Problem in evaluating flow rate from stokes flow simulation

[BrinthanK]

We have a positive pressure gradient from inlet to outlet across a pore networks. Therefore, we expect the fluid to flow in but we get a value of Q>0, which according to OpenPNM means that the fluid is flowing out. Is there any reason as to why this is the case?

For context we are evaluating the permeability coefficient using the Darcy's law for which the flow rate is required. We are attaching the code snippit and the outcome of the code.

Thank you in advance.

[jgostick]

You have a lot of extra negatives signs in your code snippet above. I think they look right, but possibly they are the problem. The other problem might be where you are computing the rate. If you use the inlet pores the rate should be positive, but if you use the outlet pore it will be negative (with a magnitude equal to the inlet).

[BrinthanK]

Hey Jeff, thank you for your response. I have an additional question on top of this, that is, for the stokes law calculation what boundary values (i.e., flow.set_value_BC) should be, is it pressure or velocity?

Thank you.

[jgostick]

It just occurred to me that your problem might be caused by negative conductances. This can happen if your pores are too large and they overlap each other, resulting in a throat length that is negative. You should check this with something like np.sum(sf['throat.hydraulic_conductance'] < 0]). If it's not zero, then that is a problem...hopefully your only problem.

[spaul98]

For some reason, I get a 'key error' when I try to run the above line of code; (image attached)

[spaul98]

I am trying to simulate with a rate BC and P_out BC, to evaluate delP, as I mentioned before. Can you please confirm if the code below is atleast logically correct?

[spaul98]

Hi,
I just wanted to let you know that I think the top equation on this link: https://openpnm.org/examples/applications/effective_diffusivity_and_tortuosity.html is not represented correctly. You have D_ab on the left hand side of the equation but I think it should be on the right hand side and D_eff should be on the left hand side. Further down you have it correct. The description is also alright.
Thank you.

[jgostick]

good catch, thanks! I already fixed it. Nice to have such an easy fix.