Discussion Forum

I am trying to mimic the displacement of a fluid in a pipe by another fluid. I say mimic, rather than model, because characterizing the interface is irrelevant to the larger goal of my project. So my model is set up thusly: two adjacent domains (one for each fluid), with a boundary between them. Using the deformed geometry module, this boundary moves with time, expanding one domain and shrinking the other. This mimics the interface between the fluids. A simpler description of the model is that I am trying to solve for the velocity and pressure fields in a domain which is expanding with time.

Running a simulation without the deformed geometry finishes perfectly, and running just the deformed geometry works as well. But when combining them, the solver crashes. This is probably due to the moving boundary causing a violation of mass conservation. Does anyone have any suggestions about how to resolve this issue?