Experiments on asymmetric vortex pair interaction with the ground

The interaction between the asymmetric vortex pair and the ground was experimentally investigated in a closed-circuit water channel for the current study. Particle image velocimetry tests were conducted to achieve the velocity measurements of flow fields at various crossflow planes. The vortex pair, with the reference circulation Reynolds number Re-Gamma approximate to 4490, was tested with various initial heights (h(0)/b(0) = 1.5, 1.0 and 0.5) and circulation ratios (lambda = 0.36:1, 1:0.36, 0.6:1, 1:0.6), with it being found that according to different interaction effects, the trajectory and merger of the vortex pair could be significantly affected. As the primary vortex pair approached the ground, a high turbulent kinetic energy region was observed between the secondary and primary vortical structures, which suggests violent interaction and accelerated circulation decay of the primary vortex. In addition, depending on the distribution of secondary vorticity and image vortices to the moving coordinate system, merging-promoting or -inhibiting effects were observed, which eventually affected the evolution of the primary vortex pair. Graphic abstract