It will be great if I could get some clarification on the calculation of the diffusive and dispersive mass flux in OGS5. Digging into the source code (rf_pcs.cpp, lines 11365-11511), I gather that:
- Effective diffusion coefficient (set up as model ‘1’ implying constant diffusion coefficient in .mcp input file) is calculated as:
<<Coefficient as defined in the .mcp input file>> * <<Tortuosity as defined in the .mmp input file>>*<<porosity as defined in the .mmp input file>>
- Dispersivity is calculated using darcy elemental velocity as:
<<Longitudinal alpha as defined in the .mmp input file>>*<>^2 + …similar in transverse direction …
- Dispersive mass flux along all relevant axes is then calculated accounting for porosity and concentration gradients along respective axes.
- Advective mass flux is also calculated using darcy elemental velocity
Please do share if the calculation above is not correct.
Lastly, the keywords page for diffusion coefficient says that the units of the constant diffusion coefficient are m2s-1. Is this also true if the Time unit in the .tim input file is specified as “DAY”?