In reality we'd alter the speed or resistance of the media. Then calculate the nondimensional numbers. We may also calculate the number and then alter the experimental whatever to give a nice plot.

In CFD we set stuff (speed, resistance coefficients etc) and can then find everything else. Depending on what is set we can also calculate the nondimensional numbers. But.... You are using a porous media approximation, so you use the permeability & other data to get the resistance coefficients in Fluent: they're based on resistance to flow. I can't say if you can directly equate the numbers as there are two components, C2 and 1/alpha which then use v^2 and v to determine pressure loss.

The issue with the above is I can do the pressure v flow experiment for a packed bed of spheres and a sponge and get the same resistance coefficients (if the two media are suitable). But, does that return the same Darcy Number? That I can't say as I don't know: as an industrial user of the code I'm interested in pressure loss, flow rate, heat flux etc and try to avoid the nondimensional comparisons.