This paper aims to simulate unstable gap flows of three side-by-side cylinders unequally/equally spaced at T1/d = 1.5 and T2/d = 1.6 in a uniform cross flow (Re=300). The simulation is carried out using ANSYS Flotran 7.0. A mesh-independent study is conducted on a single cylinder at Re=100. The Strouhal number and wake flow characteristics compare well with experimental results. Simulation of three side-by-side cylinders in uniform cross flow has revealed that the gap flows are unstable and constantly re-orientating, which has the effect of restructuring the wake flows behind the cylinders. The flow field for unequal spacing of the cylinders is similar to the equal spacing case for some period of time with a symmetrical near wake. However, at other times, the wake flow is asymmetrical. This agrees well with the visualisation of Wang et al. (2002), in which the gap flows and the wake flow are constantly in transition
