Simulation of three-dimensional flow around a square cylinder at moderate Reynolds numbers

Direct numerical simulations of two-dimensional (2D) and 3-D unsteady flow around a square cylinder for moderate Reynolds numbers (Re = 150-500) are p erformed, employing an implicit fractional step method finite-volume code w ith second-order accuracy in space and time. The simulations, which are car ried out with a blockage ratio of 5.6%, indicate a transition from 2-D to 3 -D shedding flow between Re = 150 and Re = 200. Both spanwise instability m odes, A and B, are present in the wake transitional process, similar to the how around a circular cylinder. However, seemingly in contrast to a circul ar cylinder, the transitional flow around a square cylinder exhibits a phen omenon of distinct low-frequency force pulsations (Re = 200-300). For 3-D s imulations, the Strouhal number and the mean drag coefficient are in genera l agreement with existing experiments. Between Re = 300 and 500, an increas e in the spanwise coupling of fluctuating forces is indicated. The influenc e of the spanwise aspect ratio using periodic boundary conditions, a finer grid, and a finer time step is also investigated (C) 1999 American Institut e of Physics. [S1070-6631(99)00902-2].