Continuity error cannot be removed by adjusting the outflow

Now I am using preCICE for simulation two ways coupling Fluid Fluid coupling. At the interface, the velocity and gradient Velocity using to coupling but When I run having the error which I can not resolve.

Continuity error cannot be removed by adjusting the outflow.
Please check the velocity boundary conditions and/or run potentialFoam to initialise the outflow.
Total flux              : 105.971
Specified mass inflow   : 546831
Specified mass outflow  : 0
Adjustable mass outflow : 0

Do you know how to fix it!
Thank you for all advice.

@Hoaithanhbk_281113 this is too little information to understand what is going on. Could you please describe in more detail your setup? In particular, the boundary conditions on each participant, as well as what you are coupling, would be useful.

Note that fluid-fluid coupling is complicated, and it is for us also a field of active research at the moment.

Thank you for your reply!
this is the my simulation which was shown below picture.

I don’t know where the error you are getting could be coming from, but regarding the setup: shouldn’t you also be exchanging pressure or pressure gradient?

Generally, a tricky situation in your coupling is that you are coupling on the interface between two faces. So, I don’t think this is so easy. You would somehow need to map the physical properties of the one phase to the other.

It looks to me like you are trying to do a multiphase coupling instead of a multi-physics/multi-scale/multi-model coupling. I am afraid this needs quite some research and you will not be able to just configure a coupled simulation with the current code.

Thank you for your reply!

If I just want to simulate with one-way coupling does it mean that the gradient velocity of the water channel will be received from the air channel is this possible? I tried with one-way coupling but it seems to run independently of each other. Can you give me some suggestions if I solve it with one-way coupling?

Independent of one-way or bi-directional coupling, you need to take care of adapting your exchanged quantities according to the physical properties of each domain.

This sounds (almost) correct: The air channel sends the velocity gradient to the water channel, without waiting for the water channel to receive it before continuing.