Mixing Flows

Turbulence is an excellent mixer. Here two fluorescent dyes are injected into a turbulent water jet. Flow is from the bottom of the image toward the top. The dyes are quickly mixed into the background fluid by momentum convection, their concentration decreasing with increased distance from the source. Large-scale structures like the eddies visible in this image drive this convection of momentum in turbulent flows. In contrast, consider laminar flows, where momentum and molecular diffusion dominate how fluids move. In such laminar flows, it’s even possible to unmix two fluids, a feat that cannot be accomplished in the jet above. (Photo credit: M. Kree et al.; via @AIP_Publishing)

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