Influence of aperture field heterogeneity and anisotropy on dispersion regimes and dispersivity in single fractures

A 33 factorial experimental design was implemented to numerically investigate the interactive effect of the mean (μb), standard deviation (σb), and anisotropic ratio (AR) (λbx/λby) of single‐fracture apertures on dispersion regimes (specifically Taylor dispersion and geometric dispersion) and dispersivity. The Reynolds equation was solved to obtain the flow fields in each computer‐generated fracture, and the random walk particle tracking method was used to simulate solute transport. The simulation results show that (1) for a fixed hydraulic gradient, the dominant dispersion regime is controlled by μb, and to a lesser degree, σb, and geometric dispersion becomes more dominant as the coefficient of variation (COV) (σb/μb) increases; (2) for a fixed mean aperture, the dispersivity and the spread in dispersivity for varying ARs increases with the COV; and (3) the AR has a significant effect on dispersivity only when the COV is large (≳0.2).