At low Reynolds numbers, flow is laminar. No turbulence. Mixing happens only by diffusion, which is slow. This is the fundamental problem of microfluidics: you can move fluids through tiny channels, but you can’t stir them.

Unless the fluid is viscoelastic. DNA solutions, polymer melts, and biological fluids have elastic memory — they store energy during deformation and release it later. At low Reynolds numbers where inertial turbulence is impossible, these fluids generate elastic turbulence: chaotic flow driven by the polymer’s own stress, not by inertia.

The mechanism is wave-based. Viscoelastic waves — oscillations in the polymer stress field — propagate through the fluid and interact nonlinearly, generating the irregular flow patterns that mix the fluid. The waves don’t need inertia. They need elasticity. The fluid’s memory of its own deformation creates the disorder that drives mixing.

The practical result: rapid chemical synthesis in microchannels using DNA or polymer additives. The same property that makes biological fluids difficult to model (their non-Newtonian behavior) is the property that makes them useful as mixing agents. The complexity is the feature.

The deeper lesson: turbulence is not one phenomenon. Inertial turbulence and elastic turbulence look similar — both produce chaotic, mixing flow — but they arise from completely different physics. Reynolds number tells you about one. The Weissenberg number tells you about the other. A fluid can be turbulent at any Reynolds number if its elasticity is high enough.