Comparison of wake structures and force measurements behind three side-by-side cylinders

The research presents a numerical investigation of flow past three side-by-side square cylinders using the multi-relaxation-time lattice Boltzmann method. A comparison is made between equal and unequal gap spacings behind the three cylinders. Fluid forces acting on the cylinders, wake structure mechanism, time-trace analysis of drag and lift coefficients and vortex shedding frequencies are investigated systematically for different equal and unequal gap spacings. The Reynolds number is kept at 150 and unequal gap spacings (g1, g2) = (0.5, 0.6), (0.6, 0.5), (1.5, 1.6), (1.6, 1.5), (2.5, 2.6), (2.6, 2.5), (4, 4.1) and (4.1, 4) are selected for the investigation. For comparison we have also investigated the effect of equal gap spacings varied from 0.5 to 4. The results show that the wake structure and fluid forces are responsible for a slight change in gap spacing between any two cylinders. It is observed that the effects of unequal gap spacings on force statistics such as drag and lift coefficients, Strouhal number and the vortex shedding mechanism are notable at (g1, g2) = (0.5, 0.6), (0.6, 0.5), (1.5, 1.6) and (1.6, 1.5) and are completely different from those at equal gap spacings (g = 0.5 and 1.5). The results further show that at (g1, g2) = (4, 4.1) and (4.1, 4) the unequal gap spacing effect almost diminishes and only the primary vortex shedding frequency is observed. The bistable, asymmetric, inphase–antiphase and modulated synchronized flow patterns observed in this study.