Laminar flow past two rotating circular cylinders in a side-by-side arrangement

For the purpose of a careful analysis of the modification of flow by the combined effects of the rotation and the spacing between two cylinders on the flow, numerical simulations are performed at a various range of absolute rotational speeds (vertical bar alpha vertical bar <= 2) for four different gap spacings of 3, 1.5, 0.7, and 0.2 at one Reynolds number of 100 showing the typical two-dimensional vortex shedding. As vertical bar alpha vertical bar increases, flow becomes stabilized and finally a steady state beyond the critical rotational speed depending on the gap spacing. In the cases of gap spacings of 3 and 0.2, the wake patterns keep the antiphase-synchronized pattern and the single bluff body pattern, respectively, until flow reaches the steady state. However, for the gap spacings of 1.5 and 0.7, the wake patterns change in the unsteady regime. For the gap spacing of 1.5, the wake pattern shows in-phase-synchronized, flip-flop and antiphase-synchronized patterns in turn according to vertical bar alpha vertical bar. For the gap spacing of 0.7, the flip-flopping wake pattern is changed as the in-phase-synchronized pattern behind the cylinder with the one-row vortex street in downstream with increasing vertical bar alpha vertical bar.