Three-dimensional wake interactions for two side-by-side cylinders in a cross flow

Three-dimensional (3D) flow over two side-by-side circular cylinders is numerically studied for understanding the complex wake interference behind the cylinder pair. The two cylinders are bounded by two spanwise end plates. A multiple-relaxation-time lattice Boltzmann method (MRT-LBM) is used for the solution of 3D unsteady flow. The simulations are carried out with Reynolds number Re = 200, aspect ratio L/D= 16 and four transverse pitch ratios: T/D=1.2, 1.5, 2.0 and 3.0, where Re is defined by incoming velocity U, cylinder diameter D and kinetic viscosity ν, L is cylinder span length and T is center to center spacing between the cylinder pair. Numerical results show that the wake patterns depend on not only Re and T/D, but also the end-flow conditions. At T/D = 2.0, the mutual interference between the two cylinders leads to two flip-flopping vortex streets; with the gap flow biased randomly, intermittently towards one cylinder or the other. Both the wake street and statistics of fluid force vary along the cylinder span considerably, indicating strong three dimensionality of the wake flows and their interaction.