In this study, the flow around three square cylinders with rounded corners in equilateral-triangular arrangements were investigated using the momentum exchange-based immersed boundary-lattice Boltzmann method (IB-LBM) at low Reynolds (Re) numbers. The influences of Re number and gap ratio delta to the flow characteristics, force coefficients, and Strouhal (St) number were examined by selecting one hundred different gap ratios delta and forty different Re numbers. The wake flow patterns are divided into six distinct categories according to the gap ratio, these are single bluff-body, deflected, flip-flopping, anti-phase, anti-phase & in-phase coexist, and fully devel-oped in-phase flow patterns. In addition, the Re number was also found to have a significant impact on the vortex shedding frequencies and flow properties. The drag coefficients, lift coefficients, and St number were calculated to demonstrate the relationship between vortex shedding properties, gap ratio, and Re numbers. The results revealed that the wake flow pattern, flow characteristics, and force coefficients depended significantly on the gap ratio and Re numbers. In addition, the power spectral density of the upstream cylinder were significantly lower than those of downstream cylinders for low gap ratios, and the mutual interference between each cylinders vanished as the gap ratio increased.
