Three-dimensional computations have been performed to study the effect of variation of cylinder size on flow characteristics of two cylinders in side-by-side arrangement. The RANS simulations are performed using the commercial solver, STAR-CCM+®. Effect of variation of diameter ratio (DR) between two cylinders at fixed gap ratio and moderate Reynolds numbers (Re = 2000) on hydrodynamic characteristics, such as drag and lift force coefficients as well as wake characteristics, such as Strouhal number (St) has been presented. The coupled interactions between the cylinders in side-by-side arrangements are studied by means of cross-recurrence plots. © 2020 American Institute of Physics Inc.. All rights reserved.