like-signed vortices for a range of momentum coefficients. The main finding was that the initial jet position has a vastly contrasting effect on the merging process. If the jet turbulence interacts rapidly with only one of the vortices, severe diffusion of that vortex occurs which ultimately wraps around and becomes consumed by the unaffected vortex structure. The jet causes a reduction in the vortex spacing and an increase in the rotation angle, hence merging is promoted. If the jet turbulence does not interact directly with either vortex, but instead interferes with the mechanism in the outer-recirculation region that advects vorticity to a larger radius, then merging can be retarded. In this case, an increase in vortex spacing and reduction in rotation angle was observed. Increasing the momentum coefficient, hence introducing more turbulence into the flow, has a greater effect on the merging process.