Irreversible dispersion at a stagnation point: Experiments and lattice Boltzmann simulations

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Abstract
Tracers convected through porous media disperse irreversibly. We studied the reversibility of a tracer line across a channel, dispersing in creeping (low Reynolds number) high Péclet number flow around a cylinder. Flow reversal at a time t returned the line to start at 2t. At the midchannel position of this ‘‘echo,’’ we measured an effective dispersion exceeding molecular diffusion by 2 orders of magnitude. A new lattice Boltzmann model adapted to the experiments described them accurately. This first test of lattice Boltzmann simulations on dispersion experiments yields excellent agreement.