Experiment on the jet/trailing vortex interaction during the wake roll-up phase

A wind tunnel experiment explores the interaction between a parallel jet and the tip vortex from a rectangular wing with jet nozzles beneath, designed to mimic a cruising aircraft in terms of the propulsive-to-lift force ratio. The wake is investigated over the full roll-up phase of the trailing vortex sheet—about 20 wingspans—enabled by the tunnel’s long test section. A parametric study of the jet-to-wing-tip distance evaluates (i) the vortex influence on jet mixing, and (ii) the vortex response to the jet disturbance. Half of the symmetric wake is measured via stereo particle image velocimetry (PIV) in several transverse planes. Sufficiently downstream, the tip vortex dynamics appear largely unaffected by the jet, exhibiting growing oscillations (meandering) regardless of jet presence. The midwake region, associated with separated flow at the wing/mast junction, is found to promote transient horizontal oscillations. At the last measurement plane, the displacement mode aligns near 50◦, possibly indicating the onset of long-wave vortex instability, whose presence has yet to be fully ensured. Jet mixing is tracked using seeding in the same PIV planes. The jet is entrained by the rolling tip vortex, especially when positioned outboard near the vortex, producing a spiraling plume that enhances mixing. For very short jet-to-vortex distances, the jet becomes trapped in the vortex core. A model-based analysis of particle motion shows that tip vortex meandering has little effect on jet spreading.