Multistability and symmetry breaking in the two-dimensional flow around a square cylinder

We use numerical methods to study two-dimensional how passing a square cyli nder at low Reynolds numbers, and observe period-1 and -3 vortices behind t he cylinder at the same Reynolds number Re. When Re increases from a small number to a critical value Re(c)approximate to 320, the system could change from bistability, which maintains the spatial symmetry, to tristability, w hich breaks the spatial symmetry. Our results suggest many interesting prob lems for further studies. [S1063-651X(99)13711-5].