Experimental Evidence of Helical Flow in Porous Media

Helical flow leads to deformation of solute plumes and enhances transverse mixing in porous media. We present experiments in which macroscopic helical flow is created by arranging different materials to obtain an anisotropic macroscopic permeability tensor with spatially variable orientation. The resulting helical flow entails twisting streamlines which cause a significant increase in lateral mass exchange and thus a large enhancement of plume dilution (up to 235%) compared to transport in homogenous media. The setup may be used to effectively mix solutes in parallel streams similarly to static mixers, but in porous media.

Figure 1

Photograph of the experimental setup: Top view of the two layers with alternate stripes of fine and coarse material used to build the heterogeneous anisotropic porous medium, and side views of the inlet and the outlet with marked injection and extraction ports, respectively.

Figure 2

Results of normalized concentration distributions at the outlet of the heterogeneous anisotropic flow-through system for the three experiments performed using different tracer injection ports. (a)–(c) The experimental results. (d)–(f) The model results. (g)–(i) The comparison between observed and simulated normalized concentrations.

Figure 3

(a)–(c) Streamlines traced from the inlet injection ports show a helical behavior; black lines: streamlines; colored surfaces: isosurfaces representing points with constant hydraulic head $\varphi$; grey surfaces: water level. (d)–(f) Flux-related dilution index observed (circles) and simulated (lines) at cross-sections along the travel distance in the three flow-through experiments.