Fluid Dynamics of Flow Around Side-by-Side Arranged Cylinders

Abstract

Flow past four side-by-side identical square cylinders arranged normal to the flow have been found to show interesting and important flow features which are very difficult to get through experiments. Lattice Boltzmann method (LBM) is used for numerical simulations of two-dimensional (2D) flow around four side-by-side arranged cylinders. In this study, the Reynolds number (Re) is chosen to be 60, 80, 100, 120 and 140 and the spacing ratio g* (= g/D, where D is the size of cylinder and g is the distance between the cylinders) is set at 0, 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 2.5, 3, 3.5 and 4. Based on the flow characteristics, seven distinct and unique flow regimes are identified for different ranges of Re and g*. Physical features of each flow regime such as wake structures, vortex dynamics, gap flow behavior, time histories of lift coefficients, shedding frequencies and hydrodynamic forces are thoroughly discussed. The Reynolds numbers strongly affect the flow, especially at 0 ≤ g* ≤ 2, in terms of vortex-shedding frequency. A significant secondary frequency is also found other than the primary frequency in the base-bleed and flip-flopping flow regimes. It is observed that for g* ≥ 2.5 primary shedding frequency strongly affects the flow dynamics and the mutual interaction of the wakes behind the cylinders decreases with an increase in the Reynolds number. The Strouhal value is same for the outer and inner cylinders in inphase–antiphase weak interaction flow regime and different for base-bleed and flip-flopping flow regimes. In inphase asynchronous weak interaction flow regime, the Strouhal number is same for all four cylinders.