Disorder Suppresses Chaotic Viscoelastic Flow

Viscoelastic fluids transition from a steady to a chaotic and time-dependent flow beyond critical flow conditions, but little is known about the implications of geometric order/disorder for this transition. Utilizing microfluidics, we flow a purely elastic fluid through a hexagonal array of cylindrical pillars at a range of flow speeds, where the transition to chaotic flow occurs at a critical ratio of the polymer relaxation time to flow time scale (Deborah number), De ~ 1/2. The introduction of finite disorder to the system – corresponding to a random perturbation of the pillars by 10% of the lattice spacing – delays the transition to Deborah number, De ~ 1, and reduces the magnitude of the chaotic velocity fluctuations. Larger disorders appear to completely suppress the transition within the tested flow range up to De ~ 5. Examination of the Lagrangian strain rate correlations reveal that disorder broadens the distribution of excitation frequencies in the system, suggesting a potential mechanism for stabilizing the elastic flow.