Abstract: The paper numerically investigates flow structures of single, two and multiple cylinders arranged in a shallow water flow. The shallow wakes are simulated with different shallow wake parameters and cylinder center-to-center spacings to investigate the effect of bottom friction and geometry on wake structures. The results show that with the increase of parameter, wakes tend to steady due to the increasing bottom friction, and large-scale vortex structures disappear gradually. Wakes behind multiply cylinders are influenced not only by parameter but also by spacing with the increase of spacing. Vortex street wake, unsteady vortex wake and steady vortex wake appear behind the single cylinder, sequentially. The single blunt body wake, biased and symmetry wakes occur behind two cylinders, and the single blunt body circumfence, biased wake, symmetry and asymmetry wakes appear behind three cylinders, sequentially. Besides, simulated results indicate that wake structures of multiply cylinders are different from that of single cylinder. The arrangement of multiply cylinders makes wakes more unsteady.

Key words: shallow water wake ,  , wake mode  , flow around circular cylinder  , bottom friction ,  , cylinder center-to-center spacing