Numerical study of wake interference behind two side-by-side and tandem circular cylinders

We have developed a methodology to simulate flow at Re = 200 around two circular cylinders in side-by-side and in-line arrangements for spacing ratio between 1.5 and 4.0 Unsteady Navier-Stokes equations in terms of stream function and vorticity formulation are solved using the finite difference method. The wall stream function of each cylinder is solved iteratively from the constraint condition that derived from the surface pressure distribution is single-valued. When the spacing ratio is smaller than the critical value, markedly bistable biased gap flow is observed in the side-by-side cylinders, and intense interference of vortex shedding between two in-line cylinders appeared. Increasing spacing ratio beyond the critical value results in individual vortex shedding and simultaneous vortex shedding from two cylinders in the side-by-side case and the in-line case, respectively. Comparison of predicted lift, drag coefficients and Strouhal number with others numerical/experimental data, similar trend is obtained.