A computational study of flow past three unequal sized square cylinders at different positions

The flow past three unequal sized side-by-side square cylinders placed in different vertical configurations is investigated numerically using the lattice Boltzmann method for the Reynolds number Re = 160 and different values of the gap spacing between the cylinders, g, (ranging between 0.5 and 5). The present study is devoted to systematic investigation of the effects of cylinders position on the flow patterns. The reported results reveal that the flow patterns change significantly by the variation of cylinders configuration. Depending on the cylinders positions we observed; chaotic, base bleed, binary vortex street, modulated synchronized, inphase vortex shedding, antiphase vortex shedding, and in-antiphase vortex shedding flow patterns. The characteristics of the flow patterns are discussed with the aid of time history analysis of drag and lift coefficients, power spectra analysis of lift coefficients and vorticity contours visualization. The study also includes a detailed discussion on the aerodynamic forces, such as mean drag coefficient, Strouhal number and root-mean-square values of drag and lift coefficients. Our results show that the flow patterns behind three unequal cylinders are distinctly different compared to the flow past equisized square cylinders placed side-by-side. In chaotic flow pattern the secondary cylinder interaction frequency plays an important role especially at the second, third and fourth configurations for all gap spacings. At larger gap spacings for the first and sixth configurations, the primary vortex shedding frequency plays a dominant role and the jet effect almost diminishes between the cylinders.