Multiple states of turbulence at vanishing inertia

Abstract

Based on everyday experience fluid flows tend to be ordered and quiescent if inertial forces are low and held in check by viscosity. This intuition spectacularly fails in the case of complex macromolecular fluids like polymer melts, paints and biofluids. In such cases elastic fluid properties can drive turbulent motions at moderate and even vanishing Reynolds numbers. By studying viscoelastic flows in curved pipes we demonstrate that this low inertia phenomenology results from the competition of two hydrodynamic instabilities and respectively from the co-existence and interdependence of two distinct turbulent states. Unexpectedly the established categories of elastic and elasto-inertial turbulence (ET and EIT) fail to demarcate the actual turbulent states, fundamentally changing the perception of this phenomenon a century after its discovery.