A numerical study is performed to investigate the effects of spacing ratio on the three-dimensional unsteady flow dynamics and axis-switching behavior of in-phase circular twin synthetic jets (TSJs) using Improved Delayed Detached Eddy Simulation. The simulations were performed at a fixed Reynolds number (Re=130) and dimensionless stroke length (L0/d=15.7), across four spacing ratios (s/d=1.2, 2.0, 3.0, and 4.0). The study uses time- and phase-averaged statistics, Q− criterion, and vortex circulation to characterize the evolution of vortical structures and jet-to-jet interference. The results show that jet interactions are enhanced as the spacing ratio decreases, promoting earlier merging of inner shear layers and the formation of coherent vortex ring pairs. The merging and combined points increased linearly with increasing spacing ratio. An axis-switching phenomenon, typically associated with non-circular jets, is induced in the circular TSJs through vortex interactions occurring at low spacing ratios (s/d≤3.0). As a result, the mean velocity decay, lateral spread rates, and vorticity redistribution in the TSJs are enhanced as the spacing ratio decreases.
Opoku-Mensah et al. (Sun,) studied this question.