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) (λ^bx/λ^by) 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). Copyright 2009 by the American Geophysical Union.