Separating stretching from folding in fluid mixing

Separating stretching from folding in fluid mixing

Fluid mixing controls many natural and industrial processes, including the spread of air pollution1, mass transfer and reactions in microfluidic devices2,3 and the detection of odours or other chemical signals4. Strongly nonlinear flows enhance mixing by chaotic advection5,6, stretching and folding7,8 fluid volumes. Though these processes have been studied in simple models9,10, stretching and f...

Experimental measurements of stretching fields in fluid mixing.

Using precision measurements of tracer particle trajectories in a two-dimensional fluid flow producing chaotic mixing, we directly measure the time-dependent stretching field. This quantity, previously available only numerically, attains local maxima along lines that coincide with the stable and unstable manifolds of hyperbolic fixed points of Poincaré maps. Contours of a passive impurity field...

Fluid mixing from viscous fingering.

Mixing efficiency at low Reynolds numbers can be enhanced by exploiting hydrodynamic instabilities that induce heterogeneity and disorder in the flow. The unstable displacement of fluids with different viscosities, or viscous fingering, provides a powerful mechanism to increase fluid-fluid interfacial area and enhance mixing. Here we describe the dissipative structure of miscible viscous finger...

Stretching Folding Instablility and Nanoemulsion

Stretching and folding in finite time.

Complex flows mix efficiently, and this process can be understood by considering the stretching and folding of material volumes. Although many metrics have been devised to characterize stretching, fewer are able to capture folding in a quantitative way in spatiotemporally variable flows. Here, we extend our previous methods based on the finite-time curving of fluid-element trajectories to nonze...