This study investigates the three-dimensional interaction between a counter-rotating vortex pair subject to Crow instability and a flat wall in ReΓ=2500, 4000, and 6000 at h/r0=5.0, 10.0 (where h denotes the distance from the vortex center to the wall and r0 is the separation between the two vortex cores). The analysis combines quantitative measures, including total kinetic energy and enstrophy, with three-dimensional vortex-structure visualization based on the Q-criterion and helicity distribution, in order to elucidate the physical mechanisms governing vortex decay, reorganization, and breakdown. The results show that h/r0 determines the morphological evolution pathway of the vortex system as it approaches the wall. For h/r0=5.0, early interaction with the wall substantially alters the vortex dynamics compared with the unbounded case, leading to the formation of characteristic vortex tongues. In contrast, for h/r0=10.0, the Crow instability has sufficient time to fully develop and complete the reconnection process, forming a sequence of reconnected vortex rings prior to wall interaction. In addition, the effect of ReΓ manifests itself through a clear transition between different dynamical regimes. At ReΓ=2500, vortex decay is dominated by viscous diffusion. At ReΓ=4000, vortex stretching and three-dimensional (3D) twisting become significant, promoting the breakdown of the vortex system into hairpin vortices. At ReΓ=6000, the system undergoes a strong breakdown process, characterized by a sharp increase in enstrophy and the formation of a dense network of small-scale vortex structures, reflecting an intense transfer of energy from large to small scales. The helicity distribution is identified as an effective indicator of local 3D twisting intensity and the onset of coherent-structure breakdown. In particular, in ReΓ=4000–6000, a resonant twisting mechanism between the primary and secondary vortices is recognized as the main driver of scaly shaped structures and the collapse of vortex cores. Moreover, at ReΓ=6000, a figure-eight-shaped structure emerges in the trough region and undergoes a severing process at its neck, resulting in complete detachment from the original vortex system. These findings provide new insights into the decay dynamics of near-ground vortex wakes and are relevant to vortex-wake management problems in aviation.
Nguyen et al. (Mon,) studied this question.