  Viscoelastic flows transition from steady to time-dependent, chaotic dynamics
under critical flow conditions, but the implications of geometric disorder for
flow stability in these systems are unknown. Utilizing microfluidics, we flow a
viscoelastic fluid through arrays of cylindrical pillars, which are perturbed
from a hexagonal lattice with various degrees of geometric disorder. Small
disorder, corresponding to ~ 10% of the lattice constant, delays the transition
to higher flow speeds, while larger disorders exhibit near-complete suppression
of chaotic velocity fluctuations. We show that the mechanism facilitating flow
stability at high disorder is rooted in a shift from extension-dominated to
shear-dominated flow type with increasing disorder.
