  Viscoelastic flows through microscale porous arrays exhibit complex
path-selection and switching phenomena. However, understanding this process is
limited by a lack of studies linking between a single object and large arrays.
Here, we report experiments on viscoelastic flow past side-by-side
microcylinders with variable intercylinder gap. With increasing flow rate, a
sequence of two imperfect symmetry-breaking bifurcations forces selection of
either one or two of the three possible flow paths around the cylinders. Tuning
the gap length through the value where the first bifurcation becomes perfect
reveals regions of bi and tristability in a dimensionless flow rate-gap length
`phase' diagram.
